Semi-polar InGaN/GaN multiple quantum well solar cells with spectral response at up to 560Â nm

We demonstrate a series of semi-polar InGaN/GaN multiple quantum well (QW) based solar cells with high indium content, where operating wavelength ranges from green to amber. These devices are grown on high crystal quality overgrown semi-polar GaN templates. The spectral response at a long wavelength of up to 560 nm has been obtained. With increasing indium content of QWs (i.e., increasing operating wavelength), the external quantum efficiency increases across a wide range of wavelength. Compared to the device with green QWs, the devices with amber QWs exhibits significantly increased short-circuit current density and conversion efficiency, achieving a current density of 1.4 mA/cm2 and an enhancement factor of 170% under the AM 1.5G illumination. Photoluminescence excitation measurements show that it is attributed to enhanced light absorption in InGaN QWs by pushing the QW absorption edge towards longer wavelength. Furthermore, another series of InGaN QW solar cells is investigated with different indium contents in the three QWs of each device. The device with two yellow QWs on the top and one blue QW underneath exhibits spectral response at a long wavelength of up to 560 nm, whereas the device with one blue QW on the top and two yellow QWs underneath shows no response beyond 460 nm. It reveals that the InGaN QW closest to the top p-type GaN plays a determined role in the spectral response on the long wavelength side.