Determination of dominant recombination paths in Cu(In,Ga)Se2 thin-film solar cells with ALD-ZnO buffer layers

CuIn1-x,GaxSe2 (CIGS) and CuInSe2 (CIS) thin-film solar cells, with ZnO buffer layers deposited by Atomic Layer Deposition (ALD), are examined with respect to dominant recombination path. They are compared with reference cells with US buffer layers. The principal method of examination is temperature-dependent J-V characterization (J(V)(T)) and the analysis of the J(V)(T) data has been modified in order to more reliably discern the, dominant recombination path. Compared to the CIS cells with the traditional CdS buffer layer, the CIS cells with ALD-ZnO buffer layer exhibit the same dominant recombination path, i.e., recombination in the bulk of the absorber. For the CIGS cells (with [Ga]/([Ga]+[In])=0.3), however, the analysis of the cells with ALD-ZnO buffer points to dominant interface recombination, while the CdS buffer cells are dominated by bulk recombination. For CIGS, the difference between the recombination in ALD-ZnO and US cells is consistent with the negative conduction band offset found by photoelectron spectroscopy in these ALD-ZnO cells in a previous study. This offset leads to increased interface recombination. For CIS/ALD-ZnO, it was previously found that there is no negative conduction band offset since the conduction band minimum of the absorber is lower. Consistently there is no difference in dominant recombination path between ALD-ZnO buffer cells and traditional US buffer cells. (c) 2004 Elsevier B.V. All rights reserved.