Optimization of inkjet printing for copper indium gallium selenide solar absorber thin film

Abstract

The present research is focused on development and optimization of inkjet printing technique to print Copper Indium Gallium Selenide (CIGS) solar cell absorber thin film on rigid substrate. An office inkjet printer is modified to print specific CIG ink on soda lime glass substrate. Metal nitrates are used as precursors and dissolved in a solvent mixture of methanol and ethylene glycol. The ink viscosity, printing process, printing layer and substrate temperature are optimized to print uniform and compact CIGS thin film. The CIG ink viscosity of 3.7 cP and one-time drying approach are chosen to avoid coffee ring, achieve good adhesion, compact and uniform thin film formation. After optimizing of CIG ink viscosity and printing process, the effects of printing layer, and substrate temperatures in the range of 50 ℃ to 80 ℃ are investigated. Thin films are printed with similar crystallinity, compound structures, and elemental composition. The electron scanning micrographs have shown that the surface coverages for 3-layer printed thin films are not as good as 4-layer printed thin films due to deficiency of raw material. The CIGS grains grow freely in 3 dimensions and result in relatively large grain size. Among all 3-layer printed films, the substrate temperature of 70 ℃ has shown thickness of 0.9 µm, better light absorption, relatively large grain size of 797 nm with good surface coverage up to 92%, and surface roughness of 112.4 nm. On increasing the number of printing layer to 4, thin film printed at 70 ℃ shows thickness of 0.8 µm, grain size of 679 nm, good light absorption, 98% surface coverage, and surface roughness of 77.5 nm. Printed CIGS thin films are compared with film deposited by spray coating. The CIGS film deposited by spray coating has shown thickness of 1.5 µm, grain size of 802 nm, poor surface coverage of 78%, worse light absorption, and rough surface condition of 138.1 nm. The comparison between spray and inkjet printing reveals the probability of inkjet printing technique has great potential for deposition of solar thin films.