Effects of ethylammonium and rubidium addition to guanidinium-based CH3NH3PbI3 perovskite photovoltaic devices prepared at 190 °C in ambient air

Effects of the addition of rubidium (Rb) and ethylammonium (CH3CH2NH3, EA) to guanidinium [C(NH2)3, GA]-based CH3NH3PbI3 perovskite solar cells were investigated. Lattice constants and the (100)-orientation of EA- and Rb-modified perovskite crystals increased compared with those of as-prepared perovskite. Abnormal increases of lattice constants of the GA- and EA-modified perovskite crystals prepared at 190 °C for 10 min in ambient air were also observed during the room temperature aging, which was due to crystal growth of the perovskites, and these features contributed to increased conversion efficiencies of devices based on the modified perovskites. Addition of GA and EA also effectively improved the photovoltaic properties of the device under indoor light conditions using white light-emitting diodes. First-principles calculations of the density of states and band structures indicated a reduction of the total energy through the addition of Rb or EA, suggesting that the current density was improved by the reduced band gap.