Origin of Hot Carriers in InGaN-Based Quantum-Well Solar Cells

In_xGa_1-xN/GaN multiple quantum-well (QW) (MQW) solar cells with x = 0.30 and 0.15 were characterized. The MQWs with x = 0.30 show deteriorated performances due to the inferior crystal qualities. At the temperatures above 200 K, the conversion efficiency (η) for x = 0.30 exhibits an abrupt increase led by the thermally activated carriers. Two potential origins are proposed for the hot carriers: 1) the native shallow donors in the MQWs and 2) the shallow QWs due to the compositional fluctuations. According to the distinct behavior of the device with x = 0.15, it is believed that the shallow QWs lead to the abrupt increase in η.