Atomic layer deposition of amorphous antimony sulfide (a-Sb₂S₃) as semiconductor sensitizer in extremely thin absorber solar cell

Atomic layer deposition of amorphous antimony sulfide (a-Sb₂S₃) is demonstrated with an alternating exposure of tris(dimethylamino)antimony (TDMASb) and hydrogen sulfide (H₂S) at 150 °C in a custom-built viscous flow reactor. Growth mechanism and deposition chemistry are investigated by in situ quartz crystal microbalance and in situ Fourier Transform Infrared spectroscopy. Reaction hypothesis facilitating the binary reaction is established by quantum mechanical density functional theory calculations that essentially support the experimental findings. The developed material is used as a photon harvester in solar cells under extremely thin absorber configuration, with TiO₂ and Spiro-OMeTAD as electron and hole transporting layers, respectively. Investigation of charge injection properties with surface photovoltage spectroscopy reveals low but non-negligible density of interfacial (sensitizer/TiO₂) electronic defects. The conventional viscous flow reactor configuration is modified to showerhead-type reactor configuration to achieve better uniformity and conformality of a-Sb₂S₃ on highly porous TiO₂ scaffolds. a-Sb₂S₃ device performance is optimized to achieve the highest power conversion efficiencies of 0.5% while annealed crystalline c-Sb₂S₃ device reaches power conversion efficiencies of 1.9% under 1 sun illumination.