Impact of selenization with NaCl treatment on the physical properties and solar cell performance of crack-free Cu(In,Ga)Se₂ microcrystal absorbers

In this study, we developed an ink using hexanethiol and Cu(In,Ga)Se-2 microcrystals (CIGSe MCs) to make thin films via doctor blade coating. Besides, crack-free thin films were obtained by optimizing CIGSe MC powder concentration and annealing temperature. Subsequently, single-step selenization was performed with and without sodium chloride (NaCl) surface treatment by carefully tuning the temperature. A crack-free surface with densely packed grains was obtained at 500 degrees C after NaCl treatment. Moreover, the structural parameters of the thin film (annealed at 350 degrees C) were significantly modified via selenization with NaCl at 500 degrees C. For instance, the FWHM of the prominent (112) plane reduced from 1.44 degrees to 0.47 degrees, the dislocation density minimized from 13.10 to 1.40 x 10(15) lines per m(2), and the microstrain decreased from 4.14 to 1.35 x 10(-3). Remarkably, these thin films exhibited a high mobility of 26.7 cm(2) V-1 s(-1) and a low resistivity of 0.03 Omega cm. As a proof of concept, solar cells were engineered with a device structure of SLG/Mo/CIGSe/CdS/i-ZnO/Al-ZnO/Ag, wherein a power conversion efficiency (PCE) of 5.74% was achieved with exceptional reproducibility. Consequently, the outcomes of this investigation revealed the impact of selenization temperature and NaCl treatment on the physical properties and PCE of hexanethiol-based crack-free CIGSe MC ink-coated absorbers, providing new insights into the groundwork of cost-effective solar cells.