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Perovskite solar cells (PSCs) have exhibited tremendous potential in photovoltaic fields owing to their appreciable performance and simple fabrication. Nevertheless, device performances are still required to be further improved before commercial applications. As one‐dimensional materials, carbon nanotubes (CNTs) have been utilized to regulate stability and efficiency of PSCs because of their excellent chemical stability, flexibility, as well as tunable optical and electrical characteristics. In this review, we comprehensively summarize various functions of CNTs in PSCs, such as transparent electrodes, hole/electron‐transport layers, counter electrodes, perovskite additives, and interlayers. Additionally, applications of CNTs toward the advancement of flexible and semitransparent PSCs are provided. Finally, we preview the challenges and research interests of using CNTs in high‐efficiency and stable perovskite devices. [ABSTRACT FROM AUTHOR]

Rationally managing the secondary‐phase excess lead iodide (PbI2) in hybrid perovskite is of significance for pursuing high performance perovskite solar cells (PSCs), while the challenge remains on its conversion to a homogeneous layer that is robust stable against environmental stimuli. We herein demonstrate an effective strategy of surface reconstruction that converts the excess PbI2 into a gradient lead sulfate‐silica bi‐layer, which substantially stabilizes the perovskite film and reduces interfacial charge transfer barrier in the PSCs device. The perovskite films with such bi‐layer could bear harsh conditions such as soaking in water, light illumination at 70 % relative humidity, and the damp‐thermal (85 °C and 30 % humidity) environment. The resulted PSCs deliver a champion efficiency up to 24.09 %, as well as remarkable environmental stability, e.g. retaining 78 % of their initial efficiency after 5500 h of shelf storage, and 82 % after 1000 h of operational stability testing. [ABSTRACT FROM AUTHOR]

The ionic nature endows halide perovskites with intrinsic interfacial defects in the formed polycrystalline films, thus imposing the challenge of synchronously passivating these defects with low formation energies that directly account for the unsatisfied performance of perovskite solar cells (PSCs). By virtue of the theoretically proven capability of a three to four times enhancement of the formation energy of each defect of Pb‐I antisite (PbI) and iodine vacancy (VI), a new passivation molecule of 1,10‐phenanthrolin‐5‐amine (PAA) is intentionally explored to synchronously passivate the dual defects. The pronounced passivation effect is experimentally verified by the sharp enhancement of the open‐circuit voltage in ternary PSCs from the original 1.118 up to 1.207 V, as well as the construction of PAA‐modified formamidinium lead iodide PSCs with a champion efficiency up to 24.06%, thus providing a universal alternative of addressing interfacial charge carrier dynamics and operational stability of PSCs that are bothered by the multiple interfacial defects. [ABSTRACT FROM AUTHOR]

CsPbI2Br perovskite solar cells have achieved rapid development owing to their exceptional optoelectronic properties and relatively outstanding stability. However, open‐circuit voltage (Voc) loss caused by band mismatch and charge recombination between perovskite and charge transporting layer is one of the crucial obstacles to further improve the device performance. Here, we proposed a bilayer electron transport layer ZnO(bottom)/SnO2(top) to reduce the Voc loss (Eloss) and promote device Voc by ZnO insert layer thickness modulation, which could improve the efficiency of charge carrier extraction/transfer and suppress the charge carrier recombination. In addition, guanidinium iodide top surface treatment is used to further reduce the trap density, stabilize the perovskite film and align the energy levels, which promotes the fill factor, short‐circuit current density (Jsc), and stability of the device. As a result, the champion cell of double‐side optimized CsPbI2Br perovskite solar cells exhibits an extraordinary efficiency of 16.25% with the best Voc as high as 1.27 V and excellent thermal and storage stability. [ABSTRACT FROM AUTHOR]

