Effect of well layer thickness on quantum and energy conversion efficiencies for InGaN/GaN multiple quantum well solar cells

- Effect of well thickness on InGaN/GaN MQW solar cell performance was studied.
- EQE and ECE showed the highest values at a specific well thickness.
- PL study indicated the generation of NRCs around a critical well thickness.
- The critical well thickness seemed to be considerably affected by growth conditions.

We investigated the effect of well layer thicknesses on the external quantum efficiency (EQE) and energy conversion efficiency (ECE) for InGaN/GaN multiple quantum well (MQW) solar cells grown on sapphire substrates by metalorganic chemical vapor deposition. The results indicated that EQE and ECE have maximum values at a specific well thickness. When the well thickness is sufficiently thin, EQE and ECE increase with an increase in the well thickness owing to an increase in light absorption. Then, once the well thickness surpasses a critical thickness, EQE and ECE begin to decrease owing to the influence of nonradiative recombination processes, which was indicated by the static and dynamic photoluminescence analyses. The critical well thickness probably depends not only on the MQW design but also on growth conditions. Further, we confirmed that the increased total thickness of the stacked well layers leads to increased light absorption and thereby contributes to the improvement of solar cell performance. A high short circuit current density of 1.34 mA/cm2 and a high ECE of 1.31% were achieved for a InGaN/GaN MQW solar cell with a 3.2-nm-thick InGaN well with total well thickness of 115 nm.