Lead-free tin perovskite solar cells (PSCs) show the most promise to replace the more toxic lead-based perovskite solar cells. However, the efficiency is significantly less than that of lead-based PSCs as a result of low open-circuit voltage. This is due to the tendency of Sn2+ to oxidize into Sn4+ in the presence of air together with the formation of defects and traps caused by the fast crystallization of tin perovskite materials. Here, post-treatment of the tin perovskite layer with edamine Lewis base to suppress the recombination reaction in tin halide PSCs results in efficiencies higher than 10%, which is the highest reported efficiency to date for pure tin halide PSCs. The X-ray photoelectron spectroscopy data suggest that the recombination reaction originates from the nonstoichiometric Sn:I ratio rather than the Sn4+:Sn2+ ratio. The amine group in edamine bonded the undercoordinated tin, passivating the dangling bonds and defects, resulting in suppressed charge carrier recombination.

Perovskite solar cells (PSCs) have attracted extensive research interest in the last decade due to their high power conversion efficiency (PCE) and simple solution-based fabrication process. [1,2] Evolved from dye-sensitized solar cells (DSSCs), [3] typical PSCs usually employ a mesoporous TiO 2 as the electron-transport layer (ETL), which also functions as the scaffold for depositing the perovskite absorbing layer. [4,5] Although it is criticized that the high-temperature (>450 °C) sintering process for the mesoporous TiO 2 layer makes the device manufacturing complex and energy consumptive, which also hinders the integration of PSCs with flexible substrates and electronics, such mesoscopic PSCs have been dominating the efficiency breakthroughs of PSCs from certified 14.1% in 2013 to 23.7% in 2019. [5-8] The latest 25.2% is highly possible also obtained by mesoscopic PSCs. [9] The ambipolar charge transport characteristics and long charge carrier diffusion length of lead halide perovskites offers the possibility of replacing the mesoporous ETL by a planar one, and constructing planar-structured PSCs with low-temperature (≤150 °C) processes. [10,11] For inverted (p-in) planar PSCs, there are plenty of options available for ETLs and hole-transport layers (HTLs), such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and phenyl-C61-butyric acid methyl ester (PC 61 BM), attributing to years of research on organic solar cells. [12,13] For regular (n-i-p) planar PSCs, compact TiO 2 layer was first used as the ETL, which soon aroused the attention on the anomalous hysteresis phenomenon for PSCs. [14,15] It was claimed that the low electron mobility of compact TiO 2 resulted in charge accumulations at the TiO 2 /perovskite interface and thus caused significant hysteresis. [16,17] Then, it was further found out that the electronic contact between the TiO 2 ETL and the perovskite layer played an essential role in the hysteresis behaviors of PSCs. [18] This is in agreement with the fact that the mesoporous TiO 2-based PSCs usually show much reduced hysteresis, [6,7] since the mesoscopically structured ETL can provide much larger surface area for contacting the perovskite absorber with stabilized properties. Along with the defects at the interfaces, ion migration and trap states in the perovskite layer have also been considered as the origin of the hysteresis Perovskite solar cells (PSCs) have rapidly developed and achieved power conversion efficiencies of over 20% with diverse technical routes. Particularly, planar-structured PSCs can be fabricated with low-temperature (≤150 °C) solution-based processes, which is energy efficient and compatible with flexible substrates. Here, the efficiency and stability of planar PSCs are enhanced by improving the interface contact between the SnO 2 electron-transport layer (ETL) and the perovskite layer. A biological polymer (heparin potassium, HP) is introduced to regulate the arrangement of SnO 2 nanocrystals, and induce vertically aligned crystal growth of perovski...

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The power conversion efficiency (PCE) of single-junction perovskite solar cells (PSCs) has continually risen over the last decade, from 3.

Bismuth-based solar cells have been under intensive interest as an efficient non-toxic absorber in photovoltaics. Within this new family of semiconductors, we herein report a new, long-term stable copper bismuth iodide (CuBiI ). A solutionprocessed method under air atmosphere is used to prepare the material. The adopted HI-assisted dimethylacetamide (DMA) co-solvent can completely dissolve CuI and BiI powders with high concentration compared with other organic solvents. Moreover, the high vapor pressure of tributyl phosphate, selected for the solvent vapor annealing (SVA), enables complete low-temperature (≤70 °C) film preparation, resulting in a stable, uniform, dense CuBiI film. The average grain size increases with the precursor concentration, greatly improving the photoluminescence lifetime and hall mobility; a carrier lifetime of 3.03 ns as well as an appreciable hall mobility of 110 cm V s were obtained. XRD illustrates that the crystal structure is cubic (space group Fd3m) and favored in the [1 1 1] direction. Moreover, the photovoltaic performance of CuBiI was also investigated. A wide bandgap (2.67 eV) solar cell with 0.82 % power conversion efficiency is presented, which exhibits excellent long-term stability over 1008 h under ambient conditions. This air-stable material may give an application in future tandem solar cells as a stable short-wavelength light absorber.