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((3-x))(SCN)(x) (x = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN-), as a replacement for halides and as an inhibitor to suppress the Sn2+/Sn4+ 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)(2) showed about a threefold enhancement of the device efficiency (2.4%) relative to that of the best FASnI(3)-based device (0.9%), which we attribute to the improved suppression of the formation of Sn4+, retarded charge recombination, enhanced hydrophobicity, and stronger interactions between Sn and thiocyanate for FASnI(SCN)(2) than those for FASnI(3). After the incorporation of phenylethyleneammonium iodide (PEAI, 10%) and ethylenediammonium diiodide (EDAI(2), 5%) as coadditives, the FASnI(SCN)(2) device gave the best photovoltaic performance with J(SC) = 20.17 mA cm(-2), V-OC = 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.