Optical Characterization and Photovoltaic Performance Evaluation of GaAs p-i-n Solar Cells with Various Metal Grid Spacings

Jenq-Shinn Wu,Ming-Cheng Kao,Yun-Guang Li,Hone-Zern Chen,Hung-Pin Hsu,Der-Yuh Lin

doi:10.3390/cryst9030170

Abstract

GaAs p-i-n solar cells are studied using electroreflectance (ER) spectroscopy, light beam induced current (LBIC) mapping and photovoltaic characterization. Using ER measurements, the electric field across the pn junction of a wafer can be evaluated, showing 167 kV/cm and 275 kV/cm in the built-in condition and at −3 V reverse bias, respectively. In order to understand the effect of the interval between metal grids on the device’s solar performance, we performed LBIC mapping and solar illumination on samples of different grid spacings. We found that the integrated photocurrent intensity of LBIC mapping shows a consistent trend with the solar performance of the devices with various metal grid spacings. For the wafer used in this study, the optimal grid spacing was found to be around 300 μm. Our results clearly show the importance of the metal grid pattern in achieving high-efficiency solar cells.

Highlights

Solar cells have drawn much research interest in recent decades due to their important role in renewable energy production [1,2,3]
The wavefunctions of electrons in the conduction band and holes in the valence band are in the form of Airy functions with the exponential tail extending into the semiconductor bandgap
As indicated by the arrows labeled 1–6, the extrema shift toward higher energy with increasing reverse bias is due to the increase of the built-in electric field

Summary

Introduction

Solar cells have drawn much research interest in recent decades due to their important role in renewable energy production [1,2,3]. Silicon is the predominant material used in the semiconductor devices of solar cells; solar cells based on III-V semiconductors exhibit superior energy conversion efficiencies. Many factors may affect the performance of solar cell devices. It has been reported that a high built-in electric field in the depletion region is helpful for photocarrier extraction from quantum wells [4,5]. It has been observed that a critical built-in electric field is necessary for an optimum carrier collection in multi-quantum well p-i-n diodes and a key factor in determining the open-circuit voltage (Voc ) [6]

Methods

Results

Conclusion