Enhancement of photovoltaic properties of CH₃NH₃PbBr₃ heterojunction solar cells by modifying mesoporous TiO₂ surfaces with carboxyl groups

In a new heterojunction solar cell employing CH₃NH₃PbBr₃ (MAPbBr₃) as the light absorber, we found that the introduction of a carboxylate monolayer on the mesoporous TiO₂ surfaces significantly enhances J_SC as well as V_OC. In particular, the presence of a bromoacetate monolayer at the interface of TiO₂/MAPbBr₃ remarkably increases the photovoltaic conversion efficiency (PCE) from 2.65% to 5.57% with J_SC of 5.411 mA cm⁻², V_OC of 1.372 V, and FF of 0.75. Time-resolved photoluminescence measurements indicate that the presence of the interfacial carboxylate groups expedites electron injection from MAPbBr₃ to TiO₂. Furthermore, according to pulsed light-induced transient measurements (PLITM) of photocurrent analysis, the lifetime of photoinjected electrons (τ_e) in the TiO₂ conduction band (CB) significantly increases with the passivation of the interface, implying the suppression of charge recombination as well.