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• BaSnS 3 and AgTaS 3 absorbers based tandem solar cell has been designed. • Top cell has the structure of n-WS 2 / p -BaSnS 3 / p +-MoS 2 heterojunction. • Bottom cell has been configured as n -WS 2 / p -AgTaS 3 / p +-GeS heterojunction. • Cell shows an efficiency of 42.57 % with a V OC = 2.03 V, J SC = 23.29 mA/cm2, FF = 89.85 % • The findings reveal the viability of all-inorganic perovskite-based tandem solar cells. Perovskite materials are revolutionizing the solar cell (SC) industry, continually enhancing their properties and establishing a prominent photovoltaic technology. Among these, BaSnS 3 (BTS) and AgTaS 3 (ATS) stand out for their strong potential as absorber layers. These inorganic chalcogenide perovskites address the drawbacks of their organic counterparts, being both lead-free and non-toxic, thereby making them highly suitable for photovoltaic (PV) applications. The exploration of BTS and ATS as absorber layers in a tandem solar cell's top and bottom cells has yielded remarkable outcomes. The innovative tandem solar cell design features a top cell structured as n-WS 2 / p -BaSnS 3 / p +-MoS 2 and a bottom cell configured as n -WS 2 / p -AgTaS 3 / p +-GeS. This theoretical study using SCAPS-1D demonstrates a high efficiency of 42.57 % with a V OC of 2.03 V, a J SC of 23.29 mA/cm2, and an FF of 89.85 %. These impressive results are achieved with adjusted layer thickness, carrier doping and defect levels, highlighting the strong potential of BaSnS 3 and AgTaS 3 photoactive materials. The findings reveal the viability of innovative, all-inorganic perovskite-based tandem solar cells, offering a promising avenue for future sustainable and high-efficiency photovoltaic device technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • n-TOPCon Type-1 bottom cell achieved the highest efficiency of 6.33%. • Integrated III–V Flex Cell with n-TOPCon1 reached 35.4% efficiency. • EQE and Jsc analyses highlighted optimal spectral response. • Series and shunt resistances key to electrical behavior under dark conditions. • Tandem solar cells exceed single-junction efficiency limits. This study explores the advancement of high-efficiency tandem solar cells by integrating crystalline silicon (c-Si) technologies—specifically n-TOPCon, p-PERC, and n-HJT—with III–V semiconductor materials. Through detailed analysis of current–voltage (IV) characteristics, external quantum efficiency (EQE), and dark current-voltages (DIV) behavior, this study aims to optimize these cells for tandem applications. The n-TOPCon Type-1 bottom cell demonstrated the highest efficiency (η) of 6.33 %, with a short-circuit current density (J sc) of 12.91 mA/cm2, an open-circuit voltage (V oc) of 0.679 V, and a fill factor (FF) of 72.12 % by matching the current with top III–V multijunction cell. The n-TOPCon Type-2 and p-PERC cells showed competitive performance, achieving η of 5.63 % and 5.44 % respectively. The n-HJT cell, despite its highest V oc of 0.681 V, had a slightly lower η of 5.33 %. When integrated with III–V cells, these configurations achieved substantial efficiency gains. Notably in tandem configurations, the n-TOPCon-1 with III–V 3J (three-junction) Flex Cell in series achieved an η of 35.4 %, with a J sc of 12.91 mA/cm2, V oc of 3.663 V, and FF of 77.56 %. The EQE and integrated J sc analyses highlighted the spectral response and efficiency of the triple-junction flexible solar cell, while the DIV characteristics provided insights into electrical behavior under dark conditions. Overall, this study underscores the potential of c-Si and III–V tandem solar cells to exceed single-junction efficiency limits, highlighting the importance of innovation and optimization in photovoltaic technology for achieving more efficient and reliable solar energy solutions. [ABSTRACT FROM AUTHOR]

• Optical performance of InP TNP/Ge Tandem Solar Cell (SC) studied using FDTD method. • Geometrical optimisation of individual subcells performed to achieve current matching. • Doping concentration of each cell is optimised to achieve high efficiency. • Analytical modelling is performed to obtain the photovoltaic parameters of Tandem SC. • PCE of 26.7% is achieved for InP TNP/Ge multijunction SC. The rapid progress in photovoltaic sector is motivating researchers to carry out exhaustive investigation of highly efficient, cost-effective solar cells by lowering active material requirements or employing nanostructured Solar Cells (SCs). The detailed-balancing Shockley-Queisser limit of efficiency for thin-film or nanostructure single-junction p–n junction SC imposes a restriction on the Power Conversion Efficiency (PCE) corresponding to a particular material. However, by stacking multiple layers of variable bandgap energy materials, the efficiency of the SC can be enhanced to exceed the Shockley-Queisser limit in a multijunction (tandem) SC. In this article, we have stacked two semiconducting layers of different bandgap energies in series in the form of InP truncated nanopyramid (TNP) as a top subcell (E g = 1.35 eV) grown over Ge substrate as a bottom subcell (E g = 0.78 eV) and explored the optoelectronic study of this InP TNP on Ge multijunction (tandem) SC using the Ansys Lumerical software. The height of InP TNP nanostructure and thickness of Ge substrate are optimized to achieve equal current density (J sc) in order to fulfill the current matching condition for a tandem SC. J sc of 23.1 mA/cm2 and 22.9 mA/cm2 are obtained for InP TNP with height h 1 = 1 μm and Ge substrate with height h 2 = 700 nm, respectively. For the electrical analysis of the InP TNP and Ge subcells, we have optimized the doping profile of the p-n region of each subcell in order to obtain a similar electrical J sc. Finally, we have obtained the J-V plot of the proposed tandem SC using the mathematical equations for two series connected photovoltaic cells. [ABSTRACT FROM AUTHOR]

Until present, high-performance perovskite solar cells (PSCs) are normally fabricated on the transparent conductive glass as both the substrate and light-incident side, referred to as bottom-incident PSCs (BIPSCs) in this work, while inferior cost, limited transmittance, and poor conductivity restrict their market competitiveness in photovoltaic communities. Recently, an alternative type of PSC with top-incident characteristics (TIPSC) attracted great interest owing to the advantages of the flexibility of substrates, the compatibility with tandem design, and the versatility of applications; but their studies are still in infancy. Here, advanced research progresses on TIPSCs following the configuration logic of devices are systematically summarized. Specific parameters and key demands are extracted to assess the performance of TIPSCs, as well as to propose the ideal device structure and material collocation through comprehensive discussions. Prospects for the development of high-performance TIPSCs are also presented, which hopefully catch up with the mainstream BIPSCs and guide the upcoming research hotspots. [Display omitted] • Top-incident (TI) perovskite solar cells (PSCs) could be fabricated on arbitrary substrate materials. • TIPSCs exhibit superior cost, high tandem compatibility, and diverse application scenarios than BIPSCs. • TIPSC has been reviewed as a new category of perovskite-based photovoltaics. • Four critical components in TIPSCs with corresponding major challenges and improvement strategies were discussed. • Five promising future research directions of TIPSC were highlighted. [ABSTRACT FROM AUTHOR]

