Activation of Group-V doped Cadmium Telluride Photovoltaics

Doping of CdTe photovoltaics (PV) is essential to fabricate a high efficiency device. Traditionally, CdTe PV is doped with Cu, however, Cu doping cannot enhance hole density greater than 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> order. The excess Cu in the devices creates interstitial defects and limits the open-circuit voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</inf>) of the device. Alternatively, CdTe solar cells are doped with group V elements such as arsenic (As), phosphorus (P), antimony (Sb) and bismuth (Bi). The idea is to enhance the hole carrier density, and increase the quasi-fermi level splitting, and thus improve the V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</inf> of the device. This is usually carried out in-situ and ex-situ doping process. The In-situ group-V doping process brings its own challenges for the activation of group V dopants. Here, we discuss the activation of a group V (As) doped CdSe/CdTe photovoltaic devices. Our initial results indicate that the carrier density increased up to 3x10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> with an activation ratio of ~ 1%, and device efficiency close to 16% for thermally evaporated CdTe devices.