With the power conversion efficiency (PCE) surpassing 25%, the eye‐catching and promising perovskite materials have proved to be potential competitors in photovoltaic field. Till now, massive efforts have been invested into this blooming flower to further raise its efficiency approaching the Shockley‐Queisser limit (SQ limit) and improve its stability for prolonging effective operation life. In details, various methods including component engineering, structure optimization and interfacial treatment have been used for realizing efficient and stable devices. Especially, the charge transport layers usually play critical roles in effective extraction and transportation of charge carriers. Compared with organic charge transport materials, inorganic materials generally demonstrate excellent stability due to their superior film qualities and inert chemical properties. Moreover, low cost, high charge mobility and material stability have been proved for inorganic electron and hole transport materials. This review summarizes the general progress of different inorganic hole transport materials in perovskite solar cells of recent years for better acquaintance of their contribution in efficient and stable devices. The discussions about performance improvement in the future directions are also provided. [ABSTRACT FROM AUTHOR]

Understanding the crystal anisotropy effect of materials on optical and electrical properties is crucial for further comprehension of the device operating mechanism and device performance improvement. In this study, a detailed theoretical analysis is performed to explore the crystal anisotropy effect on the performance of perovskite solar cells by employing state‐of‐the‐art multiscale simulations connecting from the material (first‐principle theory) to the device (drift‐diffusion model). According to the results obtained from first‐principle calculation, the mobility and absorption coefficient of CsPbIBr2 and CsPbI2Br along the [001] orientation are larger than those along the [100] orientation, suggesting that the transport properties and optical properties along the [001] orientation are superior to those along the [100] orientation. According to the results obtained from the drift‐diffusion model, owing to the superior optical and transport characters along the [001] direction, the optimal power conversion efficiencies (PCEs) of CsPbI2Br (18.88%) and CsPbIBr2 (16.42%) solar cells can be obtained. In addition, the two‐terminal CsPbIxBr3‐x/silicon tandem solar cell is also investigated. By utilizing CsPbIBr2/silicon and CsPbI2Br/silicon tandem structures along the [001] orientation, ultrahigh efficiencies are achieved up to 26.32% and 31.39%, respectively. Therefore, the [001] crystal orientation of CsPbIBr2 and CsPbI2Br is more suitable for further applications of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Recent research shows that the interface state in perovskite solar cells is the main factor which affects the stability and performance of the device, and interface engineering including strain engineering is an effective method to solve this issue. In this work, a CsBr buffer layer is inserted between NiOx hole transport layer and perovskite layer to relieve the lattice mismatch induced interface stress and induce more ordered crystal growth. The experimental and theoretical results show that the addition of the CsBr buffer layer optimizes the interface between the perovskite absorber layer and the NiOx hole transport layer, reduces interface defects and traps, and enhances the hole extraction/transfer. The experimental results show that the power conversion efficiency of optimal device reaches up to 19.7% which is significantly higher than the efficiency of the device without the CsBr buffer layer. Meanwhile, the device stability is also improved. This work provides a deep understanding of the NiOx/perovskite interface and provides a new strategy for interface optimization. [ABSTRACT FROM AUTHOR]

Abstract: NiOx hole transporting layer has been extensively studied in optoelectronic devices. In this paper, the low temperature, solution–combustion‐based method is employed to prepare the NiOx hole transporting layer. The resulting NiOx thin films show better quality and preferable energy alignment with perovskite thin film compared to high temperature sol–gel‐processed NiOx. With this, high‐performance perovskite solar cells are fabricated successfully with power conversion efficiency exceeding 20% using a modified two‐step prepared MA1−yFAyPbI3−xClx perovskite. This efficiency value is among the highest values for NiOx‐based devices. Various characterizations and analyses provide evidence of better film quality, enhanced charge transport and extraction, and suppressed charge recombination. Meanwhile, the device exhibits much better device stability compared to sol–gel‐processed NiOx and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)‐based devices. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have attracted much attention due to their high power conversion efficiency (PCE) and low cost fabrication. Since the PCE is critically related to the perovskite crystal morphology and quality, controlling the perovskite crystal formation is becoming more important. In this work, we chose PDDA polyelectrolyte as the crystal capping agent to modulate the perovskite thin film formation. The PDDA capping agent significantly enhanced the short-circuit current ( J sc ) and fill factor (FF) of the corresponding PSCs, which produced an optimal PCE of 14.1% compared to 12.5% of control device without the modifying agent. The effect of PDDA agent is examined by various techniques. It was found that improved surface morphology, enhanced crystallinity, and decreased grain boundary related defects are contributed to the performance and stability enhancement. [ABSTRACT FROM AUTHOR]