• Sputtered MoS 2 :Nb films are investigated as infrared-transparent contacts. • The influence of sputtering pressure on the MoS 2 :Nb films properties is discussed. • Despite Nb-doping, a n-type conductivity is found and discussed. • The high work function (≈5 eV) makes the films suitable as hole transport layer. • MoS2 films are tested in single Cu2ZnSnS4 and tandem Cu2ZnSnS4/c-Si solar cells. MoS 2 :Nb films deposited by radio-frequency magnetron sputtering are investigated in view of their application in infrared (IR)-transparent contacts for tandem photovoltaic devices. This material is already known to give a good electrical contact with p-type chalcogenide semiconductors, which are typically grown onto opaque molybdenum metallic contacts and a MoS 2 layer spontaneously forms at the back interface during the on-top semiconductor growth. Our study explores a different approach, which involves the direct growth of IR-transparent MoS 2 :Nb films via sputtering inside complete photovoltaic devices, like Cu 2 ZnSnS 4 (CZTS)-based single junction solar cells and CZTS/Si tandem devices. Films deposited at different sputtering pressures are compared by analysing their microstructure, morphology, chemical composition, optical and electrical properties. The effects of post-deposition sulfurization treatments are also investigated. We find that MoS 2 :Nb films deposited at around 0.1 Pa exhibit compactness but show a notable sulfur deficit ([S]/[Mo]≈1.4), a significant sub-bandgap optical absorptance and lack of crystallinity. Increasing the Ar pressure to 1 Pa raises the [S]/[Mo] ratio to 2.2, yielding crystalline films with good IR-transparency, although with a porous morphology. Despite 0.5 wt% Nb-doping of the sputtering target, the as-deposited films demonstrate n-type conductivity likely due to uncontrolled impurities and intrinsic defects. Ultraviolet Photoemission Spectroscopy measurements suggest that films' work function higher than 5 eV can be obtained with a post-deposition sulfurization, making these materials suitable as Hole Transport Layer in photovoltaic applications. A similar increase in work function is expected in the CZTS/MoS 2 junctions, since the sputtered MoS 2 :Nb films undergo a sulfurization process needed to obtain the overlying polycrystalline CZTS absorber. CZTS solar cells produced with sputtered MoS 2 and Transparent Conductive Oxides contacts on glass substrates, despite plagued by severe adhesion problems, show the potentiality to give efficiencies comparable to reference devices with standard Mo back contact. Fabrication of CZTS/Si tandem devices on textured silicon bottom cells yields a maximum efficiency of 4.4 %, primarily hindered by the low quality of the CZTS film on textured substrates. Nonetheless, optoelectronic characterizations based on both spectrophotometric and quantum efficiency measurements confirm a good IR transparency of the MoS 2 -based intermediate contacts and the desired electrical behaviour. [ABSTRACT FROM AUTHOR]

To avoid Shockley-Queisser limit in single p-n junctions, tandem solar cells were proposed. A new tandem cell is simulated here using the 1-dimensional SCAPS. The new cell combines two reported single solar cells together, aiming at achieving high performance by optimizing various layer characteristics. The bottom sub-cell is Mo/Si(p)/CZTSSe(p)/CdS(n)/ZnO(i)/ZnO(Al), where ZnO is an electrodeposited transparent-conductor oxide, with high UV transmittance, ZnO(i) is intrinsic layer, CZTSSe/Si is bi-absorber layer of p-CuZnSnSSe and p-Si, Mo is back contact. The optimized sub-cell exhibits a high fill factor of 85.18 % with overall efficiency 20 %. Based on literature, a perovskite CsPbI 2 Br layer is included in the top sub-cell Cu 2 O(HTL)/CsPbI 2 Br)/TiO 2 (ETL), where Cu 2 O is a hole-transport layer and TiO 2 is electron-transport layer. The top sub-cell layers have been carefully selected for best alignment. Matching and optimizing various parameters in the two sub-cells is a simulation challenge. Therefore, layers in the two sub-cells have been studied separately, keeping in mind the proper combinations between various layers. With optimized layer thicknesses and band gaps, together with proper alignment of band edges, the proposed tandem solar cell exhibits high characteristics of 80 % fill factor and higher than 32 % overall efficiency. [Display omitted] • A new tandem-solar cell with CZTSSe/Si and CsPbI 2 Br perovskite in bottom and top sub-cells, respectively, is proposed. • ZnO(Al) is used as a TCO. Its experimental and literature properties are used in the simulations. • The bottom sub-cell is optimized by simulating (using Scaps) layer thicknesses, doping concentrations and band gaps. • The optimized cell is simulated using optimal bottom sub-cell parameters, and matched with top sub-cell parameters. • A high conversion efficiency of more than 32% is observed for the optimized tandem cell. [ABSTRACT FROM AUTHOR]

• Low-cost industrial silicon heterojunction solar cells were used for bottom cells. • Large-area perovskite surface passivation process was conducted based on a scalable slot-die coating method. • The small size TSC device (2.5 × 2.5 cm2, aperture area of 1 × 1 cm2) fabricated by slot-die coating exhibited efficiency of 28.68 %. • A champion efficiency of 24.22 % and open-circuit voltage of 1.915 V was obtained in 5 × 5 cm2 TSC device (aperture area of 3.8 × 3.8 cm2). Tandem solar cells composed of perovskite and silicon (PVSK/Si TSCs) exhibit significant potential for improving the power conversion efficiency (PCE) and reducing the levelized cost of electricity. Currently, most tandem cells demonstrating high efficiencies utilize costly float zone (FZ) silicon wafers, which pose limitations for large-scale production due to their high expense. This study presents a scalable approach for manufacturing perovskite/silicon tandem solar cells using industrial silicon bottom cells. We employ a double-layer intrinsic amorphous silicon passivation layer to enhance the carrier lifetime of the bottom silicon cell. Additionally, we introduce a novel indium oxide doped with transition metals (IMO) transparent electrode to enhance near-infrared (NIR) light absorption. To achieve silicon bottom cells with a polished front surface, we utilize a cost-effective and time-saving saw damage etching process. The perovskite absorber is then deposited on the polished surface using slot-die coating. Furthermore, we coat the perovskite absorber with a mixed solution of FAI and mF-PEAI via slot-die coating to eliminate excess PbI 2 on the surface and passivate surface defects. Through the integration of top and bottom sub-cells, we obtained a PCE exceeding 24.22 % from a 5 cm × 5 cm TSCs device (with an aperture area of 3.8 cm × 3.8 cm) and a PCE of 28.68 % from a 2.5 cm × 2.5 cm TSCs device (with an aperture area of 1 cm × 1 cm). [ABSTRACT FROM AUTHOR]

Detailed balance limit of perovskite/Si tandem solar cells with two-terminal (2T), four-terminal (4T), and series parallel tandem (SPT) configurations was calculated under a constant bandgap (E g-bottom) of 1.12 eV of Si bottom subcells. Performances in the 2T configuration are most influenced by the E g-top , because E g-top can result in current mismatching if E g-top is not appropriate. The ideal E g-top values are 1.73 eV for 2T, 1.82 eV for 4T, and 1.83 eV for SPT under standard AM1.5G spectrum. Consequently, with the ideal E g-top values, the highest possible efficiency (η) values are 44.8% for 2T, 45.0% for 4T and 44.7% for SPT. Furthermore, detailed balance limit under actual outdoor environmental factors at Shiga-prefecture in Japan was scrutinized. It is found that the outdoor spectral variation has the significant impact on the efficiency limit especially in a case of 2T. Also, the outdoor solar spectra at this observed outdoor location mostly are the blue-rich spectra over a year. As a result, the perovskite/Si tandem solar cell with the large ideal E g-top of 1.82 eV in 4T configuration is the most appropriate to generate the possible highest η, thereby resulting in the highest annual energy generation. [ABSTRACT FROM AUTHOR]

