The importance of Se partial pressure in the laser annealing of CuInSe<inf>2</inf> electrodeposited precursors

Abstract

One method for producing CuInSe 2 (CISe) absorber layers is electrodeposition followed by annealing. Replacing the commonly used furnace annealing step with a laser can reduce annealing times by 2-3 orders of magnitude: from 30 minutes to 1 s. However, laser processing has, to date, not resulted in absorber layers which can form functioning final devices. One reason is due to Se loss during annealing even on these short timescales. We show how this Se loss is reduced by using a background partial pressure of Se (P Se ) during annealing. Higher P Se results in increased grain size and drastically increased photoluminescence yield. The introduction of an elevated P Se in the laser annealing chamber enabled the fabrication of the first known CuInSe 2 photovoltaic device using electrodeposition followed by laser annealing which gave 1.6% efficiency.

Laser processing for thin film chalcogenide photovoltaics: a review and prospectus

“…85,86,88 A higher Se activity led to an increased Se∕ðCu þ InÞ ratio in the absorber, as well as larger grains and a higher PL yield as compared to lower Se activity. 86 Figure 9(a) illustrates the difference in the PL yield of absorbers annealed under high and low partial pressures of Se. Implementing this new approach, the first and only known working solar cell device to date with a LA absorber was fabricated with a power conversion efficiency of 1.6%.…”

“…Consequently, further work has focused on an "intermediate" time/flux regime. [83][84][85][86] Fluxes between 150 and 945 W cm −2 and a dwell time up to 1 s gave a noticeable structural improvement. This is measurable as an observed increase in grain size between precursor and annealed samples in SEM [see Figs.…”

Cadmium Selective Etching in CdTe Solar Cells Produces Detrimental Narrow-Gap Te in Grain Boundaries

“…Additionally, we show that additive back contact processes such as deposition of Te or ZnTe layers, which to our knowledge are used, at least coincidentally, in all cells to date exhibiting AM1.5 efficiencies above 17%, do not induce such phase changes. Our study is also potentially applicable to other thin-film material applications where chemical etching is used to modify or change the surface chemistry. − …”

Laser processing of materials for renewable energy applications

“…Another team has been using a scanning CW Nd:YAG laser (1064 nm) to anneal electrodeposited CuInSe 2 and has achieved effi ciencies of 1.6%. 73 In other work involving CdTe solar cells, Simonds et al 74 used a KrF excimer laser with 25 ns pulse duration and a wave length of 248 nm to chemically modify the surface of CdTe producing a Te-rich surface that provides an ohmic back contact to the CdTe solar cell.…”