Planar perovskite solar cells (PSCs) with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have attracted much interest because they can be fabricated by low temperature process and exhibit high power conversion efficiency (PCE). The PCE is strongly dependent on the interface properties between the PCBM layer and cathode. In this work, solution-processable material, rhodamine 101, was used as the interfacial layer between the PCBM layer and Ag cathode. These interfacial materials significantly increase the fill factor so as to the PCE of the PSCs. The optimal power conversion efficiencies are 13.2% (CH 3 NH 3 PbI 3 ) and 14.8% (CH 3 NH 3 PbI 3−x Cl x ) for the devices with rhodamine 101 as the electron collection interlayer, saliently higher than that (8.5% and 12.0%) of control devices without an electron-collection interlayer. The effect of the interfacial material is carefully examined by time-resolved photoluminance spectroscopy (TR-PL), ultraviolet photoelectron spectroscopy (UPS), and kelvin probe force microscopy (KPFM) techniques. Decreased work-function and energy barrier, enhanced electron extraction and prolonged free carrier lifetime all contributed to the photovoltaic performance improvement. [ABSTRACT FROM AUTHOR]

The charge transport layer is crucial to the performance and stability of the perovskite solar cells (PSCs). Compared with other conventional metal oxide electron transport materials, SnO2 has a deeper conduction band and higher electron mobility, and can efficiently serve as an electron transport layer to facilitate charge extraction and transfer. Herein, an optimized low‐temperature solution‐processed SnO2 electron transport layer is achieved by doping polyethylenimine polyelectrolyte into SnO2 for the first time in the PSCs. It is found that the performance of all aspects of the doped SnO2 film is improved over that of the pristine SnO2 film. The better energy level alignment, larger built‐in field, enhanced electron transfer/extraction, and reduced charge recombination all contribute to the improved device performance. Finally, a PSC with a power conversion efficiency of 20.61% is successfully prepared under low temperature below 150 °C. Moreover, the stability of the doped SnO2‐based device is also greatly improved. [ABSTRACT FROM AUTHOR]

Material passivation is essential to enhance the quality of perovskite materials and boost the performance of perovskite solar cells (PSCs). However, most of the previous reports only paid attention to improving the quality of perovskite films by adopting single passivation. Here, a facile strategy that can carry out double passivation to improve the performance of PSCs is demonstrated. By using the dilute halide salt PEABr solution to treat the perovskite film, PbI2 can precipitate from the perovskite. Both PEABr and PbI2 can passivate the perovskite film, and by combining PEABr and PbI2, the double passivation improves the performance of PSCs significantly. Very high short‐circuit current density of 24.30 mA cm−2, open‐circuit voltage of 1.10 V, and fill factor of 79.75% are achieved which lead to a surprising efficiency of 21.32% for the passivated device. The improved efficiency is mainly according to the available surface passivation of the perovskite material, leading to repressed nonradiative recombination and unhindered charge collection. In addition, the passivated device exhibits better power conversion efficiency stability relative to the control device. [ABSTRACT FROM AUTHOR]

2D/3D perovskite heterostructures or composites are recognized as efficient strategies to improve the stability of perovskite solar cells. Herein, a novel solution process to develop 2D/3D perovskites with modulated diffusion passivation by introducing phenylethylammonium iodide (PEAI) and N,N‐dimethylformamide (DMF) additive, which could effectively enhance device performance and long‐term stability, is demonstrated. Compared with conventional devices, the device with PEAI and DMF solvent additive treatment exhibit enhanced charge transport, improved charge extraction, and suppressed nonradiative carrier recombination. The solar cells with an optimal 2D/3D perovskite passivation treatment exhibit an extremely high fill factor of 83.6% and an average power conversion efficiency of 21.4% (21.3% using integrated photocurrent from the incident photon‐to‐current efficiency spectra) based on the NiOx hole transport layer. Furthermore, the unencapsulated device exhibits excellent stability under continuously simulated sunlight illumination and outstanding air stability after 1000 h of storage under ambient air conditions. [ABSTRACT FROM AUTHOR]