• Effects of interface defect density and band offset on properties of CsPbIBr 2 PSCs are investigated. • PCE of 15.05% with a V OC of 1.54 V is obtained for the with FTO/ZnOS/CsPbIBr 2 /CuAlO 2 /Au PSCs. • Two-terminal all-perovskite TSCs are constructed, and a maximum PCE of 27.4% is obtained. • Four-terminal triple-junction TSCs are constructed, and a maximum PCE of 35.35% is achieved. More and more attention has been paid to CsPbIBr 2 material for perovskite solar cells (PSCs), owing to the trade-off between bandgap and stability. However, the reported maximum power conversion efficiency (PCE) of CsPbIBr 2 PSCs is lag behind that of the congeners due to the serious interface recombination of charge carriers. In this work, the effects of interface defect density and interface band offset on the properties of CsPbIBr 2 PSCs are investigated. It is found that the characteristic of the front electron transfer layer (ETL)/perovskite interface has a significant influence on the performance of PSCs than that of the back perovskite/hole transfer layer (HTL) interface. Additionally, a PCE of 15.05% with a high open-circuit voltage (V OC) of 1.54 V is obtained for the PSCs with FTO/ZnOS/CsPbIBr 2 /CuAlO 2 /Au structure. Finally, two-terminal monolithic all-perovskite double-junction tandem solar cells (TSCs) with the architecture of FTO/ZnOS/CsPbIBr 2 /CuAlO 2 /ITO/TiO 2 /MAPbI 3 /Spiro-MeOTAD/Au are constructed, and a maximum PCE of 27.4% (V OC of 2.60 V, J SC of 12.21 mA/cm2, and FF of 86.42%) is obtained for the TSCs with top and bottom absorber thicknesses of 600 nm and 500 nm respectively. Furthermore, four-terminal triple-junction TSCs are designed with silicon solar cells as bottom sub-cell, and a maximum PCE of 35.35% is achieved. These results will provide theoretical guidance for the fabrication of high performance TSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] The power conversion efficiency for single-junction solar cells is limited by the Shockley-Quiesser limit. An effective approach to realize high efficiency is to develop multi-junction cells. These years have witnessed the rapid development of organic–inorganic perovskite solar cells. The excellent optoelectronic properties and tunable bandgaps of perovskite materials make them potential candidates for developing tandem solar cells, by combining with silicon, Cu(In,Ga)Se 2 and organic solar cells. In this review, we present the recent progress of perovskite-based tandem solar cells, including perovskite/silicon, perovskite/perovskite, perovskite/Cu(In,Ga)Se 2 , and perovskite/organic cells. Finally, the challenges and opportunities for perovskite-based tandem solar cells are discussed. [ABSTRACT FROM AUTHOR]

• The working mechanism of 2-T and 4-T CsPb(I 1−x Br x) 3 /c-Si TSCs are investigated. • The influence of Eg and thickness of the top sub-cell on the properties of TSCs is studied. • A maximum PCE of 29.23% is achieved for the 2-T TSCs with CsPbI 3 as top sub-cell. • PCEs above 28.5% can be obtained for the 4-T TSCS with CsPbBr 3 as top sub-cell. • 4-T TSCs possesses a more wider design window than its 2-T counterpart. It is well known that the phase stability of CsPb(I 1−x Br x) 3 (0 ≤ x ≤ 1) perovskite materials is enhanced under humid environments with the increase of Br− concentration in film, however, the bandgap (E g) is also widened synchronously, resulted in limiting the light harvesting and then reducing the power conversion efficiency (PCE) of devices. Hence, how to realize the compatibility of high stability and high PCE is a challenge for device based on CsPb(I 1−x Br x) 3. In this work, the two- (2-T) and four-terminal (4-T) tandem solar cells (TSCs) consisting of a CsPb(I 1−x Br x) 3 top sub-cell and a crystalline silicon (c-Si) bottom sub-cell are constructed and compared. It is found that in the case of 2-T configuration, performance of device is very sensitive to the E g and the thickness of top sub-cell, and a maximum PCE of 29.23% is achieved only for the CsPbI 3 top sub-cell at an optimum thickness of 275 nm. However, in the 4-T formation, devices present a weak dependence on the E g and the thickness of top sub-cell, and PCEs above 28.5% can be obtained when CsPbBr 3 is used as top sub-cell. These results highly underline the application potential of 4-T CsPb(I 1−x Br x) 3 /Si TSCs, especially for CsPbBr 3 /Si TSC. [ABSTRACT FROM AUTHOR]

• Continuous Ag films with percolation threshold of 5 nm were realized by Cu seed layer. • Semitransparent PSCs with 6 nm Ag electrodes exhibited PCE of 14.5%, maintaining 88% performance of opaque PSCs. • Average transmittance of PSCs in 800–1200 nm was improved to 58.6% by optical coupling layer. • Tandem solar cells using semitransparent PSCs and c-Si cells were demonstrated. Tandem solar cells with top perovskite solar cells (PSCs) have attracted great attention due to the rapid progress in power conversion efficiency (PCE). Ultrathin silver (Ag) metals with low percolation threshold are promising candidates as transparent electrodes for semitransparent PSCs. In this work, continuous Ag films with percolation threshold lower than 6 nm were realized through Cu seed layer, which guaranteed not only excellent conductivity but also broadband transparency. As a result, semitransparent PSCs with 6 nm Ag electrodes exhibited PCE of 14.5%, maintaining 88% performance of the opaque PSCs. Moreover, the average transmittance of semitransparent PSCs in the range of 800–1200 nm was improved to 58.6% using zinc oxide as optical coupling layer, promising near infrared light absorption by bottom solar cells. Ultimately, four-terminal tandem solar cell using semitransparent PSC and homogenous crystalline silicon solar cell was demonstrated. Furthermore, the strategies of using 5 nm Ag electrodes combined with Ag grids, and optical coupling layers with higher refractive index, were suggested to further increase the PCE of tandem solar cells. The proposed ultrathin Ag transparent electrodes are ease of fabrication as well as good optoelectrical properties, which are promising for application in semitransparent PSCs and tandem solar cells. [ABSTRACT FROM AUTHOR]

Lead-free Hybrid Organic-Inorganic perovskite have gained remarkable interest for photovoltaic application due to their lack of toxicity. In this work, We report the findings obtained from simulation with the SCAPS-1D software of an all Pb-free perovskite solar tandem device. The (CsGeI3) with 1.6 eV band gap is employed as a top-cell, while, the bottom-cell is FASnI3 with a band gap of 1.41 eV. Initially, individual sub-cell improvement was carried out through varying the solar cell's parameters, starting with the absorber thickness, the ETL and HTL electron affinities, and the capture cross-section. Then, The tandem solar cell is then constructed using these individually optimized sub-cells. A current matching J SC of 16.71 mA/cm2 was produced between the top and bottom sub-cell thickness of 220 nm and 1400 nm, respectively. The tandem device simulation with CsGeI3 on FASnI3 yielding a PCE of 30.42%, V oc = 2.12 V; J sc = 16.71 mA/cm2, and FF= 85.87%, that was much greater than each sub-cells output. The findings of this study demonstrate the possibility of using lead-free perovskite, such as FASnI3, to produce high PCE in tandem devices. [ABSTRACT FROM AUTHOR]

• Alternatively, promising ETL, such as SnO 2 , has recently emerged, producing remarkable performance in PSCs. • The outstanding performance in SnO 2 -based ETL is owing to its extraordinary properties. • The best reported result with η = 25.4 % for SnO 2 ETL has been achieved. • The SnO 2 -based PSCs exhibited η greater than 20 % and stability >1000 h. Perovskite solar cells (PSCs) have appeared as a growing photovoltaic technology owing to their unprecedented performance compared to the market leader, silicon solar cells. The high efficiency (η) of 26 % within a decade brings hope for the photovoltaic community. However, their operational stability remains a critical issue and hinders their commercialization. Charge transport layers play a key role in the stability and overall performance of PSCs. While TiO 2 is the most common and successfully employed electron transport layer (ETL), it is neither a very efficient charge extractor at the interfaces nor stable under UV illumination. Alternatively, another promising ETL, such as SnO 2 , has recently emerged, producing remarkable performance in PSCs. The outstanding performance in SnO 2 -based ETL is owing to its extraordinary properties, such as its better band alignment with common perovskite material and higher mobility while being processable at low temperatures (∼150 °C). The best reported result with η = 25.4 % for SnO 2 ETL has been achieved so far, comparable to that of the most employed ETL-based TiO 2 (η = 26 %). In this review, recent progresses in SnO 2 -based PSCs with η greater than 20 % and stability (>1000 h) are summarized together with a discussion on associated challenges and opportunities, with an emphasis on the road ahead for commercialization. [ABSTRACT FROM AUTHOR]

