Suppressing ZnO-Induced Decomposition in Perovskite Solar Cells via Glycine-Based Chelation Strategy

Abstract

Organic-inorganic perovskite solar cells (PSCs) are a promising technology in renewable energy due to their high efficiency and low cost. The electron transport layer (ETL) plays a very important role in improving device performance by minimizing recombination losses and selective electron contact. In solar cells, zinc oxide (ZnO) is the most favored ETL due to its visible transparency, suitable energy level, excellent electron mobility, and structural flexibility. Nevertheless, the current application of ZnO in PSCs is restricted by the undesirable reverse decomposition reaction at the ZnO/perovskite (PVK) interface. The presence of surface hydroxyl (-OH) groups and interstitial zinc ions (Zn²⁺) speeds up the decomposition process. This process deteriorates the charge-collecting efficiency and PSC stability. By presenting a simple yet efficient technique for passivating the ZnO surface with chelating agents, glycolic acid (GlyAcid) and glycine hydrochloride (GlyHCl), we successfully addressed PVK decomposition at the ZnO/PVK interface. These chelating agents effectively passivated the ZnO surface through the suppression of -OH groups and the formation of metal complexes with interstitial Zn²⁺. It is found that, in comparison to GlyHCl, GlyAcid passivates the ZnO more effectively to form thermally stable optimum PVK on it with improved charge extraction, reduced defect density, larger grain size, and better energy level alignment. As a result, the ZnO/GlyAcid-based PSCs achieved a power conversion efficiency (PCE) of 23.09%, which is the highest PCE among the reported ZnO-based PSCs. Our research establishes a pathway to prevent PVK degradation on ZnO, allowing us to utilize its desirable ETL properties for PSCs.