Commercial Production of the Group-V Doped Polycrystalline CdTe Source Material for the Next-Generation Photovoltaics

CdTe photovoltaic (PV) module performance has room to improve and can help the DOE in achieving its SunShot initiative. Improving the p-type doping and carrier lifetime in polycrystalline CdTe absorber material is critical to achieving PV cell efficiency to 25%. The current industrial supply chain consists of CdTe feedstock that undergoes treatments to help improve the material properties in effort to achieve a stable and efficient PV. Group-V doping has advantages over the current state-of-the-art where Group-V doping has shown to increase the hole density in CdTe which can improve the PV efficiency. CdTe feedstock is typically synthesized in vacuum-sealed quartz ampoules. Ampoules cannot be scaled beyond 3.0” – 4.0” diameter because beyond this ingot diameter, the risk ampoule failure becomes much greater. Doping with group-V elements pose further challenges where these elements have high vapor pressures and can cause ampoule rupture. Considering these challenges, high-pressure synthesis is the most promising technique for producing these materials – both raw CdTe and group-V doped CdTe, a process known asthe High-Pressure Bridgman (HPB). The team demonstrated CdTe can be doped with elemental arsenic in large batches (>5kg) using HPB. Sample materials were sent to research and industrial partners. PVs manufactured with these advanced materials performed similar to industry standard PVs. Group-V doping in CdTe will be further developed and a robust manufacturing program will be established. CdTe:As materials will be sent to industrial partners for validation. PVs will be manufactured from these materials and further advance the thin film CdTe technology. The HPB technique is a high-output and high-yield technique and is the only technique that can be used to produce arsenic-doped CdTe from elemental materials. The commercialization of the HPB process for production of CdTe feedstock materials will be significant to the thin film PV industry providing several advantages: (1) Volume. The HPB technology allows for large batching of CdTe and doped CdTe in a single growth run; (2) Sole Supply for Group-V doped CdTe. Due to the volatility of Gp-V materials, namely elemental arsenic, it is difficult to keep the material in crucible without a high backing pressure; (3) Cost. The HPB process is fast (~2 days start to finish), high volume production, minimal consumables, and minimal furnace monitoring, all contribute to radically reducing the cost of the feedstock CdTe material, on the order of >43%.