Highly Stable Thiophene Perovskite Enabled by an Oxygen-Containing Moiety for Efficient Photovoltaics

We present oxygen-containing 2D perovskites, ((TPM)x(TFF)1–x)2(CH3NH3)n−1PbnI3n+1 (TPM = C4SH3CH2NH3, TFF = C4OH7CH2NH3, x = 0.5 or 0.75, and n = 1–4), which have two species of cations between the inorganic slab. The 2D layered (TPM)2(CH3NH3)n−1PbnI3n+1(n = 1–4) perovskites have a high polarizability of the sulfur atom and a π-conjugated electron-rich aromatic ring structure. However, it still shows instability under ambient condition. The 2D (TPM)2(CH3NH3)n−1PbnI3n+1(n = 1–4) perovskites incorporated an oxygen-containing molecule, TFF, which has high durability toward the environmental system. Structural characterization by single-crystal X-ray diffraction reveals that the ((TPM)x(TFF)1–x)2(CH3NH3)n−1PbnI3n+1 perovskites exhibit a slight structural distortion of the equatorial Pb–I–Pb bond angles compared to those in the (TPM)2(CH3NH3)n−1PbnI3n+1 (n = 1–4) perovskites. However, their band gaps are almost the same, because the interlayer spacing between the inorganic layers for the TPM and TFF compounds has approximately the same spatial distance. Furthermore, it was observed that the long emission lifetime in the ((TPM)x(TFF)1–x)2(CH3NH3)n−1PbnI3n+1 perovskite series from the self-trapped excitons is due to the more distorted structure. We fabricated photovoltaic devices that utilize these materials as light absorbers, and they exhibit promising performances with the highest power conversion efficiency of 10.01% for (TPM0.75TFF0.25)2(MA)3Pb4I13-based devices.