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As the balance of system cost of photovoltaic (PV) installations governs the competitiveness of PV device market, next‐generation solar cells desire substantially enhanced power conversion efficiencies (PCEs). The single‐junction perovskite and Si solar cells have demonstrated PCEs beyond 26% and 25%, respectively. The tandem configuration has crossed the threshold posed by the shockley queisser limit by demonstrating the 33.9% PCE. However, the unresolved issues in the perovskite community from a stability perspective pose challenges for realizing highly efficient and stable perovskite–Si tandem solar cells (TSCs). This review highlights the current status of perovskite–Si TSC from a stability perspective besides elucidating the degradation mechanisms at the perovskite–Si at the cell and module level. A highly efficient perovskite–Si TSC needs optimization keeping view the specific requirements for tandem configuration like strain, current matching, and bandgap optimization between the top perovskite and bottom Si subcell. Various stressors affecting the efficiency of the perovskite–Si module, namely, reverse bias and hot spot formation, and delamination, highlight valuable insight to develop future strategies for the perovskite–Si TSC. Stability regimes for the single‐junction perovskite solar cell can provide the essential stepping stone but, modified stability regimes are inevitable. [ABSTRACT FROM AUTHOR]

The procedures for the power rating of tandem‐cell‐based concentrator photovoltaic (CPV) modules defined in the international standard IEC 62670‐3 are adapted to the requirements of tandem‐cell‐based flat plate PV modules. The adjusted procedure describes how to translate outdoor measured PV current–voltage characteristics to standard test conditions (STC): 1000 W/m, 25°C cell temperature, AM1.5g spectral conditions. In this work, we describe how to obtain all required input parameters: thermal transient measurements to determine the module temperature coefficients, categorizing and filtering the prevailing spectral irradiance conditions using spectral matching ratios, and determining the 25°C module open‐circuit voltage from dark current–voltage curves. Three specimen PV modules (triple‐junction, III‐V on Silicon and III‐V on Germanium) have been measured for several months outdoors on a dual axis tracking unit at Fraunhofer ISE in Freiburg. In this work, we demonstrate that the CPV module power rating procedures in IEC 62670‐3 are also—in a modified form—to be recommended for the outdoor rating of tandem‐cell‐based flat plate PV modules. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting, and carbon dioxide (CO 2) utilization devices have attracted immense attention as sustainable technologies for the generation of hydrogen (H 2) fuel and value-added chemicals feedstock. Among numerous semiconductors, bismuth vanadate (BiVO 4) has emerged as a promising photoanode owing to its fascinating features such as high chemical stability, straddling band alignment with water redox levels, eco-friendly, and cost-effectiveness. However, sluggish oxidation kinetics, photo-corrosive nature, low electronic conductivity, and short carrier diffusion length limit its commercialization on the PEC horizon. To mitigate these inadequacies, several strategies have emerged such as novel heterojunctions, doping with unique materials, interface modulation, morphology, facet orientation, co-catalyst loading for surface engineering, etc. to realize the outstanding cost-to-efficiency ratios and long-term stability of PEC devices. The review highlights the recent advancement in BiVO 4 -based photoanodes in last five years (2018–2022) and their utilization in the single absorber and unexplored tandem PEC systems towards boosted water splitting and CO 2 reduction. A discussion on theoretical studies of BiVO 4 -based PEC systems elucidates the microscopic mechanism of promotion effect of the bulk/interface/surface strategies on surface catalysis as well as interfacial charge transfer in boosting oxidation kinetics. Moreover, this review addresses the versatility of the BiVO 4 -based photoanode for the novel yet commercially viable PEC applications. This review will provide a broad avenue in designing highly durable, and scalable BiVO 4 -based systems toward various PEC energy conversion devices. [Display omitted] • BiVO 4 is a promising photoanode for PEC water splitting and CO 2 reduction. • Recent progress in the various strategies to improve PEC performance is reviewed. • BiVO 4 -based tandem water splitting and CO 2 reduction systems are emphasized. • Future outlooks are addressed with associated challenges. [ABSTRACT FROM AUTHOR]

