Understanding Nucleation and Film Growth of Perovskite in Confined Volume Printing

Despite the promising characteristics of metal halide perovskites for optoelectronic applications, these materials are highly unstable to environmental factors such as moisture and heat. These instabilities stem predominantly from grain boundary defects, such as halide vacancies that allow more facile ion migration. One strategy to improve the stability of perovskites is to reduce the surface area of the grain boundaries within the film by increasing the grain size. A one-step pathway to increased grain size is limiting nucleation of crystallites followed by rapid growth, resulting in films with fewer, larger crystals. Batch processes have been developed to grow monocrystalline perovskite with confined volumes; however, these processes are slow and not scalable for manufacturing. Conversely, scalable printing techniques such as slot die coating or doctor blading provide limited control over nucleation and growth of crystallites. We have developed a printing process that bridges the gap between scalability and control over crystallization that we call Restricted Area Printing by Ink Drawing (RAPID). RAPID prints films from confined volumes (between a superstrate and substrate) in a continuous process.<br/><br/>Film growth with RAPID can be tuned by controlling the working parameters that dictate the nucleation and growth—confinement gap, residence time, and temperature. We will show the influence of the solvent evaporation rate, distance between substrate/superstrate, and surface chemistry on both the substrate and superstrate on the nucleation and growth of perovskite thin films. Finally, we will demonstrate RAPID-printed perovskite thin films with domains greater than 20 μm and no lead iodide can be achieved in ambient conditions without the need for post processing.