Theoretical study on potential performance of lattice-matched monolithic GaNP/GaNAsP/Si triple-junction solar cell

Abstract

A Si-based lattice-matched monolithic triple-junction (TJ) cell is presented by employing dilute nitride alloy GaN0.02P0.98 for top cell and III–N–V quaternary compound GaNAsP with a tunable bandgap for middle cell. Based on different models about the surface recombination velocity (S) and the minority carrier lifetime (τ) of III–V subcells, the theoretical performance of GaNP/GaNAsP/Si TJ cells is calculated with variable GaNAsP bandgaps and adjusted thicknesses of base layer in top and middle cells. The conversion efficiency of TJ cell has a strong relationship with S and τ due to the obvious influence of S and τ on the quantum efficiencies of III–V subcells. By adopting a superior model with S of electrons as 100 cm · s−1 and τ of electrons as 10 ns, a maximum efficiency of 41.53% is obtained when GaNAsP bandgap is 1.473 eV, and the optimum base thicknesses of top and middle cells are 1.2 μm and 2.0 μm, respectively. The calculation method and results would contribute to the study of multi-junction solar cell composed of III–N–V materials and low-cost Si substrate.