Stability enhancement of GaInP/GaAs/Ge triple-junction solar cells using Al2O3 moisture-barrier layer

Abstract

A method to enhance the operational stability of GaInP/GaAs/Ge triple-junction (III-V) solar cells is proposed. To accomplish this, plasma-enhanced atomic layer deposition (PEALD) was employed, thereby forming a thin Al2O3 film as a moisture barrier layer. As observed, creation of a 50 nm Al2O3 layer demonstrated a water-vapor transmission rate (WVTR) of nearly 1.71 × 10−2 g/m2-day at 45 °C and 100% RH. Subsequent to Al2O3 deposition, solar cells were laminated with ethylene-vinyl acetate (EVA) and ethylene chloro-trifluoroethylene (ECTFE) films and exposed to conditions of 85 °C and 85% RH for 1000 h. As observed, when encapsulated within the 50 nm thin Al2O3 film, the III-V solar cells demonstrated greater stability over the said 1000 h period. On the other hand, III-V solar cells not encapsulated within the said Al2O3 films demonstrated an approximately 25% reduction in maximum power. Analysis results reveal that the observed degradation in III-V solar cell performance under high humidity conditions can be attributed to the oxidation of GaAs, which causes damage of the middle junction, and hence, drop in shunt resistance (RSH). Overall, III-V solar cells encapsulated within 50 nm Al2O3 demonstrated less than 1% drop in the power-conversion efficiency after 1000 h.