Surface-treated Cu2ZnSnS4nanoflakes as Pt-free inexpensive and effective counter electrode in DSSC

Inexpensive semiconducting counter electrode (CE) was fabricated from copper zinc tin sulfide (CZTS) nanoflakes (NFs) through simple non-vacuum-based techniques. The kesterite CZTS NFs were synthesized by hot injection method using oleic acid as solvent. CZTS CE was prepared through solid-state ligand exchange method using ammonium sulfide salt ((NH4)(2)S) as the displacement ligand. Thin-film CZTS CE (on FTO substrate) was developed through inexpensive layer-by-layer (LbL) approach, without any post-treatment such as toxic sulfurization process. Hence, the fabrication of CZTS CE through this approach is scalable. The CZTS thin film showed NFs like morphology with higher surface area and achieved good electrocatalytic activity towards the reduction of iodide electrolyte. Two DSSCs using different CEs (CZTS NFs and Pt) were fabricated in separate cell structures in our laboratory. DSSC with CZTS NFs as CE showed the power conversion efficiency of 2.95% which is comparable to the DSSC with Pt (3.11%).