Zn(O,S) Buffer Layer for in Situ Hydrothermal SbS Planar Solar Cells.

Hydrothermal deposition is emerging as a highly potential route for antimony-based solar cells, in which the Sb(S,Se) is typically in situ grown on a common toxic CdS buffer layer. The narrow band gap of CdS causes a considerable absorption in the short-wavelength region and then lowers the current density of the device. Herein, TiO is first evaluated as an alternative Cd-free buffer layer for hydrothermally derived SbS solar cells. But it suffers from a severely inhomogeneous SbS coverage, which is effectively eliminated by inserting a Zn(O,S) layer. The surface atom of sulfur in Zn(O,S) uniquely provides a chemical bridge to enable the quasi-epitaxial deposition of SbS thin film, confirming by both morphology and binding energy analysis using DFT. Then the results of the first-principles calculations also show that Zn(O,S)/SbS has a more stable structure than TiO/SbS. The resultant perfect Zn(O,S)/SbS junction, with a suitable band alignment and excellent interface contact, delivers a remarkably enhanced and for SbS solar cells. The device efficiency with the TiO/Zn(O,S) buffer layer boosts from 0.54% to 3.70% compared with the counterpart of TiO, which has a champion efficiency of Cd-free SbS solar cells with a structure of ITO/TiO/Zn(O,S)/SbS/Carbon/Ag by in situ hydrothermal deposition. This work provides a guideline for the hydrothermal deposition of antimony-based films upon a nontoxic buffer layer.