ZnO is considered as a potential electron transport layer (ETL) in solar cells due to its high charge carrier mobility and low‐temperature processability. However, it is challenging to obtain highly efficient and stable perovskite solar cells (PSCs) using low‐temperature ZnO ETL due to the poor chemical compatibility between ZnO and perovskite films. Hence, proper surface passivation strategies of ZnO ETL are developed to enhance the ZnO/perovskite interface stability for highly efficient PSCs. In this study, low‐temperature TiOx post‐treatment is performed to passivate the ZnO surface, suppress the interface charge recombination, and stabilize the ZnO/perovskite interface. The fullerene treatment is further applied to enhance the electron transfer from perovskite to ZnO and reduce the hysteresis behavior. Finally, high‐performance PSCs with an efficiency of over 20% and improved stability are achieved. [ABSTRACT FROM AUTHOR]

We present that atomic layer deposition (ALD) of TiO 2 thin layer on SnO 2 electron transport layer (ETL) could simultaneously boost the crystallization control of CsPbIBr 2 absorber film and band alignment of all-inorganic perovskite solar cell (PSC). The former awards the desired CsPbIBr 2 film characterized by high crystallinity, weak halide phase separation, as well as extremely uniform- and large-sized grains. And, the latter brings a cascade pathway for electron extraction and transport in the cell. Such combined morphology tailoring and interface engineering are extremely beneficial to suppress both bulk recombination and interfacial recombination of charge carrier. As a result, the cell' efficiency can be boosted from 6.11% to 9.31%, which is beyond all the pure CsPbIBr 2 -based PSCs reported to date. Therefore, our works highlight the dual functions of ALD-processed TiO 2 interfacial layer in processing high-performance all-inorganic PSC. Atomic layer deposition (ALD) of TiO 2 thin layer on SnO 2 electron transport layer could simultaneously boost the crystallization control of CsPbIBr 2 absorber film and band alignment of all-inorganic perovskite solar cell. Thus, the cell efficiency can be boosted from 6.11% to the record-high value of 9.31%. Image 1 • ALD-processed TiO 2 on SnO 2 ETL triggers dual functions of crystallization control and band alignment in CsPbIBr 2 PSC. • Crystallization control enables high crystallinity, weak phase separation, and uniformly large-sized grains in CsPbIBr 2 film. • Band alignment facilitates a cascade pathway for electron extraction and transport. • The dual functions of TiO 2 thin layer boost efficiency of pure CsPbIBr 2 -based cell to the record-high value of 9.31%. [ABSTRACT FROM AUTHOR]

Interface engineering is of critical importance to achieve high performance perovskite solar cells. Herein, a readily-prepared and sustainable hole transport layer (HTL) based on the poly(3,4-ethylenedioxy-thiophene):sulfonated acetone-formaldehyde (PEDEO:SAF) as an alternative of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is reported to efficiently improve the film electrical properties, enhance the charge transfer and extraction, and finally enhance the efficiency and stability of inverted perovskite solar cells. Compared with PEDOT:PSS HTL, PEDOT:SAF HTL possesses higher film conductivity, and less acidity, leading to much improved ambient stability of devices. This work suggests that PEDOT:SAF HTL could be an efficient HTL for high performance and stable perovskite solar cells. Image 1 • The perovskite solar cell efficiency was enhanced by using PEDOT:SAF hole transport layer. • Higher film conductivity and less acidity were contributed to the performance and stability improvement. • The charge transfer and extraction process was enhanced by using PEDOT:SAF hole transport layer. [ABSTRACT FROM AUTHOR]