With the success of silicon (Si) solar cell technology, research and development on higher efficiency multijunction solar cells is gaining much attention. Tandem cells with a perovskite top cell and a Si bottom cell show particular potential. However, the optical modeling of such devices is complicated by the broad range of length scales involved; the optically thin layers and nanoscale features of a perovskite solar cell require some version of wave optics or even full field electromagnetic (EM) calculations, while the micrometer scale structuring and large dimensions of Si cells are much more manageable using geometrical (ray) optics. In the present work, a method for combining EM and ray optical calculations is developed and described in detail, with examples provided in the software Comsol Multiphysics. For regions with thin films or nanoscale features, EM wave calculations are performed using the finite element method. These calculations provide the phase and amplitude of the waves diffracted into different orders, of which only the regular reflection and transmission are typically of relevance for nanoscale periodicity. In the ray optics simulation, the corresponding regions are implemented as diffracting interfaces, with deterministic transformations of the Stokes vector components according to the EM wave calculations. Meanwhile, the absorbed intensity of intersecting rays is recorded. The method is applied to separate perovskite and Si solar cells and to a few tandem solar cells of relevance for two- versus four-terminal configurations. Corrections for strongly absorbing media in the ray tracing algorithm, which use generalized versions of the Fresnel coefficients, Snell's law and the Beer-Lambert law, are also evaluated. In a typical Si solar cell with a front surface structure of inverted pyramids, such corrections are found to reduce the absorption by up to 0.5 percentage units compared to a conventional ray tracing calculation. The difference is concluded to originate mainly from reduced absorption rates of inhomogeneous waves, rather than from enhanced escape probabilities for (quasi-) trapped rays at the Si front surface. The method is further applied to evaluate the effects of a plasmonic nanoparticle array, embedded in a perovskite solar cell stack that is located directly on the microstructured Si surface. [ABSTRACT FROM AUTHOR]

As perovskite photovoltaics (PV) advance from the laboratory to commercial prototypes, their accurate and reliable performance testing is becoming increasingly important. The well‐documented dynamic response of perovskite solar cells to an external applied voltage has led to the development of steady‐state performance measurement methods; however, these methods have not been widely adopted by the perovskite PV community. A key reason for this is that steady‐state measurement methods take tens of minutes to complete, as opposed to conventional "fast" current–voltage (I–V) measurements usually lasting a few seconds. Fast I–Vs arise from a snapshot, almost always not a steady‐state condition of the device; however, given their widespread use, the question arises: how do performance parameters of perovskite PV compare when measured with fast I–V and with a steady‐state method? Results compiled from approximately 200 perovskite PV cells, including single junction, and two‐terminal perovskite–perovskite and perovskite–Si tandems, show that fast I–Vs can provide a useful measure of the open‐circuit voltage of the devices, while the short‐circuit current and the overall efficiency can be widely misestimated. The implications of these findings on performance testing protocols are discussed and possible options for fast and accurate testing of perovskite PV are proposed. [ABSTRACT FROM AUTHOR]

The development of an efficient conversion system to transform solar energy into chemical energy, such as renewable hydrogen, is a promising way to overcome energy problems. Photoelectrochemical (PEC) water splitting is a promising means of obtaining renewable hydrogen directly from water utilizing sunlight. Recent reports have demonstrated that a PEC cell with a tandem configuration (tandem cell) has the potential to realize a high solar‐to‐hydrogen (STH) energy conversion efficiency by solar water splitting. However, there are still many obstacles to the development of practical and cost‐effective tandem cells. In particular, development of efficient photoanodes for the oxygen evolution reaction (OER) is a prerequisite for improving the STH efficiency. Herein, recent progress in developing (semi)transparent photoanodes for the OER, such as Fe2O3, BiVO4, and Ta3N5, is described based on the topics of preparation methods, semiconductor properties, and PEC performance. In addition, the strategies for enhancing the STH efficiency of tandem cells consisting of (semi)transparent photoanodes conjugated with photovoltaic (PV)‐based cathodes are summarized. This Review is expected to provide guidelines for the future development of tandem cells capable of highly efficient and stable water splitting.

• A first working monolithic CZTS/Si tandem cell is presented and characterized. • A MoS 2 /FTO/ZnO intermediate contact between top and bottom cells is developed. • Limiting factors of this device are addressed and investigated to overcome them. Earth abundant Cu 2 ZnSnS 4 (CZTS) semiconductor can find a promising application as wide-bandgap top cell absorber in CZTS/Silicon tandem devices. The coupling between the top and the bottom cells in a monolithic device requires the development of a proper intermediate connection able to ensure: (i) high transparency in the infrared region (ii) good electric contacts and (iii) good chemical stability under thermal treatments used for the CZTS growth, in order to prevent elements interdiffusion and silicon degradation. To this purpose, some multilayered structures based on MoS 2 and different Transparent Conductive Oxides (TCOs) were tested as intermediate connection in CZTS/Silicon tandem devices. The first working monolithic tandem cell, with open circuit voltage of about 950 mV and an efficiency of 3.5%, was obtained using a MoS 2 /FTO/ZnO trilayer structure as intermediate contact between the top and the bottom cells. Some limiting factors of this device were addressed and investigated in order to increase the tandem cell efficiency. [ABSTRACT FROM AUTHOR]

