Evaluation of Photoconversion Efficiency in InGaN/GaN MQW Solar Cells at High Temperatures
Heng-Sheng Shan, Ming-Hui Li, Xiaoya Li, Cheng-Ke Li, Shengwei Liu, Yifan Song, Yun-Jian Mei, Xiaodong Hao, Shufang Ma, Bingshe Xu
Abstract
The photoelectric conversion efficiency of InGaN/GaN multiple quantum well (MQW) solar cells has been investigated at high temperatures and the study revealed that their average value decreased from about 2.58% at room temperature to about 2.39% at a temperature of 500 °C. Atomic force microscopy (AFM) analysis indicated that the high-temperature treatment made the surface roughness of the material larger, and the crystal quality deteriorated. X-ray diffraction analysis showed that the full width at half-maximum (FWHM) value of the rocking curve and the degree of relaxation in the InGaN sample increased, indicating that the crystal quality in the active region had deteriorated. Photoluminescence (PL) spectroscopic measurements confirmed that the peak intensity decreased, and a red shift in the peak was observed in the PL spectrum. Moreover, scanning transmission electron microscopy (STEM) revealed an uneven distribution of indium components in the quantum well region after high-temperature treatment and that lattice distortion had taken place. Additionally, first-principles calculations were carried out, which also confirmed that the atomic movement led to a reduction in the band gap and to the red shift in the peak wavelength. The results of this study provided clear evidence that fluctuations of the indium components took place in the quantum well region under a high-temperature treatment at 500 °C, accompanied by lattice distortion. This led to an increase in the number of nonradiative recombination centers, which consequently led to the degradation of the photoelectric conversion efficiency in the fabricated InGaN/GaN MQW solar cells.