Cu2ZnSnS4 prepared sulfurizing a stack of electrodeposited metallic layers

GONZALO PERELSTEIN; ANTONIO DA CUNHA; MATIAS VALDES; MARCELA VAZQUEZ

Simposio; 7th Regional Symposium on Electrochemistry for South-East Europe RSE SEE7.; 2019

Cu2ZnSnS4 (CZTS) is an extensively studied kesterite that can be used as absorber layer in inorganic solar cells. A direct bandgap energy value (EGAP) close to 1.5 eV and a high absorption coefficient make it a suitable material for this purpose [1]. Furthermore, compared to competing family compounds such as chalcopyrites (CuInGaSe2), it has the advantage of including ?green?, inexpensive and abundant elements. CZTS films are thus excellent candidates for low-cost, highly efficient and environmentally friendly thin-film solar cells [2].There are numerous electrochemical routes to deposit CZTS. In a previous work [3] we explored the so-called ?one-pot? electrodeposition but we found it difficult to stabilize the sulfur source in the precursor mixture. Later [4], we explored with the co-electrodeposition of a Cu-Zn-Sn precursor (CZT) from a ternary precursor bath, followed by a sulfurization stage that transforms the precursor into CZTS. This work describes the consecutive electrodeposition of metallic thin films (Cu, Sn and Zn) on conductive glass, which transforms in CZTS after the sulfurization treatment. The thickness of each metallic layer was calculated by coulometry and ranged between 200 and 320 nm. The Cu-Sn-Zn stack was first annealed at 350 °C during 30 min and later underwent reactive sulfurization at either 500 or 585 °C for 10 min. The vaporized sulfur reached the samples assisted by N2 flux. CZTS films were characterized by Raman spectroscopy, scanning electronic microscopy (SEM), and UV-Vis spectroscopy. SEM results showed good coverage and homogenous morphology. Raman spectroscopy confirmed the formation of crystalline CZTS after sulfurization, with no secondary phases detected in the film. The bands are sharp and clear particularly for those samples annealed at 585 °C. Direct energy gap values close to 1.5 eV were estimated for CZTS films by UV-Vis spectroscopy. CZTS films are good-quality absorbers suitable to be used in kesterite thin films solar cells. The same procedure has been tested using Mo-coated glass as substrates, so that different arquitectures (substrate and superstrate solar cells) can be chosen using this deposition methodology.