Effects of bifunctional metal sulfide interlayers on photovoltaic properties of organic–inorganic hybrid solar cells

Abstract

Bilayer organic–inorganic hybrid solar cells have been fabricated with chemical-bath deposited In₂S₃, SnS, and Sb₂S₃ interlayers between the organic P3HT hole-conducting and inorganic TiO₂ electron-conducting layers. Sb has the highest electronegativity among the elements investigated, and the ionicity of the metal–sulfur bond decreases in the order In₂S₃ (15%) > SnS (9%) > Sb₂S₃ (7%). Thus, with a larger covalent character of the Sb–S bond, Sb may bond to S atoms on P3HT relatively easily compared to In or Sn. Such chemical bonding between Sb₂S₃ and P3HT may then reduce the overall incompatibility between the TiO₂ and P3HT layers, making Sb₂S₃-based devices more efficient compared to In₂S₃- and SnS-based devices. Along with strong photon absorption, the presence of the metal–sulfur bond promotes improved wetting between the TiO₂ sand P3HT layers, resulting in dual functionality for the metal sulfide interlayers. However, along with differences in metal–sulfur bond ionicity, the efficiency improvements seen with Sb₂S₃ can further be attributed to factors like differences in crystal structure, morphology, photon absorption, charge carrier recombination rates, and the manner in which the sulfide layer interacts with TiO₂. While further studies are required to elucidate the exact reason behind the behavior of Sb₂S₃, the findings discussed herein can provide guidelines for identifying novel absorber layers for developing efficient and cost-effective organic–inorganic hybrid photovoltaics.