• TiO 2 electron transport layer deposited by ALD at about 150 °C. • SnO 2 /PCBM double modifier at TiO 2 /perovskite interface. • Low-temperature processed perovskite solar cells with a PCE of 19.45%. • Enhanced performance compared to devices with solution processed TiO 2. Perovskite solar cells (PSCs) have attracted increasing attentions for their outstanding efficiency and simple fabrication process. However, the commonly used typical titanium dioxide (TiO 2) electron transport layer (ETL) requires a high-temperature treatment to crystallize. In this work, the low-temperature (150 °C) atomic layer deposition (ALD) processed TiO 2 ETL, and the SnO 2 /PCBM double interfacial modifier have been adopted to fabricate the high performance PSCs of ITO/ALD-TiO 2 /SnO 2 /PC 61 BM/MA 0.7 FA 0.3 PbI (3-x) Cl (x) /Spiro-OMeTAD/Ag. The measurement results show that the PSCs with ALD-TiO 2 ETL obtain the higher champion PCE of 19.45% than that of PSC with solution-TiO 2 ETLs (PCE = 18.64%), along with the obviously enhanced FF and V OC , as well as the better light stability and repeatability. And the transient photocurrent and photovoltage results demonstrate that the performance improvement origins from the enhanced charge transport and suppressed charge recombination. Therefore, the low-temperature ALD-TiO 2 ETL with suitable modification is a promising strategy to fabricate efficient PSCs and flexible devices. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate a facile way to improve the quality of perovskite film by a regrowth process via using the mixed solution to post-treat the perovskite material after the film formation. By using the regrowth method, XRD measurement shows that the crystal quality of the perovskite film is improved, SEM results demonstrate that the perovskite material shows a relatively uniform grain size and the electrical impedance spectroscopy measurement shows that the recombination is lowered. The photoluminescence spectra measurement also shows that the optimal perovskite film has a longer carrier lifetime compared to the control film. The transient photocurrent/photovoltage measurements confirm that the devices after the regrowth not only have outstanding ability of charge extraction but also greatly suppress the charge recombination. The corresponding efficiency of perovskite solar cells with construction of ITO/NiO x /MA 0.7 FA 0.3 PbI 3-x Cl x /PCBM/BCP/Ag is improved from 16.33% to 18.21% owing to the optimal perovskite film. All the results show that the regrowth method with the mixed solution post-treatment is a facile way to boost the film quality and the device performance. A facile way is demonstrated to improve the quality of perovskite film by a regrowth process via using the mixed solution to post-treat the perovskite material after the film formation. Image 1 • A facile regrowth way assisted by the mixed solution to improve the perovskite quality. • Improved material quality and enlarged grain size. • Enhanced charge extraction and suppressed charge recombination. • Improved power conversion efficiency of the perovskite solar cells. [ABSTRACT FROM AUTHOR]

Abstract The performance of planar perovskite solar cells (PSCs) is very sensitive to the interfaces properties, especially the electron transport layer (ETL)/perovskite interface in the n-i-p structure, which could significantly influence the perovskite film morphology, crystallinity and the charge extraction and collection efficiency. Therefore, interface engineering is crucial for achieving high performance planar PSCs. Here, we reported a simple and effective interface engineering method which employed phenyl-C61-butyric acid methyl ester (PC 61 BM) thin film or fullerene (C 60) self-assembled monolayer (SAM) or their combination to modify the titanium dioxide (TiO 2)/perovskite interface to obtain high performance PSCs. A comparative study between the effects of different fullerene derivative modifications was taken and indicated that adding proper C 60 -SAM into the PC 61 BM solution could improve the interface contact, increase the charge extraction and collection efficiency more obviously compared to the pristine PC 61 BM treatment. By combining the modified two-step spin coating method, the best performance device based on C 60 -SAM modified TiO 2 achieved a power conversion efficiency (PCE) of 17.8%, much higher than the control device without the interface treatment (12.9%) and also higher than the PC 61 BM modified device (16.1%) based on MA 1-y FA y PbI 3-x Cl x perovskite. As a consequence, such interface engineering via C 60 -SAM or PC 61 BM + C 60 -SAM combination modification is a promising method for achieving highly efficient PSCs. Graphical abstract Image 1 Highlights • Interface engineering of perovskite/TiO 2 interface with fullerene derivatives was conducted. • The charge transfer increased and the charge recombination was reduced after interface treatment. • The fullerene treatment passivated the TiO 2 surface defects, resulting in the performance and stability improvement. [ABSTRACT FROM AUTHOR]

