An alternative chlorine-assisted optimization of CdS/Sb2Se3 solar cells: Towards understanding of chlorine incorporation mechanism

The current strategies in the development of Sb 2 Se 3 thin film solar cells involve fabrication and optimization of superstrate and substrate device architectures, with the preferable choice for TiO 2 and CdS heterojunction layers. For CdS-based superstrate cells, several studies reported the necessity to apply CdCl 2 or other metal halide-based post-deposition treatment (PDT), highlighting improvement of CdS/Sb 2 Se 3 device efficiency. However, the need, effect, and mechanism of such PDT are very often not described. Additionally, the fact that many groups have not succeeded in demonstrating its benefits suggests that this strategy is not straightforward, requiring a deeper understanding towards a more unified concept. The present study proposes an alternative approach to the challenging CdCl 2 PDT of CdS in CdS/Sb 2 Se 3 device, involving controllable Cl incorporation in CdS films by systematically varying the concentration of NH 4 Cl in the CBD precursor solution from 1 to 8 mM. Structural and electrical characterizations are correlated with advanced measurements of Scanning Kelvin Probe, surface photovoltage, and atomic force microscopy to understand the impact of Cl incorporation on the properties of CdS films and CdS/Sb 2 Se 3 devices. The validity of Cl incorporation in the CdS lattice and interdiffusion processes at the CdS-Sb 2 Se 3 interface is confirmed by secondary ion mass spectrometry analysis. It is demonstrated that incorporation of 1 mM of NH 4 Cl, as a Cl source in CBD CdS, can boost the PCE of CdS/Sb 2 Se 3 by ∼20 %. With this approach, we offer new perspectives on the optimization methodology for Cl-based CdS/Sb 2 Se 3 device processing and complementary understanding of the physiochemistry behind these processes. • Controllable chlorine-assisted optimisation of CdS/Sb2Se3 solar cells. • 20 % boost in performance through chlorine-assisted processing. • SIMS analysis demonstrating Cl incorporation and interface interdiffusion. • Interrelation between Cl incorporation mechanism and device performance provided.