Realization of Nitride-Based Solar Cell on Freestanding GaN Substrate

A p–i–n solar cell composed of an undoped GaInN layer sandwiched between n- and p-type GaN layers was grown on a freestanding c -plane GaN substrate and a c -plane sapphire substrate covered with a low-temperature-deposited buffer layer. The open-circuit voltage is 2.23 V, the fill factor is 61%, the short-circuit current density is 1.59 mA/cm 2 , and the conversion efficiency of the solar cell on the GaN substrate is 1.41% using a solar simulator (1.5 suns). Compared with the solar cell characteristics of the device grown on the sapphire substrate, pit density markedly decreases. As a result, shunt resistance increases, suppressing the open-circuit voltage drop.