A series of zinc tetraphenylporphyrin photosensitizers furnished with three different anchoring groups, benzoic acid, phenylphosphonate and coumarin-3-carboxylic acid, were prepared using 'click' methodology. All three gave modest performances in liquid junction devices with I3–/I– as the electrolyte. The distinct spectroscopic properties of the porphyrins allowed a detailed investigation of the adsorption behaviour and kinetics for charge transfer at the NiO‖porphyrin interface. The adsorption behaviour was modelled using the Langmuir isotherm model and the phosphonate anchoring group was found to have the highest affinity for NiO (6.65 × 104 M−1) and the fastest rate of adsorption (2.46 × 107 cm2 mol−1 min−1). The photocurrent of the p-type dye-sensitized solar cells increased with increasing dye loading and corresponding light harvesting efficiency of the electrodes. Coordinating the zinc to a pyridyl-functionalized fullerene (C60PPy) extended the charge-separated state lifetime from ca 200 ps to 4 ns and a positive improvement in the absorbed photon to current conversion efficiency was observed. Finally, we confirmed the viability of electron transfer from the appended C60PPy to phenyl-C61-butyric acid methyl ester, a typical electron transporting layer in organic photovoltaics. This has implications for assembling efficient solid-state tandem solar cells in the future. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'. [ABSTRACT FROM AUTHOR]

Over recent decades, the possibility of using solar power as an energy source has been limited by the implementation costs and the net conversion efficiency. Additionally, in comparison with the traditional sources, solar energy cannot produce energy for all the twentyfour hours of the day, which increases the costs of the source, due to the need of a backup system. Therefore, this paper studies the effect of combining different types of semiconductors as Si, Ge, AlGaAs and GaAs, focusing on how the conversion efficiency can be improved. In order to perform this, a multilayer solar cells analysis across the study of the quantum efficiency, which quantifies the amount of energy lost in the power conversion process, is implemented. In order to develop the required study PC1D software, specialized in simulate semiconductor's behavior based on its physiochemical properties, which gives the possibility to create different layers of solar cells is utilized. From the data acquired of the simulated cells, the paper presents the electrical results starting from a cell of one layer to a cell of four layers with the aim of establishing the relation between the number of layers and the net conversion efficiency under standard environmental conditions. [ABSTRACT FROM AUTHOR]

Fabrication of wide band-gap ( E g ) CuGaSe 2 (CGSe) thin film solar cells with large area uniformity and good reproducibility is difficult, which is crucial for tandem cells. In this work, a method was proposed and investigated to overcome this problem. CGSe solar cells were fabricated by sputtering from a ternary CGSe target and post selenization treatment at different temperatures. After selenization, the CGSe grains grow up gradually, and the copper-poor and selenium-rich CGSe absorbers are obtained successfully. The X-ray diffraction peaks are all corresponded to CGSe phase. As the temperature increases from 530 to 570 °C, the average efficiency increases from 1.57% to 3.11%. When the temperature reaches 590 °C, the efficiency drops to 2.38%. The champion device obtained at 570 °C shows an E g of 1.66 eV and an efficiency of 3.21%, which indicates the potential for the top cell in tandem solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Using dual‐photoelectrode photoelectrochemical (PEC) devices based on earth‐abundant metal oxides for unbiased water splitting is an attractive means of producing green H2 fuel, but is challenging, owing to low photovoltages generated by PEC cells. This problem can be solved by coupling n‐type BiVO4 with n‐type Bi4V2O11 to create a virtual p/n junction due to the formation of a hole‐inversion layer at the semiconductor interface. Thus, photoelectrodes with high photovoltage outputs were synthesized. The photoelectrodes exhibited features of p‐ and n‐type semiconductors when illuminated under an applied bias, suggesting their use as photoanode and photocathode in a dual‐photoelectrode PEC cell. This concept was proved by connecting a 1 mol % W‐doped BiVO4/Bi4V2O11 photoanode with an undoped BiVO4/Bi4V2O11 photocathode, which produced a high photovoltage of 1.54 V, sufficient to drive stand‐alone water splitting with 0.95 % efficiency. [ABSTRACT FROM AUTHOR]

We report the synthesis of three new push-pull dyes specially designed for the sensitization of mesoporous p type semi-conductor NiO for the construction of p type dye sensitized solar cells (pDSC). Their structure stems from the conjugation of the well-known tris(carboxy-arlyamine) anchoring moiety to a benzothiadiazole acceptor through a fluorene ( PP1 ) or thiophene-fluorene linker ( PP2 ). Appending a NDI secondary acceptor onto PP2 yielded a dyad ( PP2-NDI ). The push-pull structure is here particularly adapted to the sensitization of p-type semi-conducting materials. All three dyes were investigated by spectroscopic and electrochemical techniques, and their electronic properties were modelled by TD-DFT. In all cases, the new sensitizers exhibit adequate absorption features (spanning from 400 nm to 600 nm, extinction coefficients between 20000 and 27000 M −1 cm −1 ) and their thermodynamic parameters are all in favor of efficient interfacial charge transfers involving NiO. pDSC were constructed with all three dyes; high photoconversion efficiencies (PCE) were reached, especially in the case of dyad PP2-NDI (Jsc = 5.90 mA/cm 2 , Voc = 143 mV, FF = 33.8%, PCE = 0.29%), due to a combination of outstanding electronic properties and increased charge separation state lifetime. Tandem DSC (tDSC) composed of a TiO 2 photoanode sensitized by the dye D35 and a NiO photocathode sensitized by PP2-NDI were assembled with two different electrolytes (I 3 − /I − or T 2 /T − based electrolytes). The latter gave PCE among the best ever reported for tDSC (Jsc = 5.90 mA/cm 2 ; Voc = 896 mV; FF = 63%, PCE = 2.80% in the case of the I 3 − /I − electrolyte, Jsc = 4.52 mA/cm 2 , Voc = 840 mV, FF = 60% and PCE = 2.27% for T 2 /T − based devices) unraveling the significance of the new dyes presented in this study. [ABSTRACT FROM AUTHOR]

