Optimizing carrier collection in solar cells through nanoscale junction design

Abstract

A key challenge in thin-film photovoltaics is achieving selective carrier collection that minimizes recombination losses while maintaining efficient charge extraction. This study presents a theoretical analysis of how reducing junction contact area can enhance the open-circuit voltage (V_OC) and the power conversion efficiency (PCE) in thin-film solar cells. Using a zinc-phosphide (Zn₃P₂) -based heterojunction as a model, we simulate the effect of geometrically minimizing contact via silicon-dioxide (SiO₂) layers with patterned holes. The smaller the contact area, the lower the reverse saturation current, which results in a significant increase in the V_OC up to 100 mV. However, the reduced contact area also increases the series resistance, thereby limiting the gain in PCE. This approach is especially effective with non-absorbing highly-doped transport layers, such as titanium-dioxide (TiO₂) (PCE gain up to 1.45%). This work underscores the importance of balancing reduced recombination with parasitic resistance and current crowding for optimal performance.