Impact of Strain on the Performance of InGaN-based Multij unction Solar Cell

Abstract

Strain issue and its impact on the performance of InGaN-based multijunction solar cell (MJSC) is addressed for the first time in the present research work. The route of strain in MJSC is identified to be due to the change in lattice constants in different layers of subcell grown epitaxially with bandgap stepping. Using multi-layered strain model, the state of strain and its magnitude is determined for three kinds of MJSC structures named as MJSC- 1, MJSC-2 and MJSC-3. The results are expressed in terms of subcell thickness 80nm, lOOnm and 120nm and number of subcells 3, 5 and 7. It is found that the magnitude of MJSC position-dependent strain is strongly dependent on the subcell thickness and decreases with increasing the layer thickness. Further, the position-dependent strain increases with increasing the number of subcells. With the combination of MJSC position-dependent strain and deformation potentials, the strain-induced energy bandgap modification is determined under tensile strain condition. Finally, including the strain effect the efficiencies of different MJSC structures are evaluated and found to be lower with that of reported without taking into account of strain. The detraction of efficiency is identified to be due to the open circuit voltage which decreases under tensile strain condition. Among the MJSC structures studied here, MJSC-3 with 7-layers is less efficient and it's efficiency decreases upto 3.01% when strain effect is taken into consideration.