Electron transport layers in thin-film solar cells: Materials, interfaces, and device performance

Thin-film photovoltaic technologies such as perovskite, CIGS, CdTe, and organic solar cells have gained considerable attention due to their potential for low-cost, flexible, and lightweight energy conversion solutions, necessitating advanced components to optimize device efficiency and stability. A complex component in these devices is the electron transport layer (ETL), which governs charge extraction and recombination dynamics, directly impacting overall performance. Despite numerous advances, there remains a lack of unified understanding of ETL materials and interface engineering, highlighting a research gap in cross-technology comparative studies and universal design principles. This review addresses this gap by systematically analyzing ETL materials, interface modification strategies, and deposition techniques reported in recent literature across multiple thin-film PV systems. Employing a comprehensive cross-technology approach, the study synthesizes experimental, theoretical, and practical insights to identify emerging materials. Key findings emphasize the effectiveness of interface engineering methods such as surface passivation, energy level alignment, and self-assembled monolayers in enhancing charge transport and reducing recombination losses. This work significantly provides a framework to overcome challenges related to scalability, cost, and compatibility with flexible and tandem architectures, thereby guiding future development of universal ETLs and innovative design strategies to accelerate the commercialization and performance of thin-film solar cells.