Tandem photoelectrochemical water splitting cells utilizing crystalline Si and metal oxide photoabsorbers are promising for low-cost solar hydrogen production. This study presents a device design and a scalable fabrication scheme for a tandem heterostructure photoanode: p+n black silicon (Si)/SnO2 interface/W-doped bismuth vanadate (BiVO4)/cobalt phosphate (CoPi) catalyst. The black-Si not only provides a substantial photovoltage of 550 mV, but it also serves as a conductive scaffold to decrease charge transport pathlengths within the W-doped BiVO4 shell. When coupled with cobalt phosphide (CoP) nanoparticles as hydrogen evolution catalysts, the device demonstrates spontaneous water splitting without employing any precious metals, achieving an average solar-to-hydrogen efficiency of 0.45% over the course of an hour at pH 7. This fabrication scheme offers the modularity to optimize individual cell components, e.g., Si nanowire dimensions and metal oxide film thickness, involving steps that are compatible with fabricating monolithic devices. This design is general in nature and can be readily adapted to novel, higher performance semiconducting materials beyond BiVO4 as they become available, which will accelerate the process of device realization. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting, which is a type of artificial photosynthesis, is a sustainable way of converting solar energy into chemical energy. The water oxidation half-reaction has always represented the bottleneck of this process because of the thermodynamic and kinetic challenges that are involved. Several materials have been explored and studied to address the issues pertaining to solar water oxidation. Significant advances have recently been made in the use of stable and relatively cheap metal oxides, i.e., semiconducting photocatalysts. The use of BiVO4 for this purpose can be considered advantageous because this catalyst is able to absorb a substantial portion of the solar spectrum and has favourable conduction and valence band edge positions. However, BiVO4 is also associated with poor electron mobility and slow water oxidation kinetics and these are the problems that are currently being investigated in the ongoing research in this field. This review focuses on the most recent advances in the best-performing BiVO4-based photoanodes to date. It summarizes the critical parameters that contribute to the performance of these photoanodes, and highlights so far unresolved critical features related to the scale-up of a BiVO4-based PEC water-splitting device. [ABSTRACT FROM AUTHOR]

A photoelectrochemical (PEC) cell composed of a WO 3 /dye-sensitized solar cell (WO 3 /DSSC) and copper oxide (Cu x O, where x =1 and 2) wire arrays as a dual-absorber photoanode and cathode, respectively, is demonstrated as a stand-alone, durable device for CO 2 photoconversion. The Cu x O wire arrays, which have high surface-to-volume ratios, exhibit promising electrocatalytic activity for CO 2 conversion to CO at Faradaic efficiencies of ~80% and ~60% at E=−0.2 and −0.4 V vs . RHE, respectively, and H 2 production is minimized at a Faradaic efficiency <~20% in the potential range between −0.2 and −1.0 V vs . RHE. The single-absorber cell of a WO 3 photoanode and Cu x O wire array cathode couple (WO 3 -Cu x O) requires a minimum overpotential of ~0.7 V to drive CO 2 conversion. For stand-alone CO 2 conversion, a DSSC is coupled to the WO 3 -Cu x O system. In the dual-absorber cell (WO 3 /DSSC-Cu x O), the long-wave band (λ > ca . 450 nm) passed through the semitransparent WO 3 film is absorbed by the dye-sensitized TiO 2 electrode of the DSSC. The WO 3 /DSSC-Cu x O shows a potential gain of ~0.7 V and is able to successfully drive CO 2 conversion on Cu x O and simultaneously oxidize water on WO 3 without an external power supply. In this stand-alone system, the primary CO 2 conversion product is CO, with a solar-to-chemical energy efficiency of ~2.5%; H 2 and formate are obtained with energy efficiencies of 0.7% and 0.25%, respectively, in 5 h (overall efficiency ~3.45%). Neither CO 2 conversion product nor H 2 is found using the single-absorber system. [ABSTRACT FROM AUTHOR]

