Field modulation in Na-incorporated Cu(In,Ga)Se2 (CIGS) polycrystalline films influenced by alloy-hardening and pair-annihilation probabilities.

ABSTRACT

The influence of Na on Cu(In,Ga)Se2 (CIGS) solar cells was investigated. A gradient profile of the Na in the CIGS absorber layer can induce an electric field modulation and significantly strengthen the back surface field effect. This field modulation originates from a grain growth model introduced by a combination of alloy-hardening and pair-annihilation probabilities, wherein the Cu supply and Na diffusion together screen the driving force of the grain boundary motion (GBM) by alloy hardening, which indicates a specific GBM pinning by Cu and Na. The pair annihilation between the ubiquitously evolving GBMs has a coincident probability with the alloy-hardening event.PACS 88. 40. H-, 81. 10. Aj, 81. 40. Cd.