Acetamidinium substituted methylammonium lead iodide perovskite solar cells with higher open-circuit voltage and improved intrinsic stability.

We report Acetamidinium (AA) substituted methylammonium lead iodide perovskite solar cells. AA has a restricted C─N bond rotation, due to delocalized π-electron cloud over N─C─N bond and presence of an additional N─H--I bond (4H-bond in AA as compared to 3H-bond in MA). These bonding structures strengthen the electrostatic interaction and stabilizes the acetamidinium cation inside the perovskite matrix. AA, a larger cation, is substitutional only up to 10%. Devices made with 10% AA-substituted films show average Voc of 1.12 V, higher than the average Voc of 1.04 V in case of MAPbI3. This increase in Voc can be attributed to increase in carrier lifetime from 20 µs in case of MAPbI3 to 32 µs 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 (PCE) upto 480 h. Under same conditions, the PCE's of reference MAPbI3 devices reduced to 43% of their initial value in 480 h.