Impact of Interfacial Layers in Perovskite Solar Cells

Perovskite solar cells (PCSs) are composed of organic–inorganic lead halide perovskite as the light harvester. Since the first report on a long‐term‐durable, 9.7 % efficient, solid‐state perovskite solar cell, organic–inorganic halide perovskites have received considerable attention because of their excellent optoelectronic properties. As a result, a power conversion efficiency (PCE) exceeding 22 % was certified. Controlling the grain size, grain boundary, morphology, and defects of the perovskite layer is important for achieving high efficiency. In addition, interfacial engineering is equally or more important to further improve the PCE through better charge collection and a reduction in charge recombination. In this Review, the type of interfacial layers and their impact on photovoltaic performance are investigated for both the normal and the inverted cell architectures. Four different interfaces of fluorine‐doped tin oxide (FTO)/electron‐transport layer (ETL), ETL/perovskite, perovskite/hole‐transport layer (HTL), and HTL/metal are classified, and their roles are investigated. The effects of interfacial engineering with organic or inorganic materials on photovoltaic performance are described in detail. Grain‐boundary engineering is also included because it is related to interfacial engineering and the grain boundary in the perovskite layer plays an important role in charge conduction, recombination, and chargecarrier life time. Upping the face: Interfacial engineering in perovskite solar cells is beneficial to improving photovoltaic performance because of the effective charge collection by changing the work function and/or dipole moment and reducing trapping states and recombination by improving electronic coupling through chemical binding. Bifunctional organic materials or nonstoichiometric approaches are effective methods to passivate grain boundaries of perovskite films.