Interface modification for high performance and stable perovskite solar cells

Abstract

Perovskite solar cells (PSCs) have sparked widespread interest as revolutionary semiconductors because of their exclusive photoelectric features and have recently reached a validated power conversion efficiency (PCE) of up to 25.5%, rivaling conventional polycrystalline silicon sun cells. Despite this accomplishment, long-term stability remains a significant barrier to the commercialization of this promising technology. The unremitting effort is significant to make devices more stable with a high performance of PSCs. The interface between perovskite and carrier transport layers (CTLs) plays a critical role in the performance and stability of PSCs. It is critical for the buried interface to impact not just the crystallization of perovskites and non-radiative recombination losses, but also the induced deterioration of the perovskite active layer. For the top interface, it is also considered because high concentrations of defects existed at the interface and the damage of perovskite is normally initialized at surfaces under external stimuli conditions. As a result, appropriate bottom and top interface modification strategies for tailoring interface defects and stability are essential. Firstly, we put forward a triple passivation strategy focusing on two in-between surfaces of nickel oxide (NiOx) hole transport layer (HTL) and methylammonium lead iodide (MAPbI3) perovskite in inverted PSCs. The inorganic salt of potassium thiocyanate (KSCN) is adopted to couple nickel oxide and perovskite layer, improving both device performances and stability significantly. Finally, PSCs with a KSCN interface layer achieves a high PCE of 21.23%, a 1.14 V open-circuit voltage, and better operational stability. These triple interface passivation effects help the development of potential multiple passivation techniques for optimizing PSC performance and stability. Secondly, we proposed the imidazole bromide functionalized graphene quantum dots (I-GQDs) to tailor the interface between tin oxide (SnO2) electron transport layer (ETL) and formamidinium lead iodide (FAPbI3) perovskite layer in regular planar PSCs. I-GQDs possess high conductivity, which can enhance charge transfer at the interface. Additionally, the imidazole bromide functional groups can passivate the interface defects, resulting in reduced non-radiative recombination. Moreover, the use of I-GQDs not only optimizes the interface energy level alignment, but also improves perovskite quality, decreasing trap density, and increasing carrier lifespan. As a consequence, FAPbI3-based PSCs with I-GQDs interface layer achieves a high efficiency of 22.37% while improving long-term stability. Finally, we develop a solid-solid contact (SSC) passivation strategy to build up a multifunctional Nafion and EDTMP ion lock interface layer between perovskite and top organic HTL, interacting strongly with the perovskite. The Nafion and EDTMP ion lock layers not only significantly reduce interface defects but also fine-tune the work function of perovskite, resulting in enhanced carrier extraction and increased build-in electric field. Moreover, the Nafion and EDTMP ion lock interface layer can successfully lock the metal cations and ammonium salt anions at the interface to enhance the stability of the devices. Eventually, the perovskite solar cells with multifunctional Nafion and EDTMP ion lock layer deliver a high PCE with desirable light and long-term operational. Our findings offer guidelines for developing defect-minimizing interfaces between metal halide perovskites and hole-transporting layers.