Acetamidinium-Substituted Methylammonium Lead Iodide Perovskite Solar Cells with Higher Open-Circuit Voltage and Improved Intrinsic Stability

We report acetamidinium (AA)-substituted methylammonium (MA) lead iodide perovskite solar cells. AA has a restricted C-N bond rotation because of delocalized pi-electron cloud over the N-C-N bond and the presence of an additional N-H center dot center dot center dot I bond (4H-bond in AA as compared to 3H-bond in MA). These bonding structures strengthen the electrostatic interaction and stabilize the AA cation inside the perovskite matrix. AA, alarger cation, is substitutional only up to 10%. Devices made with 10% AA substituted films show an average V-oc of 1.12 V higher than the average V(oc )of 1.04 V in the case of MA lead halide perovskite (MAPbI(3)). This increase in V(oc )can be attributed to an increase in carrier lifetime from 20 mu s in the case of MAPbI(3) to 32 mu s for 10% AA-substituted films respectively. Devices with 18.29% champion and 16.3% average efficiency were fabricated for films with 10% AA. Degradation experiments confirm that the material stability also makes devices more stable; under ambient exposure (72 +/- 3% RH), devices with 10% AA retain 70% of their initial power conversion efficiencies (PCEs) up to 480 h. Under the same conditions, the PCEs of reference MAPbI(3) devices reduced to 43% of their initial value in 480 h.