In this letter, MoSe2 nanosheets with flower-like nanostructure was in-situ grown on pre-coated three-dimensional (3D) porous reduced graphene oxide (rGO) thin films on fluorine-doped tin oxide glass by a facile hydrothermal method. The synergistic effect between the highly catalytic MoSe2 nanostructure and the highly conductive and large surface-area 3D rGO network endows the resultant MoSe2/rGO composite excellent electrocatalytic ability. As expected, dye-sensitized solar cells (DSSCs) prepared with MoSe2/rGO thin films as counter electrode (CE) exhibited a conversion efficiency of 6.56%, which was higher than that of DSSCs with sputtered Pt CE (6.08%).

•Cu2ZnSnS4 thin films were prepared directly on FTO substrates by solvothermal method.•The properties and growth mechanism of CZTS thin films were investigated.•Both CTAB and thiourea play a crucial role for formation of different microstructure.•A CZTS thin film solar cells were fabricated and their performance were also studied.In this study, a facile solvothermal method was proposed to grow Cu2ZnSnS4 (CZTS) thin films directly on transparent conductive fluorine-doped tin oxide (FTO) substrates. The hexadecyl trimethyl ammonium Bromide (CTAB) is used as surfactant which is expected to have great effect on the nucleation and growth of the final CZTS thin films on FTO substrate. The effects of CTAB and thiourea concentrations on the crystallographic structure, composition, morphology, optical properties and growth mechanism of CZTS thin films were investigated using scanning electronic microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectrometry (EDS) and UV–visible spectrophotometer, respectively. The solar cells with structure of glass/FTO/CZTS/CdS/i-ZnO/Al–ZnO/Ag were prepared, and the photovoltaic performance of solar cells was studied. The results indicated that Cu2ZnSnS4 thin films are in kesterite phase, composed of a large number of uniform sphere-like particles with an average diameter of about 450–500 nm. Every spherical particle contains many nanocrystals that are 11–12 nm in crystallite size. The concentrations of thiourea or CTAB in precursors do not obviously affect crystal structures, but markedly affect the Cu: Zn: Sn: S atom ratio, surface morphology and microstructure of CZTS thin films. The values of the optical band gap are from 1.37 to 1.54 eV, and the conversion efficiency of CZTS thin film solar cell is 0.16%. It is believed that the similar tetragonal structure and small lattice mismatch between the FTO substrate and Cu2ZnSnS4 both play a key role in promoting the epitaxial nucleation and growth of the Cu2ZnSnS4 thin films on FTO substrates.

•Cu2ZnSnS4 (CZTS) nanospheres thin film was in-situ grown on FTO glass substrate.•The growth temperature does not exceed 200 °C.•CZTS was used as counter electrode without any calcinations treatment.•Low synthesis temperature and low cost make CZTS competitive as counter electrode in DSSCs.A low-temperature solvothermal method was used to in-situ synthesize Cu2ZnSnS4 (CZTS) nanospheres thin film on transparent conductive FTO glass substrates. The CZTS nanospheres were in kesterite-phase, with the diameters of 190–300 nm. The CZTS/FTO was used as counter electrodes (CEs) of dye-sensitized solar cells without any post-treatment. The power conversion efficiency reached up to 1.54%.