On the Role of Interfaces in Planar-Structured HC(NH₂)₂PbI₃ Perovskite Solar Cells

Planar-structured HC(NH₂)₂PbI₃ (FAPbI₃) perovskite solar cells were prepared via a two-step deposition process. To investigate the role of interface, the perovskite morphology was intentionally modified by varying HC(NH₂)₂I concentration. Surface and grain sizes of the deposited FAPbI₃ became rougher and larger as the HC(NH₂)₂I concentration decreased from 58.2 to 40.7mM. Average photocurrent was improved but photovoltage deteriorated slightly with decreasing concentration. Consequently, the average efficiency was improved from 7.82% to 10.70% and the best efficiency of 12.17% was obtained at 40.7mM. Photoluminescence (PL) at TiO₂/FAPbI₃ interface was reduced with decreasing concentration, which was, however, reversed at FAPbI₃/spiro-MeOTAD one. By correlating PL data and the photovoltaic performance, we concluded that the TiO₂/perovskite interface plays a crucial role in determining photocurrent while the perovskite/spiro-MeOTAD interface is important in governing photovoltage. Focus on interfaces: A planar-junction perovskite solar cell composed of TiO₂/formamidinium lead iodide(FAPbI₃)/spiro-MeOTAD is fabricated, in which interfaces of FAPbI₃ in contact with TiO₂ and spiro-MeOTAD are modified to investigate the role of each interface. The TiO₂/FAPbI₃ interface is found to play an important role in determining short-circuit photocurrent, while the FAPbI₃/spiro-MeOTAD interfacial role is involved in governing open-circuit voltage.