Interfacial studies and band alignment engineering on the electron transport layer (ETL) play a key role for fabrication of high‐performance perovskite solar cells (PSCs). Here, an amorphous layer of SnO2 (a‐SnO2) between the TiO2 ETL and the perovskite absorber is inserted and the charge transport properties of the device are studied. The double‐layer structure of TiO2 compact layer (c‐TiO2) and a‐SnO2 ETL leads to modification of interface energetics, resulting in improved charge collection and decreased carrier recombination in PSCs. The optimized device based on a‐SnO2/c‐TiO2 ETL shows a maximum power conversion efficiency (PCE) of 21.4% as compared to 19.33% for c‐TiO2 based device. Moreover, the modified device demonstrates a maximum open‐circuit voltage (Voc) of 1.223 V with 387 mV loss in potential, which is among the highest reported value for PSCs with negligible hysteresis. The stability results show that the device on c‐TiO2/a‐SnO2 retains about 91% of its initial PCE value after 500 h light illumination, which is higher than pure c‐TiO2 (67%) based devices. Interestingly, using a‐SnO2/c‐TiO2 ETL the PCE loss was only 10% of initial value under continuous UV light illumination after 30 h, which is higher than that of c‐TiO2 based device (28% PCE loss).

power conversion effi ciency (PCE) more than 20% has been achieved using a solution process. [6][7][8][9][10] Among the different processes for fabrication of perovskite solar cells, including one-step solution process, [ 11,12 ] sequential deposition, [ 13,14 ] vacuum deposition, [ 15 ] and chemical vapor deposition, [ 16 ] a two-step solution process has benefi ts such as good control of the crystal structure for perovskite fi lm. [ 17 ] In order to fabricate perovskite solar cells, different types of electron transfer layers (ETLs) and hole transfer layers (HTLs) have been employed. Among them, a conducting polymer such as poly(3,4-ethylenedioxythiophene):polystyr enesulfonate (PEDOT:PSS) is commonly used as the HTL in perovskite solar cells. However, the high acidity of this polymer deteriorates the ITO layer, and its high hygroscopicity can also accelerate degradation of the device due to water absorption. [ 18 ] Recently, many research groups have focused on inorganic materials that can work as an HTL, such as CuSCN and NiO. [19][20][21] Regarding the ETL materials, more stable metal oxides, such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), and tin oxide (SnO 2 ) have been developed for perovskite solar cells. [ 22 ] Among these metal oxides, TiO 2 -nanoparticles (NPs) have been commonly used as the ETL to provide an effi cient charge collection. [ 23 ] In order to prepare a TiO 2 mesoporous layer, a sintering process with high temperature (≈500 °C) is required. [ 18 ] This temperature is too high for fabrication of perovskite on plastic substrate. In addition, few groups already have reported ETL-free perovskite solar cell with descent PCE on plastic substrates; however, their PCE is not comparable with those devices fabricated on rigid substrates.ZnO NPs are, therefore, a promising candidate to replace TiO 2 NPs as the ETL layer in perovskite solar cells. However, only a few works have reported perovskite solar cells based on ZnO NPs. Intriguingly, the devices on ZnO NPs show a maximum PCE of close to 15.7%, [ 24 ] which is lower than those on TiO 2 NPs. To fabricate the device on ZnO NPs, a twostep solution process is usually employed. Depending on the annealing temperature (70 °C-100 °C) of the perovskite fi lm, different works have reported a device performance from 8.9% to 15.7%. [24][25][26][27] In addition, a few works have demonstrated the instability of perovskite materials on top of ZnO NPs due to Fabrication of organohalide perovskite materials on the top of ZnO nanoparticles (NPs) has some benefi cial advantages such as room temperature processing; however, the perovskite is not stable on ZnO NPs layer during the annealing process. In fact, there are only a few reports about the fabrication of perovskite solar cells on ZnO NPs layer. Herein, the decomposition mechanism of CH 3 NH 3 PbI 3 perovskite materials on ZnO is reported, and it is found that the perovskite fi lm on the top of the ZnO layer is converted into PbI 2 during the annealing process due to the existence of hydroxide groups on...

Interface engineering in organometal halide perovskite solar cells (PSCs) has been an efficient tool to boost the performance and stability of photovoltaic (PV) devices.

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Interface engineering of solar cell device is a prominent strategy to improve the device performance. Herein, we synthesize reduced-graphene scaffold (rGS) by using a new and simple chemical approach. In this regard, we synthesize a hollow structure of graphene and then fabricate a three-dimensional scaffold of graphene with a superior surface area using electrophoretic process. We employ this scaffold as an interface layer between the electron transfer and absorber layers in perovskite solar cell. The characterization tests and photovoltaic results show that rGS improves the carrier transportation, yielding a 27% improvement in device performance as compared to conventional device. Finally, a power conversion efficiency of 17.2% is achieved for the device based on the graphene scaffold. Besides, rGS amends the stability and hysteresis effect of the perovskite solar cell.

In this work, a novel and facile synthesis process to fabricate single crystalline organometal halide perovskite nanowires has been successfully developed. Nanowires were grown in a high density ordered array from metal nanoclusters inside anodic aluminum oxide templates using a non-catalytic chemical vapor deposition method. Specifically, perovskite NWs were grown as a result of the reaction between methylammonium iodide (MAI) and the Pb/Sn (Pb or Sn) metal in anodic aluminum oxide templates under optimal conditions. The characterization results show that there is a reaction zone at the interface between the perovskite material and metal, at the bottom of the anodic aluminum oxide nanochannels. In order to sustain perovskite NW growth, MAI molecules have to diffuse downward through the perovskite NWs to reach the reaction zone. In fact, the reaction is facilitated by the formation of an intermediate product of the metal iodide compound. This suggests that the Pb/Sn metal is converted to PbI/SnI first and then perovskite NWs are formed as a result of the reaction between MAI and PbI/SnI through a vapor-solid-solid process. The optical characterization results demonstrate that the as-synthesized NWs with an ultra-high nanostructure density can serve as ideal candidates for optoelectronic devices, such as solar cells, light-emitting didoes, photodetectors, etc. And the reported growth approach here is highly versatile combining the merits of excellent controllability, cost-effectiveness and tunability on material composition and physical properties.

Down-shifting QDs together with moisture-assisted film growth enable a highly efficient and stable inverted perovskite solar cell with efficiency of over 20%.