Tandem solar cell (TSC) architectures have gained tremendous attention due to wide range absorption and high efficiency. These architectures involve the combination of multiple nanomaterials that complement absorption characteristics of each other. In recent, emerging perovskite photoactive materials with their strong absorption coefficient of high-energy photons in the UV-Vis regions, are particularly well-suited for this purpose. Integration of perovskite solar cells (PSCs) and infrared (IR) absorbing solar cells in TSC significantly enhances the overall performance. This review critically examines the progress made particularly in perovskite-based TSCs, with a specific focus on the material structure, bandgap engineering, and crystallization techniques employed. Detailed descriptions and analyses are provided for the development of different types of TSCs, including perovskite/inorganic, perovskite/organic, perovskite/dye-sensitizer, perovskite/perovskite, and perovskite/quantum dots (QDs)-based solar cells. The challenges associated with perovskite-based TSCs are also highlighted, emphasizing the need for further investigation in specific areas. Overall, a comprehensive analysis presented in this review provides valuable insights into the advancements and future research directions for perovskite-based TSCs. [Display omitted] • Tandem Solar Cell (TSC) architectures promise broad spectrum absorption and high efficiency. • Integration of perovskite PVs with established technologies like Si or CIGS has been explored. • This review covers various Vis/IR-absorbing materials, providing valuable insights and future research directions for perovskite-based TSCs. [ABSTRACT FROM AUTHOR]

Given the increasing interest in tandem silicon-based solar cells and the recent advances in luminescent solar concentrators, the luminescent solar concentrators/silicon tandem structure has been proposed as an option for a four-terminal tandem structure. As part of the evaluation of a new type of solar cell, it is important to conduct a Life Cycle Assessment to effectively guide research efforts towards cell designs with minimum environmental impacts. Here, we carry out a process-based Life Cycle Assessment to assess global warming, human toxicity (carcinogenic and non-carcinogenic), freshwater eutrophication and ecotoxicity and abiotic depletion potential impacts associated with three luminescent solar concentrators/silicon tandem cell structures, considering a bottom layer as being a passivated emitter rear contact silicon solar cell. The results are based on experimental parameters and show that the increase in the performance of the cells and modules using the studied tandem structure can produce lower environmental effects than the passivated emitter rear contact technology (single-junction) for the impact categories studied. These results encourage the studies on cell and module performance improvements using such tandem luminescent solar concentrators/silicon structures. • The use of a LSC/Si tandem produces lower environmental impacts than Si (PERC) technology. • The disposal of the LSC/Si tandem PV modules to landfill has significant impacts. • The use of quantum dots (QD) leads to high toxicity potential. [ABSTRACT FROM AUTHOR]

• Drift-diffusion based optimization of all-perovskite two-terminal tandem solar cells. • Thickness, bandgap, and contact workfunction optimization is done to achieve maximum efficiency. • Investigation of effect of traps, mobility, and transport layer doping. • Efficiency of 36.6% for an ideal system and up to 29.8% for a 2T tandem cells with recombination losses is predicted. • Efficiency varies from 21% to 25.5% while varying cathode workfunction. Organic-inorganic (hybrid) perovskite semiconductors offer a wide range of bandgaps, low-cost deposition, and wide optical absorption, making them an ideal candidate for new photovoltaic devices. All-perovskite two terminal (2T) tandem solar cells have the potential to achieve high efficiency and at the same time offer cost-effective fabrication. In a 2T tandem cell, it is needed to optimize various device parameters such as bandgaps and thicknesses of the subcells, in order to make the best use of the available solar spectrum. In this study, we propose a drift-diffusion (DD) simulation model to optimize the bandgaps and thicknesses of the top and bottom cells in all-perovskite 2T tandem solar cell. Using our simulation model, we investigated the effect of interface and bulk traps, mobility, doping of the charge transport layers and contact workfunctions to the power conversion efficiency. We calculated up to 36.6% efficiency for an ideal device. We found that the traps at the interfaces and in the bulk perovskite films are the most important factor hampering the tandem cell efficiency. We predicted up to 29.8% efficiency for a device with recombination losses. By changing the mobility in the active material of the bottom cell we found that, the mobility plays an important role in determining the optimum thicknesses of the top and the bottom cells. Optimizing cathode workfunctions leads to a 3–4% improvement in the efficiency. Our study will help to understand the role of various factors limiting tandem cell efficiency and ways to optimize the device parameters to ensure the best performing all-perovskite 2T tandem solar cell. [ABSTRACT FROM AUTHOR]

Abstract Solar cells based on CuInSe 2 (CIS) with absorber bandgap 1.0 eV are excellent candidates for a bottom cell in a tandem solar cell. This work investigates the effect of alloys of Ag and small amounts of Ga as an approach to improve the efficiency of CIS-based solar cells with bandgap less than 1.1 eV. Ga and Ag influence the surface morphology of the absorber layer, and Ag alloyed solar cells also have an increased concentration of Ag relative to Cu at the surface. Despite these structural and compositional differences compared to CuInSe 2 , the device with the highest efficiency incorporates a mixture of Ga and Ag alloying to form (Ag,Cu)(In,Ga)Se 2 , where Ga addition improves the open circuit voltage and Ag addition improves the short circuit current. Ag improves current collection from long wavelength light due to the larger space charge width of Ag alloyed solar cells. However, Ag alloyed devices demonstrate lower V OC due to an interface recombination mechanism. Highlights • (Ag,Cu)(In,Ga)Se 2 has increased current collection at long wavelengths. • (Ag,Cu)(In,Ga)Se 2 has improved short-circuit current due to larger depletion width. • (Ag,Cu)(In,Ga)Se 2 is suitable for the bottom cell in tandem solar cells. • (Ag,Cu)(In,Ga)Se 2 is affected by an interface recombination mechanism. [ABSTRACT FROM AUTHOR]