Fluctuational electrodynamics and minority carrier diffusion equations are applied to evaluate the electric power output of a near-field tandem thermophotovoltaic (TPV) system with a bulk tungsten emitter (at 1500 K) and InGaSb/InAs tandem cells (at 300 K). We give evidence of the superiority of the tandem TPV system over the single-junction TPV system in the near-field regime because a tandem structure can harvest useful photons in a wider spectral range. It is also found that in comparison with the system with a bulk tungsten emitter, the practically achievable indium‑tin‑oxide (ITO) emitter and multilayer emitter could enhance the electricity output by a factor of 1.7 and 2.9 as a result of the supported surface plasmon resonances and hyperbolic modes, respectively. The conversion efficiency of the ITO emitter is 6% higher due to the suppression of the surface recombination loss, but the efficiency of the multilayer emitter is even 15% lower because of the heavy bulk recombination loss. These results highlight the possibilities to enhance the performance of the near-field tandem TPV systems via optimizing the radiative absorption distribution in the tandem cells, which is paramount important for the design and improvement of near-field tandem TPV systems. • The performance of a near-field tandem TPV system is theoretically investigated. • The near-field tandem TPV system is superior to the single-junction one. • The impacts of surface plasmonic resonance and hyperbolic modes are examined. • ITO and multilayer emitters can enhance electric power by 1.7 times and 2.9 times, respectively. • Physical mechanisms enabling higher or lower conversion efficiency are analyzed. [ABSTRACT FROM AUTHOR]

Large voltage losses are the main obstacle for achieving high efficiency in organic solar cells (OSCs). Here we construct ternary OSCs by introducing an asymmetric small molecule acceptor AITC into PBDB-TCl : BTP-eC9 system and demonstrate the effectiveness in simultaneously decreasing energy disorder and non-radiative voltage losses. It is found that the introduction of AITC can modify domain size and increase the degree of crystallinity, which enhances open-circuit voltage and power conversion efficiency (19.1%, certified as 18.9%). Inspiringly, an output efficiency of 20.6% of the constructed tandem OSCs based on PBDB-TCl : AITC : BTP-eC9 ternary active layer output a recorded efficiency of 20.6% (certified as 20.3%), which is the highest value in OSCs field to date. This work demonstrates that decreasing the voltage losses by ternary strategy and constructing of tandem architecture are effective approaches towards improving photovoltaic performance., (© The Author(s) 2023. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd.)

We design a thermo-photovoltaic Tandem cell which produces high open circuit voltage ( V oc ) that causes to increase efficiency ( η ). The currently used materials (AlAsSb–InGaSb/InAsSb) have thermo-photovoltaic (TPV) property which can be a p – n junction of a solar cell, but they have low bandgap energy which is the reason for lower open circuit voltage. In this paper, in the bottom cell of the Tandem, there is 30 quantum wells which increase absorption coefficients and quantum efficiency (QE) that causes to increase current. By increasing the current of the bottom cell, the top cell thickness must be increased because the top cell and the bottom cell should have the same current. In the top cell, by increasing the thickness, absorption coefficients and quantum efficiency increase that causes to increase the current. Current increment is also the second factor that causes to increase overall efficiency. [ABSTRACT FROM AUTHOR]

Optical characteristics of the top and bottom cells in Cd 1− x Mg x Te/CuInSe 2 tandem solar cells with transparent ZnTe interconnection layer are investigated. Since the reflection coefficient is significantly attenuated in the case of Cd 1− x Mg x Te/ZnTe interface in comparison to the Cd 1− x Mg x Te/glass interface, the transmission through the monolithic top cell of the tandem can be calculated ignoring the oscillations. It has been shown that the short-circuit currents in the top and bottom solar cells match when the bandgap of Cd 1− x Mg x Te is in the range 1.67–1.70 eV. A good agreement between the measured and calculated periodic oscillations in the top cell transmittance has been demonstrated. It has been shown that the current matching can be achieved with a lower band gap Cd 1− x Mg x Te top-cell when borosilicate glass substrate is used, and also the short circuit current density is higher, compared to soda lime glass. [ABSTRACT FROM AUTHOR]

Silicon carbide/silicon rich carbide multilayers, aimed at the formation of silicon nanodots for photovoltaic applications, have been studied. The electrical properties have been investigated at the nano-scale by conductive Atomic Force Microscopy (c-AFM) and at macro-scale by temperature dependent conductivity measurements. The mixture is composed of highly conductive Si nanoclusters and moderately conductive SiC nanoclusters in a disordered matrix. The conduction mechanism takes place via band states induced by the disorder at the interface between nanodot clusters. Structural properties have been extracted by optical spectroscopy analyses. The results contribute to the understanding of the microscopical electronic mechanisms of the composite material, which is a candidate for third generation photovoltaics. [ABSTRACT FROM AUTHOR]

