High-Performance Perovskite Solar Cells with Zwitterion-Capped-ZnO Quantum Dots as Electron Transport Layer and NH₄X (X = F, Cl, Br) Assisted Interfacial Engineering

The systematic advances in the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs) have been driven by the developments of perovskite materials, electron transport layer (ETL) materials, and interfacial passivation between the relevant layers. While zinc oxide (ZnO) is a promising ETL in thin film photovoltaics, it is still highly desirable to develop novel synthetic methods that allow both fine-tuning the versatility of ZnO nanomaterials and improving the ZnO/perovskite interface. Among various inorganic and organic additives, zwitterions have been effectively utilized to passivate the perovskite films. In this vein, we develop novel, well-characterized betaine-coated ZnO QDs and use them as an ETL in the planar n-i-p PSC architecture, combining the ZnO QDs-based ETL with the ZnO/perovskite interface passivation by a series of ammonium halides (NH₄X, where X = F, Cl, Br). The champion device with the NH₄F passivation achieves one of the highest performances reported for ZnO-based PSCs, exhibiting a maximum PCE of ~22% with a high fill factor of 80.3% and competitive stability, retaining ~78% of its initial PCE under 1 Sun illumination with maximum power tracking for 250 h.