Increasing Solar Efficiency of InGaN/GaN Multiple Quantum Well Solar Cells with a Reflective Aluminum Layer or a Flip-Chip Structure

Abstract

Multiple quantum well solar cells (MQWSC) have the potential to be a highly efficient alternative to tandem or cascade systems. However, in conventional multiple quantum well solar cells, the quantum well layer does not usually receive and absorb enough light. To increase the absorption in the quantum well layer of an InGaN/GaN multiple quantum well solar cell, a reflective aluminum layer has been proposed and investigated here. We also studied the use of a flip-chip structure to increase the effectiveness of the heat sink and to prevent the shading loss that occurs in top contact metal of InGaN/GaN MQWSCs. We found that In0.2Ga0.8N/GaN MQWSCs with a reflective aluminum layer are 9.8% more efficient than those without a reflective aluminum layer. Meanwhile, In0.28Ga0.72N/GaN MQWSCs with a reflective aluminum layer are 4% more efficient than those without a reflective layer. In0.28Ga0.72N/GaN MQWSCs were expected by their lower well bandgap to be more efficient than In0.2Ga0.8N/GaN MQWSCs, but they are not. The lower efficiency enhancement in In0.28Ga0.72N/GaN MQWSCs is attributable to the greater number of defects or recombination centers in the film with higher indium content. In0.2Ga0.8N/GaN and In0.28Ga0.72N/GaN MQWSCs with a flip-chip structure exhibit efficiency enhancements of 1.4% and 1.1%, respectively, over those without a flip-chip structure.