A thioacetamide additive-based hybrid (MA0.5FA0.5)PbI3 perovskite solar cells crossing 21 % efficiency with excellent long term stability

An additive in hybrid perovskite is playing a vital role in the increment of power conversion efficiency (PCE), stability, and reproducibility of perovskite solar cells (PVSCs). Although, single-phase α-FAPbI3 perovskite has an ideal band gap but is continuously transforming to δ–FAPbI3, which is non-photoactive. Here, we controlled the methylammonium (MA) and formamidinium (FA) ratio in the (MAxFA1-x)PbI3 perovskite composition and tuned its morphology with the help of the thioacetamide (TAA) Lewis base additive. The optimum MA:FA ratio and fine-tuning of TAA additive result in a highly crystalline, large grain size and smooth surface of the (MA0.5FA0.5)PbI3 perovskite film. These highly uniform thin films with 850 nm grain size offered a superior interaction between the perovskite material and the electron transport layer (ETL) and a longer lifetime yielding a high PCE. The (MA0.5FA0.5)PbI3+1% TAA-based champion device exhibited the highest PCE of 21.29% for a small area (0.09 cm2) and 18.32% PCE for a large area (1 cm2). The TAA-assisted devices exhibited high stability with >85% retention over 500 h. These results suggest that the (MA0.5FA0.5)PbI3 along with the 1% TAA additive is a promising absorber layer that can produce >21% PCE.