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 (MAPbBr(3)) 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/MAPbBr(3) 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 MAPbBr(3) to TiO2. Furthermore, according to pulsed light-induced transient measurements (PLITM) of photocurrent analysis, the lifetime of photoinjected electrons (tau(e)) in the TiO2 conduction band (CB) significantly increases with the passivation of the interface, implying the suppression of charge recombination as well.