Arsenic doped CdSeTe solar cells: Charge collection and Defects

Niranjana Mohan Kumar1, Srisuda Rojsatien1, Trumann Walker1, Tara Nietzold1, Barry Lai2, Arun K.M. Kanakkithodi3, Maria Chan2, Dan Mao4, Mariana Bertoni1 1Arizona State University, Tempe, AZ, United States /2Argonne National Lab, Lemont, IL, United States /3Purdue University, West Lafayette, IN, United States /4First Solar, Perrysburg, OH, United States

The selection of arsenic as a dopant has been an integral part of achieving high performing, 20.8%, polycrystalline CdTe solar cells. Although arsenic has significantly improved the long-term performance of the cells and the p-type doping levels reached inside the absorber, the activation ratio of dopant remains quite low, ~1%. Understanding the origins of this activation would aid in further bettering device performance. Herein, devices of two different activation levels but identical arsenic concentration are studied using nanoscale correlative X-ray microscopy in cross-section. Charge collection in cross-section shows a distinctive change between activation levels and the local environment around the As atom, as measured by X-ray absorption, shows the signature of several defects and phases that could be the culprit.