Efficient collection of photogenerated carriers by inserting double tunnel junctions in III-nitride p-i-n solar cells

The strain-induced piezoelectric polarization significantly affects the performances of III-nitride p-i-n solar cells. It tilts the energy-band of intrinsic InGaN layers towards a detrimental direction for drifting carriers, and induces a discontinuity at GaN/InGaN hetero-interfaces that hinders the collection of photocurrent. In this study, we have numerically demonstrated a general strategy to overcome the issues by inserting n⁺/p⁺/n⁺ and p⁺/n⁺/p⁺ GaN-based double tunnel junctions into the n- and p-sides of the device, respectively. The energy-band tilting in the intrinsic InGaN layer is hence absent, mainly attributed to high doping concentration of double tunnel junctions, screening piezoelectric polarization sheet charges, boosting the carrier collection efficiency. The impact of energy-barrier discontinuity is also alleviated due to the strong tunneling of photogenerated carriers, efficiently contributing to the photocurrent of the device. As a result, the incorporation of double tunnel junctions into devices offers the potential to realize efficient high indium III-nitride solar cells.