In this paper, the selective illumination approach is adopted to separately extract the shunt resistance of the individual subcells belonging to a tandem cell. The method relies on simple theoretical considerations and is based on the measurement of the current-voltage characteristic of the tandem cell by alternately keeping one of the subcells under dark conditions. Numerical simulations are employed to support the reliability of the technique, which is experimentally tested on micromorph devices deposited onto glass covered by a V-shaped transparent conducting oxide and subject to different thermal treatments. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Thin film tandem solar cells based on amorphous and microcrystalline silicon (a-Si:H/μc-Si:H) are employed as the cathode in a photoelectrochemical converter for solar water splitting. It is setup in such a way that the silver back contact of the cell is directly connected to the electrolyte and the light enters the cell through the glass substrate. This arrangement offers a number of distinct advantages compared to the conventional designs. The cathode is further optimized by the deposition of platinum nanoparticles to achieve higher conversion efficiencies. The front contact of the photovoltaic cell is connected to a standard platinum counter electrode in a three-electrode arrangement. Photon to current conversion efficiencies can reach up to 3% for our design, which has not been optimized to the requirements of the water splitting reaction, yet. The optimization of such tandem devices made from abundant silicon in combination with nanoparticle catalysts offers an affordable pathway for direct solar-to-fuel conversion devices in form of an artificial inorganic leaf. [ABSTRACT FROM AUTHOR]

We report a series-connected small molecule tandem photovoltaic cell utilizing two donors with complementary photovoltaic characteristics, lead phthalocyanine (PbPc) in the front subcell and boron subphthalocyanine chloride (SubPc) in the back subcell, to achieve both near infrared (NIR) response up to 1 μm and high open-circuit voltage ( V OC ) of more than 1.5 V in the same device. We find that the C 60 layer thickness in the front subcell has a critical impact on the overall optical structure and photovoltaic performance of the tandem device. By combining transfer matrix calculations with subcell-selective spectral measurements, we are able to tune the optical field distribution inside the active layers and increase the photocurrent outputs from both subcells, leading to EQE > 30% over the wavelength range 400 nm < λ < 900 nm. This optimized tandem cell exhibits J SC = (5.5 ± 0.1) mA/cm 2 , fill factor = 0.54, V OC = 1.53 V, and a power conversion efficiency of (4.5 ± 0.2)%. [ABSTRACT FROM AUTHOR]

Industry has previously established a 10% stable total module efficiency 1.1×1.3m2 thin film silicon tandem junction (TJ) module manufacturing baseline. A similar silicon TJ cell manufacturing process has been established, using a plasma enhanced chemical vapor deposition (PECVD) tool with an excitation frequency of 13.56MHz, which was modified to handle 30×30cm2 substrates. Extensive PECVD process window characterization was undertaken for the silicon layers that have the biggest impact on device performance. Single layer silicon on glass data and 1×1cm2 single junction and TJ solar cell data for amorphous intrinsic silicon and microcrystalline intrinsic silicon layers have been collected. Single layer characterization data for p-doped microcrystalline silicon oxide layer (μc-SiOx:H-p) for aluminum doped zinc oxide substrates is being presented, as well as solar cell data. The manufacturability of the μc-SiOx:H-p process is being considered. Finally, we present the best solar cell results obtained with the optimized PECVD process, as well as baseline performance data. [ABSTRACT FROM AUTHOR]

Abstract: Solar cells that convert sunlight into electrical power have demonstrated a large and consistent growth through several decades. The growth has spawned research on new technologies that potentially enable much faster, less costly and environmentally friendly manufacture from earth abundant materials. Here we review carbon based solar cells through a complete analysis of all the data that has been reported so far and we highlight what can be expected from carbon based technologies and draw scenarios of how it can be made of immediate use. [Copyright &y& Elsevier]

Microcrystalline silicon oxide (µc-SiO x :H) alloys prepared by plasma enhanced chemical vapor deposition (PECVD) represent a versatile material class for opto-electronic applications especially for thin-film and wafer based silicon solar cells. The material is a phase mixture of microcrystalline silicon (µc-Si:H) and amorphous silicon oxide (a-SiO x :H). The possibility to enhance the optical band gap energy and to adjust the refractive index over a considerable range, together with the possibility to dope the material p-type as well as n-type, makes μc-SiO x :H an ideal material for the application as window layer, as intermediate reflector (IR), and as back reflector in thin-film silicon solar cells. Analogously, μc-SiO x :H is a suitable material for p- and n-type contact layers in silicon hetero junction (SHJ) solar cells. The present paper gives an overview on the range of physical parameters (refractive index, optical band gap, conductivity) which can be covered by this material by variation of the deposition conditions. The paper focuses on the interdependence between these material properties and optical improvements for amorphous silicon/microcrystalline silicon (a-Si:H/µc-Si:H) tandem solar cells prepared on different substrates, such as Asahi (VU) and sputtered ZnO:Al. It gives a guideline on possible optical gains when using doped µc-SiO x :H in silicon based solar cells. As intermediate reflector in a-Si:H/µc-Si:H tandem cells µc-SiO x :H leads to an effective transfer of short circuit current generation from the bottom cell to the top cell resulting in a possible thickness reduction of the top cell by 40%. Within another series of solar cells shown in this paper a short circuit current density of 14.1mA/cm2 for an a-Si:H/µc-Si:H tandem solar cell with a µc-SiO x :H intermediate reflector is demonstrated. A SHJ solar cell on a flat (non-textured) wafer using p- and n-type doped µc-SiO x :H contact layers with an effective area efficiency of 19.0% is also presented. [ABSTRACT FROM AUTHOR]

