Electrical Field-Assisted Direct Ink Deposition of Methylammonium Lead Iodide Layer for Fabricating Large-Scale Inverted Perovskite Solar Cell

A high-performing perovskite solar cell (PSC) requires an outstanding perovskite layer in excellent contact with high-performing charge transfer layers. Commercial development of simple and scalable deposition techniques will need to focus on processes that yield smooth films of uniform composition, microstructure and composition. Ideally, it is desired that the same technique be used sequentially for all of the layers. Several techniques aspire to this goal including one-step chemical solution processes using spin coating and ceramic processing approaches such as doctor-blading, slot-die coating, inkjet printing, and spray coating. As an alternative, we report on the electric field-assisted direct ink deposition (EF-DID) fabrication process for rapid printing of large-area perovskite nanofilms.<br/>Our prior work successfully demonstrated the utility of EF-DID in fabricating PEDOT:PSS hole transport layers. Now we demonstrate its application for depositing perovskite films. Essentially, this technique forms a stable electrospray condition that yields a uniform, large grain-sized perovskite film deposits. Concurrent heat treatment thermally converts the perovskite precursor solution in orthorhombic methylammonium lead iodide (CH₃NH₃PbI₃). Post-deposition, solvent vapor annealing (SVA) refines the films to improve their surface smoothness and to greatly reduce pinhole defects. With very little experimental effort, a ten-fold improvement in the power conversion efficiency (from 1 to 10%) was achieved, suggesting that even greater efficiency can be anticipated in the future.