Phenylethylammonium-formamidinium-methylammonium quasi-2D/3D tin wide-bandgap perovskite solar cell with improved efficiency and stability

Abstract

Wide bandgap (WBG) Sn perovskite solar cells (PSCs) efficiency enhancement is another sought after field and to resolve the issues related to fast crystallization, trap density and moisture induced oxidation of Sn2+ state in Sn perovskite, we endeavor the benefits of substituting hydrophobic phenylethlammonium (PEA+) cation into WBG PEAxFA0.75MA0.25-xSnI2Br through compositional engineering. We have realized that PEA+ substitution in WBG Sn perovskite led to form 2D/3D mixed perovskite and execute preferential orientation of 3D perovskite planes with controlled crystallinity. Our observation suggests that 2D perovskite phase here helps in merging the grain boundaries and reduce the rate of moisture penetration which ultimately controlled further oxidation of Sn2+. Also, the substitution of PEA+ in WBG Sn perovskite helps in modulating the band energies and aids to efficient electron injection from perovskite to transport layer. Compared to the 3D counterpart, 2D/3D perovskite exhibits slow lifetime decay (ravg = 1.25 ns), suppressed trap state density (1.7 x 1016 cm  3), improved band alignment with slower carrier recombination (r = 1217 mu s) and efficient charge extraction. As compared to FASnI2Br (PCE of 2.38%) and FA0.75MA0.25SnI2Br (PCE of 3.66%), our champion device PCE of 7.96% (Certified PCE of 7.84%) with Jsc of 16.89 mA center dot cm  2, Voc of 0.67 V and FF of 70.36% was achieved for PEA0.15FA0.75MA0.10SnI2Br, which is the highest PCE till date with compositional engineering strategy. The device kept under N2 atmosphere retained nearly original PCE after almost 1500 hrs and air stability of 300 hrs without encapsulation, indicating excellent stability.