Robust passivation of CdSeTe based solar cells using reactively sputtered magnesium zinc oxide

Magnesium zinc oxide (MZO, MgxZn1-xO) is a leading emitter for CdTe-based solar cells due to its transparency and the ability to tune its conduction band offset with the absorber. Devices employing alloyed cadmium selenide telluride (CST, CdSeyTe1-y) absorbers achieved high efficiency (>19%) using MZO deposited by reactive sputtering over a broad composition range (3.68-3.92 eV, x: 0.20-0.35). Minimal differences in implied and measured open circuit voltage indicate that the contacts are well passivated and highly selective across the spectrum of MZO employed. Device performance insensitivity to MZO composition, which is not observed in CdTe devices, is attributed to the formation of an oxygenated interface layer. Se volatility creates a group VI deficiency at the interface that drives O migration from the MZO into the absorber. This introduces conductivity in the emitter not present in its as-deposited state, contributing to the exceptional performance observed. It is shown that the quality of device passivation depends on the oxidation state of the as-deposited MZO such that intelligent control and management of the reactive sputtering process is required.

Automated summary

Magnesium zinc oxide (MZO) is a leading emitter for CdTe-based solar cells, achieving high efficiency when deposited on alloyed cadmium selenide telluride (CST) absorbers. The formation of an oxygenated interface layer during the reactive sputtering process contributes to the exceptional device performance.