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 Voc 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 Voc.
Keywords: Optoelectronic processes; Photocurrent; Sb2S3; Solar cells.