Efficiency Loss Due To Defects In AlGaAs/GaAs Hetero-junction Solar Cell

Abstract

The principle of Energy conservation is -Energy can neither be created nor be destroyed, it can only be converted from one form to another. So energy conversion efficiency is a major issue for photovoltaic cells. Researchers are continuously trying to improve the efficiency level of photovoltaic devices by introducing new materials and advanced concepts. The target is to reach a high efficiency level within affordable cost, which will lead to a mass generation of electricity using photovoltaic devices. In this work, a III-V hetero-junction solar cell has been introduced and characterized, which uses an AlxGa1-xAs/GaAs hetero-junction as the working p-n junction. ADEPT, 1D simulation software was used throughout the whole work for the simulation of light J-V characteristics for different designs. Energy conversion efficiency for each design was calculated from its corresponding light J-V characteristics curve. An illumination level of 1000 W/m2 (AM1.5G standard) and a concentration level of 1 sun was considered for all the simulations in the work. The photovoltaic cell has an non- p structure, where the n-type AlxGa1-xAs layer acts as an base, and the p-type GaAs layer serves as the emitter. The base thickness was kept at 2 μm. Germanium (Ge) substrate (p-doped) was used for the structure. We used ADAPT software for simulating J-V curve. From the curves, we got Open circuit voltage Voc and short circuit current Isc . Then, from these, Fill Factor and efficiency was calculated for each mole fraction of 0 to 1 with a gap of 0.01. And, then generation on electron hole pair was calculated. Then parameters including absorption coefficient α(λ), number of photons φ0 were calculated for a mole fraction of 0 to 1 with a gap of 0.01 . Short circuit current and open circuit voltage were calculated and from that, fill factor and efficiency was calculated for each mole fraction from 0 to 1 with a gap of 0.01. Then, simulated efficiency and theoretical efficiency were plotted against mole fraction from 0 to 1. And then, efficiency loss vs. mole fraction was plotted.