For tandem solar cells (TSCs), the highest efficiency is generally believed to occur when the top and bottom sub-cells obtain an identical photocurrent, i.e. , the current-match condition. However, the real situation is that there is a slight deviation from the matching point, which is an interesting phenomenon, but lacks a clear explanation. Here, we report a coupled photoelectric investigation on the intrinsic mechanisms within TSCs under various current configurations. Taking an all-perovskite TSC as an example, we find that the efficiency deviation originates from the current reduction and fill factor (FF) compensation; moreover, the optimal efficiency depends primarily on the sub-cells with higher FF. Our analysis further reveals that the higher FF and efficiency are achieved under current-mismatch condition due to the differentiated voltage assignments among the sub-cells, i.e. , the sub-cells with higher currents require larger voltages in order to effectively recombine the surplus currents. We also find that the impact of sub-cell leakage on TSC performance can be partially alleviated by increasing the current of the affected sub-cell. Such an optoelectronic insight offers a valuable guidance for designing high-efficiency TSCs. [Display omitted] ● A comprehensive photoelectric coupled model of tandem photovoltaic operating under current-mismatch conditions was developed. ● Origin of FF compensation effect under current mismatch conditions was identified. ● Imposing current limits on sub-cells with superior performance can effectively enhance overall TSC performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A synergistic combination of MAI and DMSO resulted in ionic exchange with PEDOT:PSS. • Ionic exchange addressed the spatial separation issues of PEDOT- and PSS-rich domains. • Ionic exchanged PEDOT:PSS surface improves buried interface with Sn-Pb perovskite. • Feasibility of ionic exchanged PEDOT:PSS for 2 T all-perovskite tandem PV confirmed. To apply Sn-Pb mixed perovskite solar cells for highly efficient single- or multi-junction devices, understanding device-specific buried interfaces is necessary. Poly [3,4-ethylenedioxythiophene]:poly[styrene sulfonate] (PEDOT:PSS) is primarily used as a hole transport layer in Sn-Pb mixed perovskite solar cells. However, the spatial heterogeneity of PEDOT:PSS, caused by its PEDOT-rich and PSS-rich domains, induces many defects at the buried interface in PEDOT:PSS/perovskite, which limits device performance. Here, we present ionic exchange (IE) of PEDOT:PSS via a combination of methylamine iodide (MAI) and dimethyl sulfoxide (DMSO). Through surface analyses and density functional theory (DFT) simulations, we confirm that the IE process preferentially form PEDOT-I and MA-PSS and that PSS-rich domains bind to DMSO. Thus, the spatial separation of PEDOT:PSS is solved, and the exchanged MA+ and I− ions serve as a bridge between PEDOT:PSS and the perovskite, leading to improved physical, chemical, and electrical properties of the buried interface. The Sn-Pb mixed perovskite solar cells using IE-PEDOT:PSS achieve an improved efficiency of 21.3 % with an open-circuit voltage of 0.85 V and show better long-term stability. Additionally, IE-PEDOT:PSS works effectively in 2-terminal all-perovskite tandem devices, resulting in an improved efficiency of 23.5 % and high reproducibility. [ABSTRACT FROM AUTHOR]

Tandem Solar cells are composed of multiple layers with varying bandgap materials to facilitate the absorption of a wider range of solar energy. However, their performance is hampered by interface losses leading to current mismatching. To overcome these limitations, tandem solar cells often require the use of mirrors and lenses to concentrate and trap light to achieve optimal efficiency. Recently, the use of nanoscale 2D meta-materials has emerged as a promising alternative to traditional lenses. However, the optical optimization of these meta-materials can be both time-consuming, resources, and space-intensive, posing a challenge to their implementation. This study explores the use of deep learning to predict the optimal optical design for the top cell in tandem solar cells to maximize power conversion efficiency. Computational techniques are used to analyze the optical responses of metasurfaces. 2D-Convolutional Neural Networks (CNN) are used to train a dataset of 10,578 T i O 2 / C H 3 N H 3 P B r 3 / Z n O metasurfaces. Nine different CNN models were used with different architectures to identify the best hyperparameters that give the low mean square error. CNN displayed fast high prediction accuracy taking an average of 0.3 ± 0.05 seconds per prediction. The Deep SHapley Additive Explanations (SHAP) algorithm was used to gain insights into CNN's predictions and understand the behavior of complex metasurfaces integrated into a typical reference tandem solar cell architecture. The proposed metasurfaces can significantly enhance the efficiency of tandem solar cells. The active layer comprises of near 90% absorption of the solar spectrum. The average absorption of the top cell increased in the UV-vis region (650-800nm) up to 93.4%. • We trained 2D-CNN to predict the optimal metasurface for tandem solar cells. • CNN predictions were generated much faster, taking an average of 0.3 ± 0.05 seconds per prediction. • The average absorption of the top cell increased in the UV-vis region (650-800 nm) up to 93.4%. • The J sc in the top cell increased by 2 mA / c m 2 by integrating the optimized metasurface. [ABSTRACT FROM AUTHOR]

Abstract Multi-junction solar cells are known to have a considerably increased efficiency potential over their typical single junction counterparts. In order to produce low cost and lightweight multi-junction devices, the availability of suitable narrow (<1.1 eV) bandgap bottom cells is paramount. A possible absorber for such a bottom cell is the Cu(In,Ga)Se 2 (CIGS) compound semiconductor, one of the most efficient thin film materials to date. In this contribution we report on the RbF post deposition treatment of narrow bandgap CIGS absorbers grown with a single bandgap grading approach. We discuss the necessary deposition conditions and the observed improvements on solar cells performance. A certified record efficiency of 18.0% for an absorber with 1.00 eV optoelectronic bandgap is presented and its suitability for perovskite/CIGS tandem devices is shown. Highlights • RbF post deposition conditions for low bandgap CIGS are investigated. • A maximal efficiency of 18.0% is achieved for an optoelectronic bandgap of 1.00 eV. • Projections for 23.5% tandem with a NIR transparent perovskite top cell are given. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSC) based on organic–inorganic materials are considered to be the most promising photovoltaic technology because of their meteoritic progress in power conversion efficiency (PCE) from 3.8% to 22% to address the increasing energy demand, greenhouse gasses, and depleting fossil fuels. The breakthrough regarding the device efficiency and reproducibility is a combination of compositional engineering of cations, anions, the presence of a non-stoichiometric excess of lead iodide, and solvent engineering to grow over-layer of perovskite on top of the mesoporous layer. The last few years have witnessed a breakthrough in mixed-halide perovskite solar cells where the perovskite layer sandwiched in between selective charge extracting materials for the highly efficient solar cells. However, guidelines for interface engineering, essential for photovoltaic and optoelectronic applications, are still missing. This review will derive rationale understanding for future device development, revealing the exact interfacial processes for photovoltaic and optoelectronic Applications and their perspectives. [ABSTRACT FROM AUTHOR]

Highlights • The devices fabricated after the CdCl 2 treatment exhibited a diode-like behavior. • CdS cap on Cd-Zn-Te acts as a barrier to prevent Zn loss during the CdCl 2 treatment. • Retained Zn in the bulk of Cd-Zn-Te with chlorine decorating the grain boundaries. • Band gap maintained after the CdCl 2 treatment on Cd-Zn-Te fitted with CdS cap. • Method can be extended to other high band gap alloys of CdTe (Cd-Mg-Te, Cd-Mn-Te). Abstract A major challenge in the fabrication of high band gap II–VI polycrystalline solar cells is to preserve the original composition of the absorber after the CdCl 2 activation treatment. In this study, a method is demonstrated to maintain the Cd-Zn-Te alloy absorber composition during its exposure to the CdCl 2 treatment. A thin film of CdS was applied as a barrier on the back surface of the high band gap polycrystalline Cd (1−x) Zn x Te (x = 20% by atomic ratio, corresponding band gap 1.72 eV) before the CdCl 2 treatment. Using transmission electron microscopy and energy dispersive spectroscopy, it was observed that the composition of Cd-Zn-Te was maintained after the CdCl 2 treatment. The devices fabricated after removing the thin film of CdS, exhibited diode-like behavior. A significant increase in the quantum efficiency near the short wavelength region was observed, and the band gap of Cd (1−x) Zn x Te was maintained. [ABSTRACT FROM AUTHOR]

