Controlled activation of ZnTe:Cu contacted CdTe solar cells using rapid thermal processing

Back contacts can significantly limit CdTe solar cell performance, reducing both open circuit voltage (Voc) and fill factor (FF). Copper is an essential component of effective back contacts, but its presence in the CdTe absorber creates detrimental recombination centers. Rapid thermal processing (RTP) is demonstrated as a highly effective approach for reducing back contact barriers in CdTe solar cells contacted with ZnTe:Cu buffer layers, substantially improving both FF (>73%) and Voc (>850mV). Current density and quantum efficiency remain essentially unchanged, but a five-fold increase in minority carrier lifetime is observed which is attributed to passivation of recombination sites in the back contact region. Quantitative analysis of secondary ion mass spectrometry shows that the majority of Cu segregates to the Au metallization layer and that the ZnTe buffer appears to inhibit the Cu diffusion into CdTe. 3D imaging of the back contact region using atom probe tomography shows that optimized devices are characterized by preferential segregation of copper to both the Au|ZnTe and CdTe|ZnTe interfaces, perhaps in the form of CuxTe. With its low thermal budget the RTP process has been successfully applied to multiple device architectures. [Display omitted] •RTP is demonstrated as an effective approach to activate ZnTe:Cu back contacts.•Improvements in τ, Voc and FF help elevate device efficiencies to >16%.•SIMS shows that the ZnTe buffer inhibits Cu diffusion into the bulk.•Cu preferentially segregates to both the metal|ZnTe and ZnTe|CdTe interfaces.