Quantitative Evaluation on Electron Contacts in CdSe Solar Cells

Cadmium selenide (CdSe) is a promising top-cell material for tandem solar cells due to its high stability. However, the development of high-efficiency CdSe photovoltaics is hindered by significant contact losses at the device interfaces. While optimizing electron transport layers (ETLs) is a critical strategy for improving charge extraction, there is a lack of quantitative methods to evaluate contact material effectiveness in thin-film systems─specifically, contact resistivity─since conventional transfer length method (TLM) is hindered by lateral conductivity limitations and process incompatibility. Here, we introduce a modified TLM structure specifically tailored for thin-film architectures. Leveraging the n-type nature of CdSe and its propensity to form robust ohmic contacts with low-work-function metals, we circumvent these challenges, enabling the first quantification of contact resistivity on the electron collection side. Utilizing this method as a potent screening tool, we benchmark both standard (FTO, ZnO, CdS) and (Zn0.8Mg0.2O, ZnSe, ZnS) ETL materials. Guided by these quantitative insights, we engineered distinct device configurations that achieved record-low series resistance, a record-high fill factor of 62.8%, and power conversion efficiencies reaching 6.03%. This work establishes a standardized, quantitative methodology for interface engineering, providing a critical pathway for advancing high-efficiency CdSe photovoltaics.