The perovskite solar cells have attracted great attention owing to their low cost and high performance. For perovskite solar cells, metal oxides demonstrated great potential with much higher charge carrier mobility and superior stability than organic materials. In this study, we employed NiO as hole transport layer and chloride-doped CH 3 NH 3 PbI 3 (CH 3 NH 3 PbI 3−x Cl x ) as absorber due to its enhanced performance. We investigated the effects of several parameters on the solar cell performance through device simulation. It was found that solar cell performance was related to the doping concentrations of NiO and PCBM, and the thicknesses of perovskite and NiO interlayer. The optimized performance of perovskite solar cells with power conversion efficiency (PCE) of 22.0% was achieved when doping concentrations of NiO and PCBM were 1 × 10 17  cm −3 and 1 × 10 19  cm −3 , respectively, and thicknesses of perovskite and NiO were 450 nm and 30 nm, respectively. Moreover, a high PCE of 18.0% was obtained based on experimental condition. These results showed that this kind of solar cell was a potential choice for perovskite solar cells with high efficiency. [ABSTRACT FROM AUTHOR]

Bifacial semi-transparent perovskite solar cells (PSCs) are highly attractive for improving the efficiency of tandem solar cells and extending bifacial photovoltaic applications. However, the further improvement of bifacial performance has always been limited by the semitransparent electrode. Here we report an efficient triple-layer cathode of polyethyleneimine ethoxylate/silver/molybdenum oxide (PEIE/Ag/MoO x ) for hysteresis-free planar PSCs with an inverted device configuration. Firstly, the optimal thickness of Ag electrode (11 nm) is achieved by theoretical calculation, and the fabricated PSC achieves the PCE of 8.04% at indium-tin-oxide (ITO) side and 5.24% at Ag film side. Then, by introducing the MoO x (10 nm) optical coupling layer and PEIE (10 nm) interfacial modifying layer, the resulted PSC shows an obviously increased PCEs of 13.55% (ITO side) and 8.41% (Ag side), which is 60% higher than that of Ag only PSCs. The optimized PSCs has a structure of Glass/ITO/Poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate)/Methylammonium-Lead-Iodide (about 300 nm)/Phenyl-C 61 -butyric-acid-methyl-ester/PEIE/Ag/MoO x . It is thought that the enhanced Ag film transmittance by high-refractive-index MoO x and electron extraction ability by low-work-function PEIE contribute to the improved cathode property and bifacial PSC performance. Moreover, when a back-reflector is employed, the PCE of device could be further improved to 14.50% (ITO side) and 11.37% (Ag side). [ABSTRACT FROM AUTHOR]

In this work, we demonstrated a high performance planar heterojunction perovskite solar cell with the polyethylenimine ethoxylated (PEIE) interlayer. By adopting a less polar solvent for PEIE, enhanced device performance and uniformity are achieved. The power conversion efficiency (PCE) of the best device increases by 22% compared to the reference device and reaches 14.82% with J SC of 19.45 mA/cm 2 , V OC of 1.00 V, and FF of 76.31% under AM 1.5G 100 mW/cm 2 light illumination. The UPS measurement shows that the PEIE layer can effectively decrease the energy offset between PCBM and metal electrode. The recombination mechanism was explored by measuring V OC and J SC at various light intensities from 100 to 0.1 mW/cm 2 . It shows that the PEIE layer can suppress the trap-assisted recombination for the devices. The enhancement of the probability of the carriers collection also shows that the recombination is reduced by the PEIE interlayer. Moreover, it is found PEIE layer can improve the stability of the device. [ABSTRACT FROM AUTHOR]

