Interface engineering approaches for efficient and robust perovskite solar cells

The field of perovskite photovoltaics has been witnessing a surge of interest over the past few years across the breadth of advanced nanomaterials, nanoscience and nanotechnology. Of particular interest, controlling the nanomorphology of the hybrid perovskite absorber can modify intrinsically different properties (crystallinity, defects, grain boundaries) and optimize charge transport in the bulk structures and at the corresponding interfaces, thus leading to devices with high power conversion efficiency and enhanced stability. The perovskite absorber and its interfaces with the electron transport layer (ETL) and the hole transporting material (HTM) play a pivotal role in obtaining perovskite solar cells (PSCs) with high power conversion efficiency (PCE) and enhanced stability. This contribution deals with advanced engineering strategies developed by our group focusing on the ETL/perovskite and perovskite/HTL interfaces optimization to regulate the geometric, structural and electronic properties of the solar cell basic components. The energy level alignment at the interfaces of the perovskite solar cells is an essential factor that determines their efficiency and stability. Therefore, an interface capable of appropriate energy band bending, minimal defects and good contacts is the key issue to obtain highly performing and stable PSCs. Both inorganic and organic interlayers have used to adjust the energy levels of perovskite. Improved crystallization is at the origin of increased short circuit photocurrent (Jsc). The improvement of open circuit potential (Voc) and fill factor (FF) can be attributed to the effective perovskite passivation. The addition of interlayers influences the activation energy growth and reduces the crystallization rate, leading to larger perovskite grains with less defects and higher crystallinity. As a result the interfacial carriers (electrons and holes) extraction was enhanced, the nonradiative carrier recombination was suppressed and the power conversion efficiency was increased. Furthermore, the modified interfaces are endowed with an ultra-hydrophobic character, protecting the perovskite from moisture while mitigating ionic diffusion and thus leading to excellent device stability. These innovative interface engineering approaches provide important guidance for the development of functional interlayers that lead to efficient and robust perovskite solar cells.