On the design and performance of InGaN/Si double-junction photocathodes

Through a combined theoretical and experimental study, we have investigated the synthesis and performance characteristics of InGaN/Si double-junction photoelectrochemical (PEC) water splitting devices, which promise a theoretical solar-to-hydrogen conversion efficiency ∼30% under AM 1.5G one-sun illumination. The double-junction photocathodes consist of a p+-InGaN top light absorber and a Si bottom p-n junction, which are connected through a nanowire tunnel junction. The effect of indium composition of the top light absorber as well as the impact of p-type Mg dopant incorporation on the PEC performance was studied. Experimentally, the sample with 32% indium composition showed a maximum photocurrent density of ∼9 mA/cm2 at 0.4 V vs reverse hydrogen electrode (RHE) with applied bias photon-to-current efficiency (ABPE) of ∼9.5%. An optimum p-type doping level ∼1 × 1017 cm−3 was also identified, which results in the best device performance as a result of optimum surface band bending as well as vertical charge carrier (hole) transport. These results also show a good agreement with our theoretical analysis. This work provides significant insights in advancing the design and development of high efficiency PEC devices for artificial photosynthesis using industry ready materials, e.g., Si and GaN, to achieve large-scale, low-cost onsite hydrogen fuel production.