Study of Energetic Distribution of Traps in Perovskite Solar Cell With Iron Pyrite as a Hole Transport Layer

Hole transport material plays a crucial role in terms of efficiency and long-term stability of organic -inorganic hybrid perovskite solar cells (PSCs). Traditionally, PSCs have been fabricated with the conventional sandwich structure using TiO₂ as the electron transport layer (ETL) and Spiro-OMeTAD as the hole transport layer (HTL). However, the major limitation of spiro-OMeTAD as a HTL is it’s cost and stability. The cost of high purity spiro-OMeTAD (> $170/gram) is ten times more than that of platinum or gold because of complex material synthesis and purification processes. Furthermore, moisture can easily penetrate through the spiro-OMeTAD layer because of its hygroscopic nature and react with underlying perovskite films. This could lead to rapid degradation under humid conditions as perovskite is highly unstable towards polar solvent like water, resulting in the production of toxic lead components. Here, we address both these issues by utilizing chemically synthesized phase pure FeS₂ nanoparticles as earth abundant cost effective moisture-proof HTL for PSCs. We have also investigated their hole extraction, transportation and collection capabilities through transient photo voltage and photocurrent spectroscopy analysis. Transient spectroscopy reveals the energetic distribution of trap states at the perovskite/FeS₂ interfaces. This study provides us an opportunity to investigate energetic distribution of the trap density of states in the devices and correlate with device performances using iron pyrite as a novel HTL.