Since the power conversion efficiencies of organic-inorganic hybrid perovskite solar cells have a rapid development due to their high light absorption coefficient, tunable band gap and low fabrication cost, they have received much attention. The thin film formation and properties have significant effects on the final device performance. While how to control the thin film evolution and introduce film passivation is a critical issue to improve the device efficiency. In this study, we studied the controlled in-situ PbI 2 formation during the thin film evolution, and its effect on thin film properties, as well as their passivation effects on the photovoltaic device performance. The final thin film properties are critically related with the precursor used and chlorine inclusion could change the final thin film compositions, and affect the solar cell performance. We further perform a secondary passivation by reacting the excess PbI 2 with large organic cation to form 2D perovskite. Based on in-situ PbI 2 passivation and secondary 2D perovskite passivation, the devices exhibit a higher PCE of 21.1% and excellent V oc of 1.14 V. [Display omitted] • Controlled in-situ PbI2 formation during the film evolution is achieved. • 2D perovksites as secondary surface passivation by reacting the excess PbI2. • A higher PCE of 21.1% and excellent V oc of 1.14 V are achieved via controlled in-situ PbI2 and 2D perovksite passivation. [ABSTRACT FROM AUTHOR]

• An effective SnO 2 :InCl 3 composite is used as ETL for planar perovskite solar cells. • Cl ions can passivate the defects on the SnO 2 surface and perovskite grain boundaries. • In ions themselves are suitable dopants and can provide better doping performance for SnO 2. • The simultaneous ETL doping and interface passivation result in a significant enhanced PCE and short-circuit current density. There are many defect states at the interface between SnO 2 and perovskite due to the preparation process and the lattice mismatch. These defects will trap photo-generated carriers, resulting in low carrier extraction efficiency and loss of device stability. Many researches are underway to further improve the performance of perovskite solar cells (PSCs) based on SnO 2 electron transport layer (ETL), including doping of ETL and effective passivation of interface defects. Here, the SnO 2 :InCl 3 ETL is used in planar perovskite solar cells to simultaneously dope ETL and passivate the defects at the ETL/perovskite interface. First, Cl ions can passivate the defects on the SnO 2 surface, and part of the chloride ions can also diffuse into the perovskite to passivate the grain boundaries. Additionally, In ions themselves are suitable dopants and can provide better doping performance for SnO 2. The result shows that the simultaneous ETL doping and interface passivation result in a significant increase of PCE from 19.1% to 20.8% due to the enhancement of short-circuit current density. This method expands the ETL/perovskite interface optimization work by using anions and cations for passivation and doping, respectively, and has some inspiration for the delivery of high efficiency and stable planar structure PSCs based on SnO 2 ETL. [ABSTRACT FROM AUTHOR]

Many recent studies have shown that perovskite solar cells (PSCs) employing SnO 2 as an electron transport layer (ETL) exhibit extremely high efficiency which is close to that of the device with the same structure using TiO 2. Considering the sensitivity of the PSC performance to the ETL/perovskite interface, interface engineering of the SnO 2 electron transport layer helps to further release the potential of planar structure PSCs and promote their commercialization. Herein, we introduce an amino acid self-assembled layer onto the SnO 2 ETL as the buffer layer to modulate the SnO 2 /perovskite lattice mismatch induced interface stress, and enhanced the interface interaction between SnO 2 and perovskite caused by hydrogen-bonding and/or electrostatic interactions between the amino groups and the perovskites framework. Due to the improved perovskite film quality and enhanced interface charge transfer/extraction, a champion efficiency of 20.68% (J sc = 24.15 mA/cm2, V oc = 1.10 V, and FF = 0.78) is obtained for Cs 0.05 MA y FA 0.95-y PbI 3-x Cl x planar PSCs. • The amino acid buffer layer as the buffer layer is introduced on SnO 2 ETL. • The interface interaction between SnO 2 and perovskite is enhanced. • The buffer layer enhances the charge transfer and collection at interface. • High efficiency perovskite solar cells over 20% and good stability are achieved. [ABSTRACT FROM AUTHOR]

