Investigation on in-situ thermal treatment of room-temperature pulsed laser deposition technique: How to improve Cu2ZnSnS4 films for photoelectric application without sulfurization

Abstract

Is extra sulfurization an indispensable process for synthesizing quaternary chalcogenide? The answer is probably affirmative for most synthesismethods to suppress excessive sulfur vacancies. Pulsed laser deposition (PLD), an acknowledged technique for fabricating films with complex stoichiometry, is a greatalternative approach to prepare Cu2ZnSnS4 (CZTS) films. However, to prevent evaporative losses the deposition temperature (Tis) must be limited below 400 °C, which makes post-annealing process extremely requisite to improve metastable films. Herein we develop an in-situ thermal treatment technique in room-temperature (RT)-PLD-synthesis of CZTS films to evade extra sulfurization process. According to multi-peaks Gaussian fitting analysis, RT-PLD implementing optimized in-situ treatment can broaden solar absorption of CZTS films, potentially contributed by sub-bandgap absorption due to intrinsic natural-intermedium-band effects of I2-II-IV-VI4 chalcogenide compounds. Stabilized chronoamperometry characterization combined with quasi-stoichiometric ratio demonstrates that the RT-PLD technique can equivalently restrain sulfur vacancy generation even without sulfurization. Physical mechanisms associated to order–disorder transitions of polycrystal CZTS during in-situ treatment can interpret morphological “lumpy-smooth-vuggy” transformation along with Tis varied. Therefore, such proposed RT-PLD technique is applicable to prepare polynary compounds with volatile elements and complicated stoichiometry ratio.