Photovoltaic response of InGaN/GaN multi-quantum well solar cells enhanced by inserting thin GaN cap layers

• The spectral response of InGaN/GaN MQW solar cells with different LT-cap layer thicknesses was investigated.
• Inserting a 0.75 nm-thick LT-cap layer can remarkably improve photovoltaic response of InGaN/GaN MQW solar cells.
• A macroscopic optical method was used to investigate the microscopic localization effect and defect density in InGaN QW.
• Strong localization effect in InGaN QW is harmful for the formation of high efficiency InGaN/GaN MQW solar cells.

Structural properties and photovoltaic response of InGaN/GaN multi-quantum well (MQW) solar cells with low temperature grown GaN cap (LT-cap) layers were investigated. It is found that inserting a thin LT-cap layer (around 0.75 nm) between each InGaN quantum well (QW) and GaN quantum barrier (QB) can remarkably improve photovoltaic response of InGaN/GaN MQW solar cells. This is attributed to the increased optical absorption of InGaN QWs due to higher indium content and thicker InGaN QWs thickness when LT-cap layers are added. However, if the LT-cap layer is too thick, the localization effect is enhanced and the defect density of InGaN QW layers will increase too much. Both of them will result in a reduced photovoltaic response of InGaN/GaN MQW solar cells.