INDUSTRY TRACK: Advances of CdTe Photovoltaics

INDUSTRY TRACK: In recent years, CdTe solar cell research has transitioned to p-type doing using group-V elements such as As or P. Compared to traditional Cu-doping, group-V doping can result in two orders of magnitude higher carrier concentrations, implying an open-circuit voltage gain of more than 100 mV. In addition, the long-term degradation rate, and temperature coefficient of CdTe solar cells are further reduced, suggesting higher energy yield at the same name plate efficiency/wattage.

In 2023, efficiency OF group-V doped devices surpassed Cu-doped CdTe solar cells for the first time. To date, we have certified >23.1% efficiency at NREL. In addition, 917 mV was achieved with absorber band gap of 1.39 eV. The gain is largely due to improvement of V_oc and FF compared to Cu-doped devices. Engineering the interface between CdTe and ZnTe leads to reduced interface recombination. An optimized selenium profile in part contributed to lower voltage deficit. Other improvements include a wide bandgap metal oxide buffer layer in front of the absorber and inserting an optical reflector after the back contact to increase near band-edge QE. In addition, we also demonstrated reduced microscopic non-uniformity via lower As dosage or phosphor incorporation. Approximately 20% of As dopant activation ratio was achieved in poly-crystalline CdSe_xTe_1-X. Pathways for further improvement include enhanced passivation at back contact interface, and reduction of non-radiative recombination in absorber via better activation of group V dopants, reduced potential fluctuations, and identification and mitigation of defects in the absorber.