Solvent-mediated surface modification of electron transport layers for efficient PbS quantum dot solar cells

Abstract

Interface engineering plays a crucial role in determining the performance of lead sulfide (PbS) colloidal quantum dot (CQD) solar cells. Defects and surface states at the PbS–electron transport layer (ETL) interface significantly influence charge extraction and recombination processes. ZnMgO nanoparticles are widely employed as ETLs due to their high electron mobility and facile synthesis; however, excess surface hydroxyl (–OH) groups introduce interfacial trap states that impede efficient electron extraction. In the present work, we have overcome these limitations through solvent-mediated surface modification of ZnMgO surfaces, which utilizes a simple toluene treatment. Untreated ZnMgO films have high surface energies and low wettability, resulting in a lack of uniform coverage of PbS CQD films, which leads to an undesirable increase in the rate of recombination. Toluene treatment allows the surface hydroxyl groups to be removed, which was validated by morphological analysis and also analyzed via density functional theory calculations. Such surface modification is shown to suppress trap-assisted recombination and promotes efficient transfer of electrons, which leads to a significant improvement in V_oc, J_sc, and FF. As a result, the power conversion efficiency increased from below 1% in untreated devices to 6.73% upon toluene treatment of the ZnMgO ETL. These findings offer a straightforward and powerful approach to streamline efficient ETL/CQD interface engineering with minimized interfacial flaws and realize the full potential of PbS CQD solar cells in high-efficiency photovoltaic applications.