H. J. Meadows, A. Bhatia, V. Depredurand, J. Guillot, D. Regesch, A. Malyeyev, D. Colombara, M. A. Scarpulla, S. Siebentritt, and P. J. Dale
The Journal of Physical Chemistry C, vol. 13, no. 3, pp. 219-222, 2014
<aside><aside>Cu(In,Ga)Se<sub>2</sub> (CIGSe) is a polycrystalline absorber layer in thin film solar cells with solar conversion efficiencies exceeding 20%. High temperature annealing for periods of minutes to hours is currently required to convert amorphous or nanocrystalline precursor material into high quality Cu(In,Ga)Se<sub>2</sub> absorber layers. In this work, we perform the critical annealing step, using a 1064 nm laser, on electrodeposited precursor layers containing Cu, In, and Se, for times of 0.3-60 s thus synthesizing CuInSe <sub>2</sub> absorber layers. An annealing time of 1 s is found to be sufficient to remove elemental concentration gradients in the bulk of the layer and to increase the average implied crystallite size (crystal coherence length, as determined by X-ray diffraction, XRD). Therefore the rate-determining step in producing higher quality layers with short annealing times is the rate of grain growth and not atomic diffusion. Optoelectronic analysis of the absorber layers revealed p-type doping with improved radiative recombination compared to the precursors. Laser annealed CuInSe<sub>2</sub> layers did not produce working photovoltaic devices. This is first attributed to a loss of Se that occurs during laser annealing, resulting in detrimental substoichiometric quantities of Se in the absorber. Second, the likely presence of a thick surface layer of the CuIn<sub>3</sub>Se<sub>5</sub> phase is expected to detrimentally impact device performance. These findings must be addressed if annealing times of the CuInSe<sub>2</sub> absorber layer are to be reduced to seconds. © 2013 American Chemical Society</aside></aside>