• Graphene quantum dots (GQDs) are used to modify the SnO 2 ETL in perovskite solar cells. • The GQDs increase the electronic coupling as well as energy levels matching between the perovskite and SnO 2 ETL. • The combination of SnO 2 :GQDs leads to a significant improvement of efficient charge carrier extraction and suppression of the charge recombination. • A high PCE of 21.1% is obtained, which is increased by 13.4% in comparison with the device based on the SnO 2 -only ETL (18.6%). In this work, Graphene quantum dots (GQDs) was decorated on the SnO 2 electron transport layers (ETLs) to boost the performance of perovskite solar cells (PSCs). The power conversion efficiency (PCE) of 21.1% was acquired with the combination of SnO 2 and GQDs. Compared with the SnO 2 -only ETL devices (18.6%), the PCE of SnO 2 /GQDs based devices is greatly enhanced in PCE by the value of 13.4% as well as in the stability. Investigation reveals that with the combination of SnO 2 and GQDs, the open circuit voltage (V OC) and the short circuit current density (J SC) could increase. Various advanced optical and electrical characterizations were carried out to explore the action mechanism of GQDs. The experimental results convinced that the introduction of GQDs leads to the better carrier transportation and extraction by increasing the electronic coupling and matching the energy levels between the perovskite and SnO 2 ETL. Also, the perovskite film quality deposited on the GQDs decorated SnO 2 ETL is better compared with the SnO 2 only. Furthermore, the device stability based on the GQDs modified SnO 2 is evidently improved contrast to the SnO 2 -only device. Its performance kept above 80% of initial value after 720 h storage. [ABSTRACT FROM AUTHOR]

Interface engineering is generally requisite for highly efficient perovskite solar cells (PSCs). However, the current interface engineering methods inevitably introduce extra modifier layers into PSCs, which not only complex the configurations and fabrication procedures, but also increase the production cost of PSCs. Herein, we propose an interface engineering strategy for PSCs by controlling the nature of Lead halide perovskite films, and specifically their interfacial grain facets. In detail, a solution-mediated secondary growth (SSG) technology is demonstrated to tailor interfacial grain facets in CH 3 NH 3 PbI 3 PSC. The precise tailoring ability of interfacial grain facets is achieved by controlling SSG temperature. When it is optimized to 60 °C, interfacial grains of CH 3 NH 3 PbI 3 film can be fully transform from dodecahedral-shaped ones enclosed by (100) and (112) facets to the cubic-shaped ones enclosed by (110) and (002) facets, while maintaining the film's crystalline phase and composition. More importantly, such transitions are accompanied by significantly improved average PCE from 16.51 ± 0.64% to 18.40 ± 0.67% for the optimized CH 3 NH 3 PbI 3 PSCs, benefiting from the greatly suppressed recombination and enhanced extraction of carriers. Transition of interfacial CH 3 NH 3 PbI 3 grain facets from (100)/(112) to (110)/(002) triggers much improved interfacial carrier dynamics and hence cell efficiency. Image 1 • A SSG technology is demonstrated to modulate interfacial grain facets in CH 3 NH 3 PbI 3 PSC. • Interfacial grain facets of CH 3 NH 3 PbI 3 film are transformed from (100)/(112) to (110)/(002). • Tailored interfacial grain facets lead to improved average PCE from 16.51 ± 0.64% to 18.40 ± 0.67%. [ABSTRACT FROM AUTHOR]

Planar halide perovskite solar cells (PSCs) have undergone rapid development in last decade due to their excellent optoelectronic properties. An electron transport layer (ETL) with high electron mobility is crucial to achieve high power conversion efficiency (PCE). TiO 2 is one of the most common ETLs in n-i-p planar PSCs. But the low electron mobility and high annealing temperature of TiO 2 hamper the device performance and applications. In 2 O 3 has a higher electron mobility and wider bandgap compared with TiO 2 ETL. Herein, we report a low-temperature combustion synthesized In 2 O 3 as ETL for PSCs. The electron mobilities of In 2 O 3 films are investigated by the thin film transistors (TFTs) under annealing at different temperatures. By optimizing the In 2 O 3 layer, a power conversion efficiency of 18.12% is obtained, and is among the highest values for PSCs based on In 2 O 3 ETL. Meanwhile, the unencapsulated devices exhibit a remarkable stability, retaining 75% of the initial value after over 120 days' storage. Image 1 • Low temperature combustion synthesized In 2 O 3 was used as electron transport layer. • The In 2 O 3 layer exhibited high electron mobility for thin film transistors. • The In 2 O 3 layer enhanced the charge transfer and collection at interface. • High efficiency perovskite solar cells over 18% and good stability were achieved. [ABSTRACT FROM AUTHOR]