Impact of Er-Based Atomic Layer Deposited Upconverting Oxides on Si Solar Cell Surface Passivation

Crystalline silicon solar cells face fundamental limitations in infrared (IR) absorption leading to significant solar energy losses. Using upconverting (UC) rare-earth oxide layers is a potential solution to convert sub-bandgap photons into higher-energy photons that Si can absorb. However, integrating UC layers into solar cells can potentially affect surface passivation properties, which may result in recombination of photogenerated charge carriers at Si/UC interface. This study investigates the impact of atomic-layer-deposited mixed rare-earth oxide (Y,Er,Ho)2O3 and Er2O3 UC layers on the passivation quality of Si interface, deposited directly on Si substrate or on the conventional passivation layers, i.e., SiO2 and Al2O3. Findings reveal that direct deposition provides very weak passivation (tau eff approximate to 4.1 mu s) which does not improve with post-deposition annealing. Similarly, when deposited on top of SiO2 with optically relevant thickness, the resulting passivation is poor. However, UC layer on top of Al2O3 does not compromise the passivation performance, resulting in low surface recombination velocity of 1.5 cm s-1 for Er2O3 and 1.4 cm s-1 for (Y,Er,Ho)2O3. Consequently, the results indicate that it should be viable to integrate UC layer like Er2O3 into a state-of-the-art solar cell to improve sub-bandgap absorption without compromising the passivation properties.