Efficiency limitations of chalcopyrite and kesterite solar cells

Abstract

We consider the efficiency limitations of Cu(In,Ga)(S,Se)2 as well as Cu2ZnSn(S,Se)4 champion solar cells based on published data and discuss the dominant recombination mechanism which limits the Voc of these devices. A CuIn1-xGaxSe2 solar cell with x≈0.3 is limited by recombination in the quasi-neutral-region including the back contact; we calculate a diffusion constant of electrons of about 0.5 cm 2 s -1 . Cells with x=1 (Cu-poor CuGaSe2) appear to be at the edge between recombination in the space-charge-region with very low bulk carrier lifetime and interface recombination. Solar cells based on Cu-rich Cu(In,Ga)(S,Se)2 as well as on kesterite Cu2ZnSn(S,Se)4 appear to be limited by interface recombination as the activation energy of the saturation current is smaller than Eg,a. Here, we discuss the impact of a type II band line-up both at the absorber/buffer interface and at the buffer/window interface.

Impact of air‐light exposure on the electrical properties of Cu(In,Ga)Se2 solar cells

“…The interface defect density impact depends on the degree of type inversion where a more complete inversion (lower interface hole concentration) can avoid interface recombination even in the presence of a higher defect density. Certainly, also the recombination rate of the competing recombination channels plays a role: If bulk recombination is very strong, the device may not run into interface recombination limitation . From the present results, we observe an induction of interface recombination by ALE and its suppression by HLS.…”

CdS and Zn1−xSnxOy buffer layers for CIGS solar cells

“…Several studies have optimized the CIGS/ZnSnO band alignment to have a positive spike in the order of 0.1 eV [25,51] but the ZnSnO/window layer has not been optimized. Moreover, it has been pointed out by Scheer et al that the conduction band alignment between the buffer layer and the window layer can lead to lower Voc and FF values [52]. Thus, our observations that the CIGS/ZnSnO interface has a lower number of defects is not contradictory with the possibility of a lower Voc compared with the CdS sample for two reasons: 1) the alignment between the buffer layer and the window layer can affect Voc and FF values and has not yet been optimized; 2) the cells are not dominated by interface recombination, so small changes to the interface will not cause significant changes to the cell performance.…”