Effect of Se‐Free Annealing on Cesium Fluoride‐Treated Cu(In, Ga)Se2 Thin Films and Corresponding Solar Cells. Issue 2 (1st December 2021)

• Record Type: Journal Article
• Authors: Khatri, Ishwor; Santos, Pedro; Anacleto, Pedro; Sharma, Deepanjan; Belmoubarik, Mohamed; Nicoara, Nicoleta; Sugiyama, Mutsumi; Sadewasser, Sascha
• Is Part Of: Physica status solidi. Volume 16:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-01
• Subjects: annealing -- Cu(In, Ga)Se2 solar cells -- CsF-PDT -- solar cell efficiency -- Urbach energy -- Voc deficits; Solid state physics -- Periodicals; 530.4105
• DOI: 10.1002/pssr.202100462
• Languages: English
• ISSNs: 1862-6254

Abstract

Abstract : The effect of selenium‐free annealing on cesium fluoride (CsF)‐treated Cu(In, Ga)Se2 (CIGS) thin films is investigated and their solar cell performance is evaluated. Annealing of CsF‐treated CIGS thin films changes the surface morphology and the chemical composition, and reduces the Urbach energy. However, the full benefit of the reduced Urbach energies of the annealed samples is not obtained, because of an increased buffer/CIGS interface recombination as a consequence of re‐evaporation of the alkali‐containing layer from the surface region upon annealing. On the other hand, CsF‐treated CIGS thin films without any annealing after the post‐deposition treatment (PDT) preserve the alkali‐containing layer at the surface, thereby leading to an improved buffer/CIGS interface. Consequently, the open‐circuit voltage ( V OC ) and fill factor improve significantly in these devices. The Urbach energies of both annealed and nonannealed solar cells are calculated from external quantum efficiency measurement to understand their impact on V OC and V OC deficit. No correlation between the V OC deficit and the Urbach energies is observed. Abstract : It is found that Urbach energies do not correlate to the open‐circuit voltage ( V OC ) deficit in Cu(In, Ga)Se2 (CIGS) solar cells. It is shown that the surface properties of CIGS thin films play an important role in the V OC deficit. A suitable method for ex situ alkali‐metal treatment without using selenium vapor is identified.