Highlights: [•] PCE of 3.1% for the HB226 single-junction solar cell is among highest reported for shorter-wavelength-range. [•] Simple structured, high-efficiency organic tandem solar cell based on a merocyanine dye HB226 (PCE of 4.5%). [•] Performance improvement by ca. 50% in tandem device compared to individual optimized single-junction solar cells. [•] Excellent agreement between experimental data and optical simulations based on a transfer-matrix approach. [•] Optical simulation allows performance prediction of tandem device without time-consuming experimental device optimization. [ABSTRACT FROM AUTHOR]

Abstract: This review provides a summary of the most important developments in the field of solar cells based on the sensitization of p-type semiconductors, such as NiO, and identifies the future challenges and opportunities to enhance their overall performance. In particular, the main factors responsible for the low open-circuit voltage, short circuit photocurrent and fill factor are discussed in detail. [Copyright &y& Elsevier]

Thin-film cadmium telluride (CdTe) solar cells have found widespread application, with current commercially available module efficiencies reaching 14.4% and production costs falling as low as $$ \hbox{US}\,\$0.75/W_{\rm p}$$. Despite the proliferation of this technology, there have been comparatively few developments in research circles in recent years. Rather than attempt to further advance the materials science of CdTe solar cells, it is proposed to realize an efficiency improvement over conventional cells by means of a novel tandem structure. Three such structures are examined herein, and results of simulation using Synopsys Sentaurus TCAD are presented. [ABSTRACT FROM AUTHOR]

Abstract: Recently, Applied Materials has demonstrated the ability to manufacture large area a-Si/μc-Si thin film modules with total area efficiencies of 10% and above. Reducing the production costs is now the key objective for an economic success of this technology. Decreasing the absorber layer thickness or increasing the deposition rate can reduce the cost significantly because the PECVD deposition of the silicon layers is one of the main cost contributors. But this would also reduce the conversion efficiency of amorphous/microcrystalline tandem cells (a-Si/μc-Si TJ cells). Therefore, optimizing TJ cells for maximal productivity requires a careful balancing of layer thicknesses and deposition rates. In this paper we studied the impact of deposition rates and absorber layer thicknesses for top and bottom cells. The reduction of the bottom cell (BC) thickness from 2μm to less than 1μm showed only a small impact on the stabilized module efficiency while having a big impact on the productivity of a production line. The influence of the top cell (TC) deposition rate on the other hand results in a big decrease of the efficiency while having only a small impact on the line output. 10.2% stable mini-module efficiency could be achieved with 900nm BC thickness, reducing the deposition time by 50%. [Copyright &y& Elsevier]

Abstract: Quantum dot materials, in which Si QDs are embedded in a dielectric matrix, offer the potential to tune the effective band gap, through quantum confinement, and allow fabrication of optimised tandem solar cell devices in one growth run in a thin film process. Such cells can be fabricated by sputtering of thin layers of silicon rich oxide sandwiched between a stoichiometric oxide that on annealing crystallise to form Si QDs of uniform and controllable size. For approx. 2nm diameter QDs these result in an effective band gap of 1.8eV. Introduction of phosphorous or boron during the growth of the multilayers results in doping and a rectifying junction, which demonstrates photovoltaic behaviour with an open-circuit voltage of almost 500mV. However, the doping behaviour of P and B in these QD materials is not well understood. In addition P and B have large but opposite effects on QD crystallisation, with P (B) doped material forming larger (smaller) QDs than for undoped material. Alternative materials for quantum dots are Ge and Sn. These allow lower processing temperatures to be used, more compatible with underlying layers. Alternative matrices to SiO2 such as SiNx or SiC offer higher tunnelling probability and hence lower resistance. These alternative matrix materials can also be used as hetero interlayers to improve the transport in the growth direction whilst maintaining quantum confinement. Group IV alloys can also be used to modify band gap. GeC in particular looks to have useful band gap and sputtering properties. Such alloy materials could be used in hetero-junction or homojunction devices in combination with SiQD based materials to fabricate all thin film tandem cells. [Copyright &y& Elsevier]

Small molecule based organic photovoltaic cells have attracted considerable interest as a potential solution for low-cost solar energy conversion in the near future. In this review, we first discuss the operation, advantages, and limitations of three different molecular donor-acceptor heterojunction structures. We then discuss the phase separation in molecule donor-acceptor mixtures and its impact on the photovoltaic performance. Methods to achieve bulk heterojunctions with controlled nanoscale geometry are also reviewed. Finally, we provide an outlook on major remaining challenges to the further development of this photovoltaic technology. [ABSTRACT FROM AUTHOR]

