Compensation doping in InGaAs / GaAsP multiple quantum well solar cells for efficient carrier transport and improved cell performance

Abstract

A major challenge for multiple quantum well (MQW) solar cells is to extract sufficient photo-excited carriers to an external circuit through the MQW region under forward bias. The present study reports the effectiveness of compensation doping in the i-region, which includes MQWs, for more efficient transport of both electrons and holes. Unintentional p-type background doping occurs in GaAs by inevitable carbon incorporation during metal-organic vapor phase epitaxy, causing undesirable bending of the band lineup in the i-region of p-on-n devices. By cancelling this out by sulfur compensation doping to obtain a uniform electric field distribution, we achieved much a high carrier collection efficiency (CCE) >90% at the operating bias voltage regardless of the excitation wavelength, compared to < 50% without compensation doping. Consequently, cell performance was greatly improved, in particular showing an enhancement of the fill factor from 0.54 to 0.77, and degradation-free quantum efficiency within the GaAs absorption wavelength range. The photoluminescence (PL) intensity from the MQW increased as the CCE decreased at a large forward bias, and radiative recombination loss was significantly suppressed by compensation doping. Furthermore, time-resolved PL measurements indicated a much higher speed of carrier escape from the wells, showing a quicker PL decay time of 7 ns at 0.6 V, compared to 18–51 ns without compensation doping.