Perovskite/Hole Transport Layer Interface Improvement by Solvent Engineering of Spiro-OMeTAD Precursor Solution

Perovskite solar cells (PSCs) are one of the most promising emerging energy-conversion technologies because of their high power conversion efficiencies (PCEs) and potentially low fabrication cost. To improve PCE, it is necessary to develop PSCs with good interfacial engineering to reduce the trap states and carrier transport barriers present at the various interfaces of the PSCs' architecture. This work reports a facile method to improve the interface between the perovskite absorber layer and the hole transport layer (HTL) by adding a small amount of acetonitrile (ACN) in the Spiro-OMeTAD precursor solution. This small amount of ACN dissolves the surface of the perovskite layer, allowing the formation of an interdiffusion structure between perovskite and Spiro-OMeTAD layers. This modification allows for an improved electrical contact, enhanced collection of holes, and reduced recombination losses at the interface between the perovskite and Spiro-OMeTAD layers and, consequently, enhances the PCE. A maximum PCE of 19.7% with low hysteresis and a steady-state power conversion efficiency of 19.0% is obtained for optimized PSCs.