Boosting charge extraction and efficiency of inverted perovskite solar cells through coordinating group modification at the buffer layer/cathode interface

In inverted perovskite solar cells (PSCs), effective modification of the interface between the metal cathode and electron transport layer (ETL) is crucial for achieving high performance and stability. Herein, sulfonated bathocuproine, commonly known as disodium bathocuproine disulfonate (BCDS), was employed as a cathode buffer layer to address the interfacial issues at the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/Ag interface. BCDS possesses the ability to form coordinate bonds with Ag electrodes. The utilization of the BCDS buffer layer enhanced the charge extraction capability at the cathode interface while simultaneously achieving interfacial defect passivation, improving interfacial contact, and increasing the built-in electric field. Consequently, a power conversion efficiency (PCE) of 25.06% was achieved. Furthermore, owing to the excellent film-forming uniformity of BCDS on PCBM, the stability of the device was also improved. After storage in dry air for more than 2000 h, the device maintained 96% of its initial efficiency. This work underscores the remarkable potential of tailoring coordination groups to enhance charge extraction efficiency at the ETL-cathode interface, unveiling a promising new frontier in buffer layer development and performance optimization strategies for PSCs.