Electrical and Optoelectronic Properties Enhancement of n-ZnO/p-GaAs Heterojunction Solar Cells via an Optimized Design for Higher Efficiency

In this study, we report the fabrication of high quality AZO/NRs-ZnO/n-ZnO/p-GaAs heterojunction via a novel optimized design. First of all, the electrical proprieties of gallium arsenide (GaAs) substrates were enhanced via an optimized gettering treatment that was based on a variable temperature process (VTP) resulting in an obvious increase of the effective minority carrier lifetime (τeff) from 8.3 ns to 27.6 ns, measured using time-resolved photoluminescence (TRPL). Afterward, the deposition of a zinc oxide (ZnO) emitter was optimized and examined in view of its use both as a light trapping layer (antireflection) and as the n-type partner for the p-type (GaAs) substrate. Nanorod-shaped ZnO was grown successfully on top of the emitter, as an antireflective coating (ARC), to further boost the absorption of light for a large broadband energy harvesting. The interface state of the prepared heterojunction is a key parameter to improve the prepared heterojunction performance, thus, we used laser ablation to create parallel line microgroove patterns in the GaAs front surface. We studied the effect of each step on the performance of the n-ZnO/GaAs heterojunction. The results demonstrate a significant improvement in Voc, Jsc, fill factor (FF), and an obvious enhancement in the I-V characteristics, exhibiting good diode properties, giving rise to the photovoltaic conversion efficiency (η) from 8.31% to 19.7%, more than two times higher than the reference.