Ex situ bismuth doping for efficient CdSeTe thin-film solar cells with open-circuit voltages exceeding 900 mV

Abstract

The focus of CdSeTe thin-film solar cell doping has transitioned from copper (Cu) doping to group V doping. In situ group V doping has resulted in a new record power conversion efficiency (PCE) of 23.1%, with open-circuit voltages (V_OCs) exceeding the 900 mV mark. Here, we report that ex situ bismuth (Bi)-doped CdSeTe thin-film solar cells show V_OCs exceeding 900 mV and a champion PCE of 20.6%. Characterizations revealed that the Se-rich CdSeTe region near the front junction promotes Bi ions to occupy the anion sites and dope this region weakly p-type. Bi ions in the CdTe-dominating back surface region occupy the cation sites and are oxidized. This ex situ Bi doping with BiF₃ as a dopant precursor offers several advantages, including simplicity, high tolerance to the processing environment, and no requirement of additional Cd vapor or special activation processes, making it highly adaptable for researchers to explore efficient Bi-doped CdSeTe thin-film solar cells.