Perovskite/silicon-heterojunction solar cell is a very promising cell structure for using the solar spectrum efficiently and hence improving the energy conversion efficiency. However, perovskite solar cell based on solution technique requires the planar silicon-heterojunction bottom solar cell, which needs a different fabrication process from the textured substrate. In this paper, we developed the high performance planar silicon-heterojunction solar cell by introducing a novel design for the n-type back field and p-type emitter. The results indicate that a wide bandgap and low refractive index nc-SiO x :H for back field improves the open-circuit voltage, fill factor and short-circuit current density by the increased near-infrared long wavelength response. In addition, a nc-Si:H buffer layer between the a-Si:H passivation layer and p-nc-SiO x :H emitter increases the crystallinity in the emitter and then improves device performance further. Combining the developed nc-SiO x :H back field and p-nc-SiO x :H emitter, we achieved an efficiency of 18.77% (Certified 19.1%) on a smooth c-Si wafer. Realization of perovskite/silicon monolithic tandem solar cells with an over 1.7 V output voltage shows the potential application for solar to fuel generation and it also proves that the above strategies are very effective for improving the performance of bottom cell in the tandem solar cells. [ABSTRACT FROM AUTHOR]

In this work, we report systematic studies on improving the optical and electrical properties of four-terminal perovskite/c-Si tandem solar cells. Light harvesting power of the device is significantly enhanced due to the complementary absorption spectra of the perovskite and c-Si absorber materials. To obtain high power conversion efficiency (PCE) for the device, careful engineering of optoelectronic properties of the devices are accomplished through: 1. Oxygen annealing treatment for reducing defect density of perovskite materials; 2. Optical engineering of the transparent electrode (MoO 3 /Au/MoO 3 ) to obtain high transmission at long wavelengths for the tandem solar cell applications; and 3. Enhancement of light harvesting power achieved by using the novel biomimicking elastomeric petals as the light trapping layer. The individual perovskite solar cell (PSC) with MoO 3 /Au/MoO 3 electrode with or without light trapping layer yields an average PCE of 16.6% and 16.0% respectively. By combining c-Si bottom cell with perovskite top cell mechanically, an overall PCE of 22.4% is achieved for the averaged value, which is a promising result for future development of perovskite based tandem solar cells. [ABSTRACT FROM AUTHOR]

Electron transport medium (ETM) is one of the most important components determining the photovoltaic performance of organic-inorganic halide perovskite solar cells (PSCs). Among the metal oxide semiconductors, anatase (TiO 2 ) is the most common material used as ETM in PSCs to facilitate charge collection as well as to support a thin perovskite absorber layer. Production of conductive crystalline TiO 2 requires relatively higher temperatures (400–500 °C) which limits its application to glass substrates coated with fluorine tin oxide (FTO) as other tin oxides (e.g. indium tin oxide) degrade at temperatures above 300 °C. Furthermore, this renders it unsuitable for flexible devices, often based on low-temperature flexible plastic substrates. Pure tin oxide, one of the earliest metal oxide semiconductors, is often used in myriad electronic devices and has shown outstanding characteristics as an ETM in PSC systems. Thus, tin oxide can be considered a viable alternative to TiO 2 due to its excellent electron mobility and higher stability than other alternatives such as zinc oxide. This review article gives a brief history of ETMs in PSC systems and reviews recent developments in the use of tin oxide in both pure and composite form as ETMs. Efficiencies of up to 21% have been reported in tin oxide based PSCs with photovoltages of up to ~1214 mV. [ABSTRACT FROM AUTHOR]

This study examines the growth condition to obtain a single-phase Cu(In,Ga)S 2 (CIGS) chalcopyrite film epitaxially grown by coevaporation on a GaP/Si(001) pseudo-substrate. In particular, we report the structural differences between KCN-etched Cu-rich and Cu-poor CIGS films coevaporated on GaP/Si(001) by 1-stage process. The Cu-poor CIGS film consists of at least three phases; the main crystal is found to be chalcopyrite-ordered, coexisting with In-rich CuIn 5 S 8 , and CuAu-ordered CuInS 2 , all sharing epitaxial relationships with each other and the GaP/Si(001) pseudo-substrate. On the other hand, the Cu-rich CIGS film is single-phase chalcopyrite and displays sharper X-ray diffraction peaks and a lower density of microtwin defects. The elimination of the secondary CuAu-ordered phase with Cu excess is demonstrated. In both films, the chalcopyrite crystal exclusively grows with its c-axis aligned with the out-of-plane direction of Si[001]. This study confirms prior findings on the thermodynamics of Cu–In-Ga-S and the stability of secondary phases. [Display omitted] • Epitaxy of Cu(In,Ga)S 2 on GaP/Si(001). • Structural differences in Cu-poor and Cu-rich films. • Cu excess eliminates CuAu-ordered phase. • Reduction in microwtin density in Cu-rich films. • Potential for Cu(In,Ga)S 2 /Si tandem cells. [ABSTRACT FROM AUTHOR]

Wide-bandgap perovskites solar cells (PSCs) are vital as top cells in perovskite-based tandem solar cells (TSCs). However, poor band alignment with the charge transport layer and unwanted parasitic absorption in the top semitransparent-PSC (ST-PSC) are major factors limiting the power conversion efficiency (PCE) of TSCs. Herein, we present a compact-porous nickel oxide (cp -NiO x) hole-transport layer (HTL) sequentially fabricated using a sol-gel suspension and colloidal suspension of highly crystalline NiO x. The cp -NiO x film exhibited enhanced transparency, mesoporous surface morphology, and better energy band alignment with a 1.68 eV perovskite film for fabricating highly near-infrared transparent (∼92 % (@800–1200 nm)) ST-PSCs. The best cell achieved a PCE of 15.9 %. In addition, a four-terminal perovskite/silicon TSC based on the c p -NiO x HTL achieved an outstanding PCE of ∼26.0 %. The tailored energy band structure and reduced parasitic absorption in the near-infrared region of the ST-PSCs based on the cp -NiO x HTL enabled fabrication of highly efficient inverted ST-PSCs for perovskite/silicon TSCs. [Display omitted] ● The cp -NiO x films were consecutively fabricated using spin-coating and spray-coating techniques. ● The cp -NiO x /perovskite interface possesses lower buried defects. ● The cp -NiO x films have mesoporous surface morphology and excellent surface properties for perovskite film formation. ● Wide-bandgap perovskite solar cell consisting cp -NiO x HTL yielded PCE of ∼15.95 % and NIR transmittance (>92 %). ● 4T perovskite/silicon tandem cells based on the cp -NiO x HTL yielded a PCE of 26.0 % with superior stability. [ABSTRACT FROM AUTHOR]

First-principle investigations indicate that calculated and experimental lattice constant of rock-salt Ba 2 GdSbO 6 (BGSO) double perovskite show close proximity. The BGSO is a mechanically stable, highly rigid, elastically anisotropic and brittle crystal with high melting temperature. Spin-polarized band structures predict its indirect band-gap semiconductor nature. Partially filled 4f and 5d states of Gd make BGSO strongly ferromagnetic and hence suitable for magnetic data storage device. Holes are the majority carriers in BGSO due to positive Seebeck coefficient. Large electronic figure-of-merit projects BGSO as a promising thermoelectric material. Several thermodynamic parameters are also calculated in the present study. Calculated specific heat at constant volume follows the Debye's T3 and Dulong-Petit limit at very low and high temperature, respectively. Optical properties are calculated mainly in terms of complex dielectric function and other ancillary parameters. The indirect band-gap (>2.0 eV) semiconductor BGSO would have promising application in next generation low-cost tandem solar cells. [ABSTRACT FROM AUTHOR]

