Impact of varied sulfur incorporation on the device performance of sequentially processed Cu(In,Ga)(Se,S)₂ thin film solar cells

Abstract

In order to improve the performance of chalcopyrite Cu(In 1 À x ,Ga x )(Se 1 À y S y ) 2 solar cells, the implementation of a bandgap widening at the absorber/buffer interface via an increase of the [S]/[S þ Se] ratio is investigated. In this work we examine industrially processed samples, which were fabricated via the deposition-reaction process with varied H 2 S pressure during rapid thermal processing (RTP). Precursors which were exposed to a crucial amount of sulfur during the RTP step resulted in samples with significantly improved device performance. The increase of the open circuit voltage by about 150 mV cannot sufficiently be explained by bandgap widening.Observation of a strongly reduced saturation current density and ideality factor in intensively sulfurized samples suggest subdued recombination via mid-gap defect states located in the space charge region. This hypothesis is supported by results of deep-level transient spectroscopy measurements, which show that in both samples a mid-gap minority defect is present albeit its concentration is about one magnitude larger in sulfur-poor samples. These results confirm that sulfur passivates recombination centers in the depletion layer and hence significantly increases the open circuit voltage and the overall device performance of the photovoltaic devices.

Sulfurization of Co-Evaporated Cu(In,Ga)Se2 as a Postdeposition Treatment

“…It has also been shown that an improvement from 14.5% to 16% efficiency can be obtained by annealing with elemental sulfur [6]. Among the explanations for the benefit of surface sulfurization are band gap widening of the surface [5] and passivation of deep defect states [6][7][8]. Annealing CIGSe in the presence of the metalorganic sulfur precursor ditertiarybutylsulfid has also been shown to result in formation of a S/Se surface gradient in coevaporated CIGSe [9].…”

A highly efficient Cu(In,Ga)(S,Se)2 photocathode without a hetero-materials overlayer for solar-hydrogen production

“…On the other hand, the front bandgap grading formed over a depth of about 0 to 200 nm which not only increases CBM but also lowers VBM, preventing surface state recombination by inhibiting photogenerated holes from migrating to electrolyte/CIGSSe interface 26 . In addition, surface sulfurization would passivate mid-gap recombination centers in the space charge region 36,41,42 . We have recently demonstrated that the surface state of CIGSSe can be passivated depending on sulfurization conditions, and thus increase photocurrent density 43 .…”

Temperature dependent current–voltage and admittance spectroscopy on heat-light soaking effects of Cu(In,Ga)Se2 solar cells with ALD-Zn(O,S) and CBD-ZnS(O,OH) buffer layers

“…3(a). The J-V roll-over is an indication of the interface recombination [33,34]. This behavior was suppressed at temperature ranging from 300 K to 220 K after HLS post-treatment ( Fig.…”