III-V nitride material systems, which include AlN, GaN, InN, and their alloys, have been widely investigated due to their tunable energy bandgaps and application in light-emitting diodes (LEDs), laser diodes, and solar cells.1,2 The bandgap of InGaN material systems covers emission wavelengths from the near-ultraviolet (UV) to green regions, which essentially includes the entire functional range of the solar spectrum.3–5 To obtain a high conversion efficiency, most InGaN solar cells studies have been confined to the green region, requiring an indium content of about 15% to 30%.6–9 The efficiency of InGaN solar cells having an emission wavelength in the green region is high due to the high In composition, compared with those under a green wavelength, though their fill factor (FF) remains low due to their perceived poor crystal quality. In the early days of InGaN-based solar cells, most research focused on p-i-n solar cells having an intrinsic InGaN layer.10–13 However, it is difficult to fabricate the high-In composition and thick intrinsic InGaN layer required to increase the absorption due to the large lattice mismatch between InN and GaN.14 Furthermore, the polarization effects in p-i-n structures adversely reduce internal electrical fields inside intrinsic InGaN layers, leading to a lower open-circuit voltage (Voc) and shorter circuit current (Jsc) compared with multiple quantum well (MQW) solar cells.15 Accordingly, to maintain the high In composition and high crystal quality, several groups adopted InGaN/GaN MQW solar cells,16,17 though these solar cells still have a low Jsc and FF. Also, other groups recently reported the carrier transport in InGaN/GaN solar cells by barrier thickness and temperature.18,19 However, the carrier transport of InGaN/GaN solar cell by indium composition is not yet reported. In InGaN MQW structures having a high indium composition, carrier extraction also remains difficult due to the relatively high barrier height and strong piezoelectric field. The piezoelectric field is known to have an adverse effect on the tunneling rate, since it makes electrons and holes travel in opposite directions to which they contribute to the photocurrent.20 In order to overcome the piezoelectric field, several methods have been studied.21–24 Therefore, the further study of solar cells is essential in order to optimize InGaN solar cells requiring high efficiency.