Impact of the III-V/Ge nucleation routine on the performance of high efficiency multijunction solar cells

TL;DR

This study investigates how different III-V nucleation routines on Ge substrates influence the performance of high-efficiency multijunction solar cells, revealing significant effects on open circuit voltage and subcell quality.

Contribution

It demonstrates the impact of nucleation routine parameters on solar cell performance, emphasizing the importance of growth process optimization for high-efficiency devices.

Findings

Open circuit voltage improved by up to 50 mV with optimized routines

Electroluminescence shows 25 mV VOC gain in Ge and GaInAs subcells

Growth stages influence both bottom and middle subcell performance

Abstract

This paper addresses the influence of III-V nucleation routines on Ge substrates for the growth of high efficiency multijunction solar cells. Three exemplary nucleation routines with differences in thickness and temperature were evaluated. The resulting open circuit voltage of triple-junction solar cells with these designs is significantly affected (up to 50 mV for the best optimization routine), whereas minimal differences in short circuit current are observed. Electroluminescence measurements show that both the Ge bottom cell and the Ga(In)As middle cell present a VOC gain of 25 mV each. This result indicates that the first stages of the growth not only affect the Ge subcell itself but also to subsequent subcells. This study highlights the impact of the nucleation routine design in the performance of high efficiency multijunction solar cell based on Ge substrates.