Bio-inspired interface engineering with sodium caseinate-doped bathocuproine (BCP) for stable and efficient inverted perovskite solar cells

Perovskite solar cells (PSCs) continue to attract considerable research interest due to their high power conversion efficiencies and compatibility with low temperature solution processing. In inverted PSC architectures, the inclusion of a buffer layer between the electron transport layer (ETL) and the metal electrode is essential for optimizing charge extraction and minimizing interfacial recombination losses. Bathocuproine (BCP) is commonly employed for this purpose; however, its influence on interfacial electronic properties and long term device performance remains an area of ongoing study. In this work, we explore a modified buffer layer approach by introducing sodium casinate from casein, a naturally occurring phosphoprotein with known affinity for metal ions, into the BCP layer. The addition of sodium caseinate was found to improve interfacial quality, lower trap state density, and enhance the electrical conductivity of the buffer layer. As a result, the power conversion efficiency (PCE) of the devices increased from 14.4% to 16.5%, accompanied by improved long term and operational stability. These findings highlight the potential of casein as a multifunctional additive for interface engineering in perovskite photovoltaics.