(Invited) Tailoring Crystal Morphology and Interfacial Charge Transfer in Perovskite Solar Cells

Abstract

The past decade has witnessed tremendous advances in organometal halide perovskite solar cells (PSCs) due largely to the stellar set of optoelectronic properties of perovskites such as high absorption coefficient, long carrier diffusion length, and low electron-hole recombination. Notably, organolead halide PSC has reached a certified champion power conversion efficiency (PCE) of 25.5%. In this talk, first, I will discuss a meniscus-assisted solution printing (MASP) strategy to yield large-grained dense perovskite film with good crystallization and preferred orientation. The growth kinetics of perovskite crystals is scrutinized by in-situ optical microscopy tracking to understand the crystallization mechanism. The perovskite film produced by MASP exhibits excellent optoelectronic properties for high-efficiency PSCs. We also MASP cross-aligned conductive nanowires for biodegradable flexible PSCs. Second, I will present a simple yet robust acid-treatment strategy to judiciously create an amorphous TiO2 buffer layer intimately situated on the anatase TiO2 surface as electron transport layer (ETL) for efficient electron transport. The facile acid treatment is capable of weakening the bonding of zigzag octahedral chains in anatase TiO2, thereby shortening staggered octahedron chains to form an amorphous buffer layer on the anatase TiO2 surface. Such amorphous TiO2-coated ETL possesses an increased electron density due to the presence of oxygen vacancies, leading to efficient electron transfer from perovskite to TiO2. Compared to pristine TiO2-based devices, the perovskite solar cells (PSCs) with acid-treated TiO2 ETL exhibit enhanced short circuit current and PCE. Notably, we also tailor carrier dynamics in PSCs via precise dimension and architecture control and interfacial positioning of plasmonic nanoparticles in TiO2 ETL. Third, I will demonstrate synergistic cascade carrier extraction via dual interfacial positioning of ambipolar black phosphorene (BP) for high-efficiency PSCs. Concurrently enhanced carrier extraction at both electron transport layer/perovskite and perovskite/hole transport layer interfaces is achieved through judicious design and position of BP with tailored thickness as dual-functional nanomaterials. Fourth, I will introduce a robust route that simultaneously allows defect passivation and reduced energy difference between perovskite and hole transport layer (HTL) via the judicious placement of polar chlorine-terminated silane molecules at the interface. An integrated experimental and density functional theory study demonstrates that the dipole layer formed by the silane molecules decreases the perovskite work function, imparting an Ohmic character to the perovskite/HTL contact. The corresponding PSCs manifest a nearly 20% increase in PCE over pristine devices and a markedly enhanced device stability. Finally, I will show the spatial poling-initiated perovskite self-healing for defects passivation. The spatial poling significantly enhances the ion migration recovery after removing electric field. Particularly, the ion recovery tends to form a perfect lattice structure, leading to decreased defects in the perovskite layer with enhanced stability.