Sb₂S₃ Thickness-Related Photocurrent and Optoelectronic Processes in TiO₂/Sb₂S₃/P3HT Planar Hybrid Solar Cells

In this work, a comprehensive understanding of the relationship of photon absorption, internal electrical field, transport path, and relative kinetics on Sb₂S₃ photovoltaic performance has been investigated. The n-i-p planar structure for TiO₂/Sb₂S₃/P3HT heterojunction hybrid solar cells was conducted, and the photon-to-electron processes including illumination depth, internal electric field, drift velocity and kinetic energy of charges, photo-generated electrons and hole concentration-related surface potential in Sb₂S₃, charge transport time, and interfacial charge recombination lifetime were studied to reveal the key factors that governed the device photocurrent. Dark J–V curves, Kelvin probe force microscope, and intensity-modulated photocurrent/photovoltage dynamics indicate that internal electric field is the main factors that affect the photocurrent when the Sb₂S₃ thickness is less than the hole diffusion length. However, when the Sb₂S₃ thickness is larger than the hole diffusion length, the inferior area in Sb₂S₃ for holes that cannot be diffused to P3HT would become a dominant factor affecting the photocurrent. The inferior area in Sb₂S₃ layer for hole collection could also affect the V_oc of the device. The reduced collection of holes in P3HT, when the Sb₂S₃ thickness is larger than the hole diffusion length, would increase the difference between the quasi-Fermi levels of electrons and holes for a lower V_oc.