Detection of binary phases in CuInSe2 films formed by laser annealing of stacked elemental layers of In, Cu and Se

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

“…Replacing the furnace with a laser can reduce this annealing time by 2-3 orders of magnitude. However, previous attempts at laser annealing electrodeposited CISe have not produced material suitable for devices; secondary phases remain [2] and the absorber layers have been observed to melt in the high annealing temperatures [3]. In past work, we have shown that laser annealing coelectrodeposited precursors with a Nd:YAG, continuous wave (CW) laser (λ = 1064 nm) at powers from 50 -1000 Wcm -2 for 0.5 -60 s resulted in CISe absorber layers with evidence of improved crystallinity and optoelectronic properties over the precursor [4].…”

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

“…The difference in final crystallite size between the two methods is explained by localized melting occurring in the free standing films during annealing, where the absence of a substrate prevents thermal conductance away from the film. Bhattacharyya et al 70 extended this approach, keeping the same laser wavelength and dwell times but increasing the precursor thickness to 1.5 μm, which is suitable for photovoltaic devices. 71 Even with an increased film thickness and lower fluxes (<100 W cm −2 ) than in the CW experiments of Laude and Joliet, 68,69 a similar 0.5 to 1 μm grain size was measured in the final absorber.…”

“…This contradicts Laude et al 68 who proposed a near-instantaneous (on the order of 10 −9 s), direct interatomic coupling reaction, facilitated by a liquid In-Se layer over the Se and the nanometer-scale film thickness. The peak temperature in the irradiated SEL precursor was postulated by Laude and modeled by Bhattacharyya to reach between 900°C and 1100°C, 70 which is sufficient to melt the In and Se layers and promote rapid reactions. However, these temperatures also exceed the vaporization temperature of Se, T vap : Se ¼ 685°C, 72 leading to Se loss, and are potentially above the melting temperature of CISe (990°C).…”

“…As outlined above, there are two issues that are hypothesized to limit the progress of this method. First, dewetting of the film 70 leads to a morphology incompatible with substrate configuration thin film solar cells due to direct connection between the front contacts and Mo back contact. Second, the volatility of elemental Se means that it is easily lost from the sample at the calculated laser processing temperatures.…”

“…73 Melted CISe dewets from the Mo substrate forming micrometer droplets. 70 In an effort to further reduce LA time, Walter et al 74 increased the reactivity of their SEL precursors by depositing the precursor as nine layers (i.e., three stacks of Cu/(In or Ga)/Se). This creates a high interfacial potential energy within the precursor and using powers in the range of 1 kW cm −2 , reduced annealing dwell times to tens of milliseconds.…”