Abstract: To optimize dual junction solar cells using a dye-sensitized cell (DSC) as top cell and a Cu(In,Ga)Se2 (CIGS) cell as bottom cell, both optical and electronic loss mechanisms were investigated. The light absorption and optical losses in various layers were investigated through transmission measurements, and the amount of light available for photogeneration of charge carriers was determined. From the measured light balance, a maximum possible current for the cells was estimated. I-V curves of stacked solar cells were analyzed to investigate possible electronic loss mechanisms. From the results gained in these measurements, conclusions about the limiting factors and potential optimizations in DSC/CIGS tandem solar cells could be drawn. Calculations showed that current densities up to 20 mAcm−2 can be generated in a CIGS bottom cell with the light transmitted from the DSC. This would correspond to an efficiency exceeding 20%, given that highly transmitting DSCs yielding such high currents can be provided. [ABSTRACT FROM AUTHOR]

Abstract: In this study recent results of Micromorph thin film silicon tandem cells with n-doped silicon oxide based intermediate reflectors deposited in the KAI-M industrial PECVD reactor are discussed. From the optical analysis of the devices, specific features in the reflection spectrum attributed to the incorporated intermediate reflector can be observed. In particular, the influence of the Transparent Conductive Oxide (TCO) layer roughness on the reflection spectrum of the cells is studied. Compared to commercial SnO2, reflection losses are reduced and photocurrents are increased by using rougher front TCO-layers like LPCVD-ZnO which should lead to potentially higher efficiencies at same silicon absorber thicknesses. Micromorph tandem cells with intermediate reflector on ZnO leads to 10.18% efficiency after 1000 h of light-soaking, whereas 10.35% have been achieved on commercial SnO2. [ABSTRACT FROM AUTHOR]

Abstract: We optimized tandem-structured dye-sensitized solar cells (T-DSSCs) that consist of a N719-sensitized UV–visible-responsive top cell and a black dye-sensitized near-infrared-responsive bottom cell. The relationship between the thickness (d T) of TiO2 film in the top cell and the performance of T-DSSC was examined both for parallel and series T-DSSCs. The optimized parallel T-DSSC gave the photovoltaic conversion efficiency (η) of 10.6% (aperture area; 0.188cm2, and total area; 0.25cm2) under solar-simulating light conditions (AM 1.5, 100mWcm−2); this η value was certified as the highest value of the conversion efficiency for T-DSSCs. [Copyright &y& Elsevier]

Abstract: CuIn1− x Ga x Se2 (CIGS) solar cells show a good spectral response in a wide range of the solar spectrum and the bandgap of CIGS can be adjusted from 1.0 eV to 1.7 eV by increasing the gallium-to-indium ratio of the absorber. While the bandgaps of Ga-rich CIGS or CGS devices make them suitable for top or intermediate cells, the In rich CIGS or CIS devices are well suited to be used as bottom cells in tandem solar cells. The photocurrent can be adapted to the desired value for current matching in tandem cells by changing the composition of CIGS which influences the absorption characteristics. Therefore, CIGS layers with different [Ga]/[In+Ga] ratios were grown on Mo and ZnO:Al coated glass substrates. The grain size, composition of the layers, and morphology strongly depend on the Ga content. Layers with Ga rich composition exhibit smaller grain size and poor photovoltaic performance. The current densities of CIGS solar cells on ZnO:Al/glass varied from 29 mA cm−2 to 13 mA cm−2 depending on the Ga content, and 13.5% efficient cells were achieved using a low temperature process (450 °C). However, Ga-rich solar cells exhibit lower transmission than dye sensitized solar cells (DSC). Prospects of tandem solar cells combining a DSC with CIGS are presented. [Copyright &y& Elsevier]

Abstract: Multilayer tandem polymer solar cells were prepared by solution processing using thermocleavable polymer materials that allow for conversion to an insoluble state through a short thermal treatment. The problems associated with solubility during application of subsequent layers in the stack were efficiently solved. Devices comprised a transparent front cathode based on solution processed zinc oxide nanoparticles, a large band gap active layer based on a bulk heterojunction between zinc oxide and poly(3-carboxydithiophene) (P3CT) followed by a layer of PEDOT:PSS processed from water. The second cell in the stack employed a zinc oxide front cathode processed on top of the PEDOT:PSS layer from an organic solvent, a low band gap active layer based on a bulk heterojunction between zinc oxide and the novel poly(carboxyterthiophene-co-diphenylthienopyrazine) (P3CTTP) followed by a layer of PEDOT:PSS again processed from water and finally a printed silver electrode. The devices were prepared without the use of fullerenes and vacuum steps and employ only thermal treatments and orthogonal solvents. The devices exhibited operational stability in air without any form of encapsulation. [Copyright &y& Elsevier]

Abstract: For amorphous and ‘micromorph’ silicon multi-junction solar cells, we have developed tunnel recombination junctions consisting of two microcrystalline doped layers with a defect-rich interface. While the solar cells performed reasonably well under AM 1.5 light, we found in spectral response measurements that the first deposited cell of tandem structures in nip and pin configuration was apparently leaking under low light conditions. Insertion of a thin protection layer of n-type amorphous silicon solved this issue, and led to an increase in open-circuit voltage. Voltages as high as 1.76V have been obtained for a-Si/a-Si pinpin tandem cells. [Copyright &y& Elsevier]