Boosting Conversion Efficiency in Zn3P2/InP Solar Cells via Nanoscale Junction Engineering

Zinc phosphide (Zn3P2) shows great promise for next-generation photovoltaics made of earth abundant elements. To date, the poor crystal quality limited conversion efficiency to 4.4% for heterojunction devices and to 6% for Schottky junction solar cell. In this work, we report the fabrication and characterization of a Zn3P2 solar cell with a new record efficiency of 8%. The material quality is significantly improved by using selective area epitaxy (SAE) in conjunction with a post-growth annealing. The combination of J-V measurements and electron beam induced current mapping, alongside with optical and electrical simulations, outline the impact of the pattern dimensions on the device performances. In accordance with the findings of a recent simulation study, a decrease in the opening area fraction is associated with an increase in the VOC and a decrease in the JSC. This effect is more pronounced when the size of the openings is varied rather than the pitch. Our results suggest that the degradation of the VOC for large openings is predominantly attributable to the presence of misfit dislocations at the heterojunction interface. On the other hand, the reduced JSC for small openings is associated with a smaller electron diffusion length, which can be attributed to the current crowding effect. Finally, we confirm device stability under outdoor testing over a year, demonstrating the practical robustness of the optimized design.