High-quality wide-bandgap perovskite films are a key component in constructing efficient tandem solar cells. Although the efficiency of perovskite tandem devices advances rapidly in recent years, the majority of wide-bandgap perovskite films are deposited by laboratory spin-coating, which greatly hinders their commercial viability. Here, we first show that the widely-used binary solvents (DMF:DMSO) in spin-coating are incapable of producing qualified wide-bandgap perovskite films by scalable methods. It is identified that dense and uniform wide-bandgap thin films can be deposited from single-solvent NMP by blade-coating, which is mainly related to the well-controlled crystallization kinetics enabled by the formation of stable intermediate adduct. Along with a rational passivation by constructing a 2D/3D layered heterojunction, inverted perovskite devices with a bandgap of 1.8 eV deliver a champion efficiency of 18.92 %. On this basis, monolithic perovskite-organic tandem solar cells with an efficient and robust interconnection layer of "SnO 2 /Au/PEDOT:PSS" are fabricated, yielding a high efficiency of 22.25 % along with an impressive open-circuit voltage of 2.1 V. These results demonstrate an important step toward scalable fabrication of monolithic perovskite-organic tandem solar devices. [Display omitted] • It is found that solvent plays an essential role in determining crystallization kinetics of scalable-coated wide-bandgap perovskite films. • NMP is identified as an ideal solvent to deposit high-quality wide-bandgap perovskite films due to the formation of stable intermediate adducts. • Wide-bandgap (1.8 eV) perovskite solar cells exhibit a high PCE of 18.92% along with a high V OC of 1.26 V. • Monolithic perovskite-organic tandem solar cells were constructed, yielding a champion efficiency of 22.25%. [ABSTRACT FROM AUTHOR]

Tandem technologies offer potential price reductions and higher efficiencies of PV modules. The high band gap nature of chalcogenides like CIGS, CZTS and AZTS makes them excellent materials for use on top of a Si base tandem cells. Nevertheless, along with the search for new technologies, there is also the concern about the environmental impact that its lifetime can cause. A comprehensive life cycle assessment for CIGS/Si, CZTS/Si and AZTS/Si tandem solar modules was not reported to date. This work compares the environmental impacts of Si and chalcogenide/Si tandem solar modules, assessing global warming potential, human toxicity potential (cancer and non-cancer effects), freshwater eutrophication potential, freshwater ecotoxicity potential, abiotic depletion potential and the energy payback time of these technologies. The results of this study show that compared with Si, CIGS/Si presents worse environmental impacts for most of the categories but, on the other hand, CZTS/Si and AZTS/Si present better outcomes for most of the impacts categories. We can also say that higher efficiency of these tandem technologies could potentially reverse that result. This LCA provides design advice for the R&D community, showing which structure has the best environmental outcomes and which processes should be optimized to achieve better results. [ABSTRACT FROM AUTHOR]

Recent development in band-gap engineering technology has lead researches in the field of tandem photovoltaic solar cells to examine the feasibility of low-dimensional multi-junction solar cell. This is achieved by the combination of only two materials with different band-gaps, piled vertically with different thicknesses. It is theoretically possible to tailor a set of effective band-gaps responding to the requirement of tandem solar cells with a maximum efficiency. In the present work we investigate the potential of tandem solar cells based on GaPAs/GaInAs multiple quantum well structure. Efficiency limit has been previously calculated using the detailed balance principle for multi-junction solar cells. Adjusting the number of wells and their widths and barrier depth gives the possibility of varying the effective band-gap. Numerical resolution of Schrodinger equation for GaPAs/GaInAs multiple quantum well demonstrates the potential of this III–V compound to achieve a wide range of effective band-gaps varying from 2.27 to 0.70 eV. However, this material could be used to manufacture low-dimensional tandem solar cells and can achieve tandem solar cells up to six sub-cells, that can yield an efficiency limit up to 59% for series constrained AM 1.5 global radiation. [ABSTRACT FROM AUTHOR]

We present a modeling framework to quantify current density losses and determine optimization steps for four-terminal tandem solar cells, which consist of a high-bandgap thin-film top cell and an industrial-type Si wafer bottom cell. We demonstrate the framework on the example of a 21.3% efficient stacked four-terminal GaAs/Si tandem solar cell. In a first step, we develop an optical model for stacked tandem configuration and carry out the current loss analysis for this tandem device. Photon absorption in the tandem is broken down into different channels. All parasitic absorptions that do not contribute to current generation are considered part of a loss channel. In a second step, we quantify the potential current gains from single-parameter optimizations, the redistribution of photon losses into other channels, and the synergistic gains that can be achieved by co-optimization. Finally, using the simulation model, we are able to determine the best sequence of optimizing the short-circuit current density in the GaAs/Si tandem solar cell to possibly achieve 37.8 mA/cm 2 with experimentally feasible parameters. [ABSTRACT FROM AUTHOR]

Replacing the present-day commercial single junction silicon (Si) solar cells with low cost, high efficiency solar cells is imperative, in order to compete with other existing energy technologies. Many research groups have looked into using III–V materials, tandem junction solar cells and thin-film technologies to reach higher efficiencies. However, many of these techniques involve expensive materials or costly manufacturing processes. In this research, we focus on a tandem junction solar cell design that is based on a thin-film perovskite top cell and wafer-based Si bottom cell. In order to analyze the performance of the tandem cell, an analytical model is needed to compute the quantum efficiency and characteristic solar cell data. The highly versatile Matlab-based analytical model presented in this work is capable of modeling different kinds of tandem cells based on a variety of solar absorber combinations. The model allows user to adjust input parameters, such as reflectivity, material thickness, donor and acceptor densities, and carrier lifetimes in order to optimize the quantum efficiency, maximum power output, open circuit voltage, and short circuit current quantities of the cell. Using this analytical model, we were able to design a perovskite and black Silicon (bSi) tandem cell, which reached an efficiency of greater than 30%. [ABSTRACT FROM AUTHOR]

Recent developments have unlocked the main issues arising from the combination of III-V and silicon and have opened a new way to fabricate tandem solar cells. In this study we provide a detailed analysis of III-V/epi-SiGe tandem devices performance using opto-electrical models and parameters acquired from previous experimental realizations of single junction devices. At first, we present the validation of our top and bottom cells models by comparison with previously published solar cells. The analysis of the current matching and the impact of the Al content in AlGaAs absorber on the open circuit voltage is performed on a very wide range of thickness and Al content. The optimal configurations for tandems with thin film absorbers are found with an empirical expression. This expression relates the required bottom absorber thickness to the Al content for current matching in a flat tandem device. Low-temperature epitaxial SiGe growth on III-V materials is an inverted growth technique, meaning that the last material grown is the Si(Ge) bottom cell. We can thus easily texture the back of the bottom cell for higher photon absorption. The proposed nanostructurization of the back reflector shows that, to reach the same efficiency, only half of the thickness is required if a 2D grating is combined with a silver reflector. The detailed influence of the bulk and interface electrical quality in the epi-SiGe bottom cell is also assessed. Finally, the prediction of the tandem device performance according to different realistic scenarios is presented. [ABSTRACT FROM AUTHOR]

• High efficiency all perovskite tandem solar cell is modelled for the first time with MAGeI 3 and K 2 PtBr 6 as the absorber layers of two sub cells. • A DFT study on the MAGeI 3 and K 2 PtBr 6 provided optoelectronic properties for device modelling. • A high PCE of 33.10 % is achieved for the all perovskite 4-T device configuration. • A PCE of 24.30 % is achieved for the all perovskite 2-T tandem configuration. This study reports for the first time a detailed device modelling and simulation of an all-perovskite tandem solar cell consisting of methyl ammonium germanium iodide (MAGeI 3) and dipotassium hexabromoplatinate (K 2 PtBr 6) as the light absorber materials for the two sub cells by employing SCAPS 1D simulation tool. The input parameters of perovskite materials including the bandgap, band structure, density of states (DOS) and other relevant optical parameters are estimated by density functional theory (DFT) employing WIEN2k software. The estimated bandgaps of MAGeI 3 and K 2 PtBr 6 are found to be 1.82 eV and 1.1 eV respectively, when PBEsol exchange correlation functional of GGA is employed for calculations. The device when modelled in the 2-terminal (2 T) monolithic configuration provides a power conversion efficiency (PCE) of 24.30 %, by inserting a recombination layer made of indium doped tin oxide (ITO) to establish the current matching condition between the top and bottom cells. On the other hand, the device when modelled in the 4 terminal (4 T) stacked layer configuration provides a PCE of 31.68 % when the filtered spectrum is employed as the input solar spectrum for bottom sub cell with K 2 PtBr 6 as absorber material. Further optimization of the input parameters of perovskite, ETL and HTL enhances the PCE of 4-T tandem architecture to 33.10 %. [ABSTRACT FROM AUTHOR]

