Comprehensive Model for Evaluating Voltage Losses and Performance Improvements in Thin-Film Photovoltaic Devices: Article No. 034019

Progress of state-of-the-art and next-generation thin-film photovoltaic devices is often stymied by open-circuit voltage (Voc) that is significantly lower than theoretical and practical limits. Yet, effectively diagnosing the primary sources of voltage loss remains challenging. Herein, a sequence of device-level characterization techniques and simulations are employed to identify and rank loss mechanisms. For the research-based Cd(Se,Te) device under study, most of the loss was at the front semiconductor heterointerface due to a clifflike conduction-band offset that lowered the recombination activation energy. Additional losses due to band tails were quantified by photoluminescence analysis. The latter provided the absorption coefficient and activation energy reduction associated with band tails as inputs to device models. Simulations showed that alleviating front-interface issues would improve Voc, but it would then be limited by bulk recombination. Further improvement of the bulk would then lead to back-contact limitations. Reducing band tails is beneficial in any circumstance. This analysis provides guidance for reaching toward the radiative Voc limit.