Investigation of properties of InGaN-based vertical-type solar cells with emission wavelengths in ultraviolet-blue-green regions

We investigate the properties of InGaN-based vertical-type solar cells having wavelengths ranging from the ultraviolet to green regions. It is well known that InGaN-based solar cells require a high indium composition to obtain high conversion efficiency. However, although InGaN-based solar cells with a high indium composition have been fabricated, their conversion efficiency has not sufficiently increased. Therefore, to further understand carrier transport, we measured the bias-dependent external quantum efficiency. For vertical-type green solar cells with a high indium composition, we confirmed that they have a higher short circuit current than other samples tested due to their broader overlapping region with the solar spectrum, though their fill factor remained low due to their high barrier height and strong piezoelectric field, which caused a reduction in the carrier tunneling rate.