Synergistic passivation of MAPbI3 perovskite solar cells by compositional engineering using acetamidinium bromide additives

Abstract For the global commercialization of highly efficient and stable perovskite solar cells (PSCs), it is necessary to effectively suppress the formation of various defects acting as nonradiative recombination sources in perovskite light-harvesting materials. Interfacial defects between the charge-selective layer and the perovskite are easily formed in the solution process used to fabricate perovskite films. In addition, owing to the difference in thermal expansion coefficients between the substrate and the perovskite film, internal residual tensile stress inevitably occurs, resulting in increased nonradiative recombination. Herein, a simple compositional engineering scheme for realizing efficient and stable PSCs, which incorporates acetamidinium bromide (AABr) as an additive into the MAPbI3 lattice, is proposed. As an additive, AABr has been found to provide synergistic multiple passivation for both internal and interfacial defects. AABr was found to effectively release the tensile strain of the MAPbI3 film by forming a structure stabilized by NH–I hydrogen bonds, as evidenced by calculations based on density functional theory (DFT). Furthermore, the incorporated AABr additives created a charge carrier recombination barrier to enhance charge collection capability by reducing interfacial defects. Accordingly, a power conversion efficiency (PCE) of 20.18% was achieved using a planar device employing AABr-incorporated MAPbI3. This was substantially higher than the 18.32% PCE of a pristine MAPbI3-based device. Notably, unencapsulated PSCs using AABr-incorporated MAPbI3 absorbers exhibited excellent long-term stability, maintaining >95% of initial PCE up to 1200 hours in ambient air.