Functional p-Type, Polymerized Organic Electrode Interlayer in CH₃NH₃PbI₃ Perovskite/Fullerene Planar Heterojunction Hybrid Solar Cells

Thermal curing of the styrene-functionalized 9,9-diarylfluorene-based triaryldiamine monomer (VB-DAAF) forms an ideal p-type organic electrode interlayer capable of resisting solvation of the polar precursor solution in fabricating methylammonium lead iodide (CH₃NH₃PbI₃) perovskite/fullerene (C₆₀) planar heterojunction hybrid solar cells. The polymerized VB-DAAF film exhibits a good energy level alignment with the valence-band-edge level of the CH₃NH₃PbI₃ perovskite to facilitate the transport of holes. The large energy barrier to the conduction-band-edge level of the CH₃NH₃PbI₃ perovskite effectively blocks electrons from reaching the positive electrode and reduces the photon energy loss due to recombination. The best-performing cell with the configuration of glass/indium-tin oxide/polymerized VB-DAAF/CH₃NH₃PbI₃ perovskite/C₆₀/bathocuproine/aluminum is free of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer to achieve an open-circuit voltage (V_OC) = 1.02 V, a short-circuit current (J_SC) = 18.92 mA/cm², and a fill factor (FF) = 0.78, corresponding to a power conversion efficiency (PCE) of 15.17% under standard 1 sun AM 1.5G simulated solar irradiation. The performance is much superior to the device applying the PEDOT:PSS interlayer with photovoltaic parameters of V_OC = 0.85 V, J_SC = 16.37 mA/cm², and FF = 0.74, corresponding to a PCE of 10.27%. Additionally, we had applied a UV-assisted process to polymerize the VB-DAAF film at relatively lower temperature and fabricate decent perovskite-based solar cells on the flexible substrate for real applications.