External bias effect on junction photoluminescence in CdS/CdTe solar cells

We study photoluminescence (PL) from the CdS/CdTe solar-cell junction region. We observed that applied external bias V does not change the spectral shape of the PL signal, but significantly affects the integral PL intensity I(V). It increases with moderate forward bias, tends to saturate when V is above the open-circuit voltage and is suppressed for reverse bias. In the region of forward-bias saturation I(V) is extremely sensitive to device stressing. We attribute the observed phenomena to the field-induced separation of the light-generated electrons and holes. At forward bias above the open circuit voltage, when the field effect is suppressed, PL intensity is dominated by non-radiative recombination.