InGaN-based multiple quantum well photovoltaic cells with good open-circuit voltage and concentration behavior

We report photovoltaic properties and concentration action of InGaN/GaN multi-quantum well (MQW) solar cells on c-plane sapphire substrate grown by metal-organic vapor phase epitaxy (MOVPE). The fabricated QW solar cells show a comparatively high open-circuit voltage of 2.06 at one sun and good concentration properties. The open circuit voltage (Voc) keeps increasing logarithmically with concentration ratio until 60 suns. The peak Voc of InGaN/GaN MQW solar cells, which have a predominant peak energy of 2.7 eV from electroluminescence (EL) measurements, is found to be 2.45 V when the concentration ratio reaches 333x. It was found that after an optimization of InGaN/GaN MQWs, the Voc can reach 2.31 V, displaying a bandgap to Voc difference (Eg/q-Voc) of 0.45 V. The obtained Eg/q-Voc is comparable to that of single-crystalline silicon or GaAs solar cells. The higher open-circuit voltage is mainly ascribed to extremely very low reversed saturation current density of around 10^-19 mA/cm², which could be attributed to the good crystal quality evidenced by TEM and HRXRD measurements. In addition, we give some discussions upon dependences of conversion efficiency and fill factor on concentration ratio for the fabricated MQW solar cells.