Lead Telluride Nanowires for Surface Passivation in Cadmium Telluride Photovoltaics

Abstract

Cadmium telluride (CdTe) is one of the leading technologies in thin-film solar cells; however, its open-circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> ) is limited by defects associated with polycrystalline nature, carrier concentration, and interfaces. To overcome the deep work function of the CdTe absorber and create a passivating back contact interface, a lattice-matched and highly doped p-type material is needed to function as a buffer layer between the CdTe and a highly conductive electrode. Here, we report that lead telluride (PbTe) nanowires (NWs) serve to passivate the CdTe back contact, enhancing the optoelectronic properties and device performance. The steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements showed improved PL intensity and minority carrier lifetime for devices utilizing a PbTe NW back buffer, consistent with surface passivation. Additionally, the devices employing PbTe NWs showed improved V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> and fill factor (FF). For instance, implementation of PbTe NWs as a passivating layer to CdS/CdTe solar cells yielded a photoconversion efficiency of 14.8% (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> = 855 mV and FF = 77.3%), whereas the control device reached 14.0% (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> = 840 mV and FF = 75.9%). This improvement in V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> and FF is consistent with the reduction in both back-barrier height and recombination losses observed for devices with the PbTe NW back buffer.