Wide-bandgap perovskite is considered an ideal absorber for the top component cell of a tandem configuration, in addition to having proven advantageous for indoor light conversion and semitransparent solar cells. In this work, we demonstrate an ambient aging process that appears to further raise the performance of wide-bandgap perovskite solar cells. Systematic study shows that that secondary recrystallization arises during the aging process. The defect density is further attenuated by air passivation and the self-healing effect induced by halogen redistribution. As such, the nonradiative recombination in the perovskite films is suppressed, and the carrier lifetime is prolonged during the ambient aging. The champion wide-bandgap (E g =1.74 eV) perovskite solar cell delivered a power-conversion efficiency as high as 20.12%, coupled with a high open-circuit voltage of 1.27 V, which is among the highest values reported for this type of wide-bandgap solar cells. This work reveals the impact of the air aging process on the properties of perovskite films from various aspects and demonstrates a scalable post-treatment strategy capable of producing state-of-the-art semiconducting films. [Display omitted] • An ambient aging process raises the performance of wide-bandgap (E g =1.74 eV) PSCs. • Secondary recrystallization arises in wide-bandgap perovskite during the aging process. • The defect density is attenuated by air passivation and the self-healing effect is induced by halogen redistribution. • The champion wide-bandgap PSC delivered a PCE of 20.12%, among the highest values reported for this type of solar cells. [ABSTRACT FROM AUTHOR]

The Kesterite solar cells research landscape is at a crossroad and despite a much improved understanding of the limitations of this class of materials, the current performance deficit contrasts with the several other thin film technologies reaching conversion efficiency values well above 20%. It is more important than ever for the Kesterite community to collaborate directly or indirectly and data sharing is an essential building block in that regard. This work proposes a detailed set of modelling baselines and parameters, based on a consistent set of properties obtained with experimental devices made by our group. These parameters permit to accurately reproduce all photovoltaic figures of merits of reference experimental Kesterite cells with a relative accuracy of 1% or less. As a case study, and using optical modelling based on the transfer matrix method in complement, the potential of Kesterite materials in tandem devices with either a Perovskite or a Crystalline Silicon partner is evaluated. It is found that a moderate improvement of pure selenium CZTSe, feasible in the short to middle term, would realistically permit to use this material as bottom subcell in tandem with a Perovskite top cell and obtain efficiencies reaching the 30% threshold. On the other hand, using a Kesterite absorber in a top subcell with a silicon bottom subcell appears as particularly ambitious even when considering several important optimizations to the material, and it is believed that only an important breakthrough would render this material viable for such application. The complete set of material parameters, optical indices and modelling files are shared for the Kesterite community to use and build improve upon. [Display omitted] • Quantitative modelling of baseline pure Selenium and pure Sulfur Kesterite solar cells. • Application to tandem architecture by combining electrical and optical modelling. • Evaluation of improvement strategies offering a realistic outlook of Kesterite both as top and bottom subcell. • Complete and transparent data sharing for the community to use a common baseline in future modelling studies on Kesterite. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cell (DSSC) offers an efficient and easily implemented technology for future energy supply. Compared to conventional silicon solar cells, it provides comparable power conversion efficiency (PCE) at low material and manufacturing costs. DSSC materials such as titanium oxide (TiO 2 ) are inexpensive, abundant and innocuous to the environment. Since DSSC materials are less prone to contamination and processable at ambient temperature, a roll-to-roll process could be utilized to print DSSCs on the mass production line. DSSCs perform better under lower light intensities, which makes them an excellent choice for indoor applications. Due to the advancement of molecular engineering, colored and transparent thin films have been introduced to enhance the aesthetic values. Up to now, such benefits have attracted considerable research interests and commercialization effort. Here, this review examines advanced techniques and research trends of this promising technology from the perspective of device modeling, state-of-art techniques, and novel device structures. [ABSTRACT FROM AUTHOR]

Firstly, multi-fold subphthalocyanine (SubPc) homo-tandem cells were fabricated. When complementary absorbing SubPc and chloroaluminum phthalocyanine (ClAlPc) were used to prepare tandem cells, both short circuit current ( J SC ) and fill factor (FF) are significantly improved relative to the SubPc double tandem cell. 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI) as electron transporting layer (ETL) in the charge recombination zone (CRZ) achieves a much higher FF than bathocuproine (BCP) thus higher power conversion efficiency ( η PCE ) in both the normal and reverse tandem cells, ascribed to the matched energy levels, very smooth film surface, and ohmic contact with Ag interlayer. The effect of Ag interlayer thickness was also investigated. Ultrathin Ag layer with isolated clusters is helpful for obtaining higher photocurrent in both PTCBI and BCP based CRZs, originating from a flatter interface, less optical loss, and a plasmonic effect induced absorption enhancement of C 60 in bottom subcell. By optical modeling for current matching, the performance of normal tandem cell is improved, exhibiting a high open circuit voltage of 1.80 V and an overall η PCE of 3.49%. [ABSTRACT FROM AUTHOR]

Lattice matched and current matched GaAsP/SiGe tandem solar cells on Si have the potential of 40% conversion efficiency [8] . A corrected three-terminal tandem efficiency of 20.6% under 1× illumination has been achieved, a relative improvement of approximately 9% compared to the 18.9% efficiency reported previously. Current matching is realized under 2.1× illumination. This is achieved by improving the bottom cell structure, manipulating the bottom cell active area and adjusting the light spectrum during light IV measurements. This paper describes the design of the improved structure, a simplified fabrication process and a detailed current matching analysis of this tandem solar cell. Pathways to achieve the realistic efficiency of over 25% under 1× illumination and near 30% under 20× illumination are also discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Actively manipulated Ga growth profile for fabricating high-quality CIGS films on flexible PI substrates. • A reasonable GGI double grading with a large grain size could be accomplished at the same time. • A tiny amount of Ag-doping CIGS absorber could improve the flexible device's performance even more. • A champion efficiency of 21.56 % was achieved for an all-flexible 4 T perovskite/CIGS tandem solar cells. A tandem solar device is the most promising approach for overcoming the single-junction Shockley-Queisser limit, as it can also be manufactured on flexible substrates and is cost-effective and lightweight for a wider range of applications. As is well known, developing high-performance flexible CIGS solar cells is a crucial prerequisite for realizing high-quality tandem devices. To increase the performance of flexible CIGS solar cells, a unique Ga growth profile was created and built in this study, which co-evaporated with Cu and Se in the second step of the well-known "three-step co-evaporation technique." The best flexible CIGS solar cell with a thickness of around 1.6 μm achieves an impressive efficiency of 18.93 %, not only because a decent double GGI grading can be made, but also the overall grain can be enlarged, which is always difficult to combine well in the past. Finally, an all-flexible 4-terminal (4 T) perovskite/CIGS tandem device was fabricated and demonstrated over 21.5 % efficiency, the highest efficiency of all-flexible perovskite/CIGS tandem solar cells reported in the literature to the best of our knowledge. This study could pave the way for the fabrication of high-quality CIGS thin films and solar devices on flexible polymer substrates. [ABSTRACT FROM AUTHOR]