Carrier providers or carrier killers: the case of Cu defects in CdTe solar cells

TL;DR

This paper investigates how copper defects in CdTe solar cells can act both as carriers providers and killers, revealing complex defect behaviors that influence hole density and lifetime, and proposing strategies for optimal doping.

Contribution

It demonstrates that shallow Cu defects in CdTe can have dual roles, challenging the traditional view, and offers guidelines for balancing defect effects through thermodynamic and defect engineering strategies.

Findings

Increased Cu can raise hole density but also cause non-radiative recombination.

Optimal Cu doping requires balancing Cu concentration and incorporation temperature.

Strategies based on chemical potential and defect control improve CdTe solar cell performance.

Abstract

Defects play important roles in semiconductors for optoelectronic applications. Common intuition is that defects with shallow levels act as carrier providers and defects with deep levels are carrier killers. Here, taking the Cu defects in CdTe as an example, we show that shallow defects can play both roles. Using first-principles calculation methods combined with thermodynamic simulations, we study the dialectic effects of Cu-related defects on hole density and lifetime in bulk CdTe over a wide range of Cu incorporation conditions. Because CuCd can form a relatively shallow acceptor in CdTe, we find that increased Cu incorporation into CdTe indeed can help achieve high hole density; however, too much Cu can cause significant non-radiative recombination. We discuss two strategies to balance the contradictory effects of Cu defects based on the calculated impact of Cd chemical potential, copper defect concentrations, and incorporation temperature on lifetime and hole density. The results indicates that to optimize the Cu doping in CdTe, it is important to control the total amount of Cu incorporated into CdTe and optimize the match between the Cu incorporation temperature and the Cd chemical potential. These findings can help understand the roles of Cu defects in CdTe and the potential complex defect behaviors of relatively shallow defect states in semiconductors for optoelectronic applications.