The experimental work proceeded in two main packages. The first package consisted of the development of the fabrication procedure of thin films (TF) of the antimony (Sb) and bismuth (Bi) sulphides and their alloys with different Sb:Bi ratios by the closed-space sublimation (CSS) technique with a focus on finding the optimal deposition parameters (1) to produce thin films (TF) of materials with the required physical-chemical and optoelectronic properties; (2) to maintain the fabrication technology energy-saving and scalable. To narrow down the experimental deposition conditions we performed thermodynamic calculations. Several parameters have been monitored to assess the quality of TFs, namely (i) morphology was characterised by SEM, (ii) structure was revealed by XRD, and (iii) basic optoelectronic properties like the optical bandgap, electrical conductivity&charge carrier concentration, and the work function were obtained by UV-Vis, Hall, and Kelvin probe, respectively.
Further advanced optoelectronic characterisation of (Sb/Bi)2S3 TF was performed by energy-resolved electrochemical impedance spectroscopy (ER-EIS) to obtain the experimental electronic density of states (DOS). DOS fitting was performed to identify the materials’ fundamental characteristics, i.e. the valence band maximum (VBM) and conduction band minimum (CBM). The defect identification procedure involved performing DOS calculation by the DFT method and comparing DFT DOS with the experimental one. Noteworthy, the narrowing down of the variety of defects to model was achieved by using a defect formation energy vs work function diagram.
The second experimental work package focused on solar cell (SC) device fabrication and characterisation. In this regard, different SCs buffers (CdS, TiO2, ZnO, SnO2) were tested in the devices with the structure glass/FTO/buffer/passivating layer/absorber/gold contact. To evaluate the best-performing device structure IV characterisation was applied.
