Mechanism of bifunctional p-amino benzenesulfonic acid modified interface in perovskite solar cells

The n-type metal oxide SnO2 exists surface energy band bending due to massive vacancy oxygen. The bending will cause unnecessary electron accumulation and recombination at the interface between electron transport layer (ETL) and perovskite layer. Besides, there exist massive deep-level defects (PbI, Pbi, IPb) for solution-processed polycrystalline perovskite films, which will aggravate the energy band uncoordinated and non-radiative recombination, limiting device efficiency and stability. Herein, amphoteric linking molecule p-amino benzenesulfonic acid (ABSA) is firstly used to synergistically modify the interface between SnO2 ETL and perovskite layer. The acidic sulfonic acid groups in ABSA modify SnO2 ETL by inactivating the under-coordinated Sn ions, which reduces the energy band barrier on the surface of SnO2 film, increasing the conduction and reduces charge recombination. Besides, the alkaline amino groups also passivate the deep-level defects on surface of perovskite to lessen intermediate energy level and non-radiative recombination. The power conversion efficiency (PCE) of perovskite solar cells (PSCs) based on MAPbI3 is obviously increased from 18.02% to 20.32% after 0.10 mg ml−1 ABSA modification. Simultaneously, the modified devices show better stability due to improved perovskite crystallization and the reduced defects. The energy band model for SnO2 nanoparticle and interface between perovskite layer and SnO2 ETL is established to explain the interfacial engineering from a new physical perspective.