Development of Hybrid Pseudohalide Tin Perovskites for Highly Stable Carbon-Electrode Solar Cells.

Tin-based perovskites degrade rapidly upon interaction with water and oxygen in air because Sn-I bonds are weak. To address this issue, we developed novel tin perovskites, FASnI(SCN) ( = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN), as a replacement for halides and as an inhibitor to suppress the Sn/Sn oxidation. The structural and electronic properties of pseudohalide tin perovskites in this series were explored with quantum-chemical calculations by employing the plane-wave density functional theory (DFT) method; the corresponding results are consistent with the experimental results. Carbon-based perovskite devices fabricated with tin perovskite FASnI(SCN) showed about a threefold enhancement of the device efficiency (2.4%) relative to that of the best FASnI-based device (0.9%), which we attribute to the improved suppression of the formation of Sn, retarded charge recombination, enhanced hydrophobicity, and stronger interactions between Sn and thiocyanate for FASnI(SCN) than those for FASnI. After the incorporation of phenylethyleneammonium iodide (PEAI, 10%) and ethylenediammonium diiodide (EDAI, 5%) as coadditives, the FASnI(SCN) device gave the best photovoltaic performance with = 20.17 mA cm, = 322 mV, fill factor (FF) = 0.574, and overall efficiency of power conversion PCE = 3.7%. Moreover, these pseudohalide-containing devices display negligible photocurrent-voltage hysteresis and great stability in ambient air conditions.