MOCVD of II-VI HRT/emitters for V_oc improvements to CdTe solar cells

CdTe solar cells were produced using metal organic chemical vapour deposition (MOCVD), which employed a (Zn,Al)S (AZS) high resistant transparent (HRT) layer at the transparent conducting oxide (TCO)/Cd(Zn)S emitter interface, to enable the higher annealing temperature of 440 °C to be employed in the chlorine heat treatment (CHT) process. The AZS HRT remained intact with conformal coverage over the TCO after performing the high CHT annealing, confirmed by cross-section scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX) characterisation, which also revealed the Cd(Zn)S emitter layer having been consumed by the CdTe absorber via interdiffusion. The more aggressive CHT resulted in large CdTe grains. The combination of AZS HRT and aggressive CHT increased open circuit voltage (Voc) and improved solar cell performance.