Post-Deposition Sulfur Incorporation into CuInSe₂ Thin Films

Abstract

The effect of initial film composition and substrate in the sulfurization of CuInSe 2 was investigated. CuInSe 2 films deposited on either soda-lime glass (SL) or Corning 7059 ® borosilicate glass (7059) substrates were reacted in flowing H 2 S for times from 1 to 8 hours. Films with Cu-rich composition, Cu/In > 1, reacted for 1 hour had nearly all the Se replaced by S. For Cu-poor films the incorporation of S was significantly reduced. In addition, in Cu-poor films on SL glass CuInS 2 and NaInS 2 were found at the film surface. These phases were not detected in films on 7059 substrates or in Cu-rich films. A phenomenological model is proposed to explain the formation of segregated surface phases in Cu-poor films on SL substrates.

Effect of Cu Content on Post‐Sulfurization of Cu(In,Ga)Se2 Films and Corresponding Solar Cell Performance

“…This confirms that at least the top 200 nm are fully sulfurized. The results emphasize a possibly catalyzing effect of Cu 2− x Se for sulfurization (Cu 2− x Se → Cu 2− x S → CuInS 2 ) as suggested and experimentally proposed earlier …”

“…In addition to the described S–Se exchange mechanisms, Na–In–S plates (presumably NaInS 2 as suggested in a previous study or In 2 S 3 :Na) were locally observed on the absorber surface after sulfurization (see Figure S2, Supporting Information). The same plates were found in the previous study, but no inclusion of Na was reported.…”

Microstructural Characterization of Sulfurization Effects in Cu(In,Ga)Se2 Thin Film Solar Cells

“…The diffusion of sulfur in GBs of CIGSe has been discussed in the literature, due to the clear correlation between the sulfur incorporation and the grain sizes of the absorber layer, where higher sulfur content was detected in microstructures with finer grains (Nakada et al, 1997; Basol et al, 2000; Probst et al, 2001; Titus et al, 2001). The broad spread of the sulfur profile observed here across the GB (see Fig.…”

“…The degradation of the device performance is suggested to be related with the formation of a barrier for the current collection through the growth of a fully converted sulfide layer (Singh et al, 2006). The sulfur incorporation is dependent on the composition (specifically the Cu and Ga concentrations) as well as the mean grain size in the absorber layer, which can vary according to the fabrication technique and parameters implemented (Titus et al, 2001). CIGSSe can be synthesized by the reaction of metal precursors deposited at elevated temperatures followed by a selenization + sulfurization treatment (Nagoya et al, 2001), or by co-evaporation/co-sputtering using physical vapor deposition techniques (Kobayashi et al, 2015).…”

Comparison of Sulfur Incorporation into CuInSe2 and CuGaSe2 Thin‐Film Solar Absorbers

“…For CuInSe 2 (CISe), it has been shown that sulfur diffusion is faster in Cu‐rich compared with Cu‐poor samples. [ 19,20 ] A likely explanation is the rapid transformation of Cu 2 − x Se precipitates within Cu‐rich samples into Cu 2 − x (S,Se), which then act as channels that accelerate sulfur in‐diffusion and promote transformation of the absorber into a CuIn(S,Se) 2 alloy. [ 21 ]…”