Planar perovskite solar cells (PSCs) that use nickel oxide (NiO) as a hole transport layer have recently attracted tremendous attention because of their excellent photovoltaic efficiencies and simple fabrication. However, the electrical conductivity of NiO and the interface contact properties of the NiO/perovskite layer are always limited for the NiO layer fabricated at a relatively low annealing temperature. Ferrocenedicarboxylic acid (FDA) was firstly introduced to modify a p-type NiO hole transport layer in PSCs, which obviously improves the crystallization of the perovskite layer and hole transport and collection abilities and reduces carrier recombination. PSCs with a FDA modified NiO layer reached a PCE of 18.20%, which is much higher than the PCE (15.13%) of reference PSCs. Furthermore, PSCs with a FDA interfacial modification layer show better UV durability and a hysteresis-free effect and still maintain the original PCE value of 49.8%after being exposed to UV for 24 h. The enhanced performance of the PSCs is attributed to better crystallization of the perovskite layer, the passivation effect of FDA, superior interface contact at the NiO/perovskite layers and enhancement of the electrical conductivity of the FDA modified NiO layer. In addition, PSCs with FDA inserted at the interface of the perovskite/PCBM layers can also improve the PCE to 16.62%, indicating that FDA have dual functions to modify p-type and n-type carrier transporting layers.

Hole transport layer NiOx-based inverted perovskite solar cells (PSCs) have advantages of simple fabrication, low temperature, and low cost. Furthermore, the p-type NiOx material compared to that of typical n-type SnOx for PSCs has better photostability potential due to its lower photocatalytic ability. However, the NiOx layer modified by some typical materials show relatively simple functions, which limit the synthesized performance of NiOx-based inverted PSCs. Phenethyl ammonium iodide (PEAI) was introduced to modify the NiOx/perovskite interface, which can synchronously contribute to better crystallinity and stability of the perovskite layer, passivating interface defects, formed quasi-two-dimensional PEA2PbI4 perovskite layers, and superior interface contact properties. The PCEs of PSCs with the PEAI-modified NiOx/perovskite interface was obviously increased from 20.31 from 16.54% compared to that of the reference PSCs. The PSCs with PEAI modification remained 75 and 72% of the original PCE values aging for 10 h at 85 °C and 65 days in a relative humidity of 15%, which are superior to the original PCE values (47 and 51%, respectively) for the reference PSCs. Therefore, PSCs with the PEAI-modified NiOx/perovskite interface show higher PCEs and better thermal stability and moisture resistance.

High performance and stable perovskite solar cells have been fabricated by utilizing thiophene-based interlayers to reduce the energy loss at the SnO2/MAPbI3 interface.

Perovskite solar cells have shown great potential in commercial applicationsdue to their high performance and easy fabrication. However, the electron transport layer (ETL) materials with good optoelectrical properties and energy levels matching that of the perovskite layer still need to be explored to meet the need of commercialization. In this work, 2D Nb 2 CT x MXene nanosheets are prepared and their work function (WF) is reduced from 4.65 to 4.32 eV to match the conduction band minimum of perovskite layer by replacing the surface -F groups with NH 2 groups through hydrazine (N 2 H 4 ) treatment. Besides, the N 2 H 4 treated (T-Nb 2 CT x ) MXene nanosheets with abundant NH 2 groups are incorporated into the perovskite precursor to retard the crystallization rate by forming hydrogen bond with iodine ions, which promotes the formation of high-quality and oriented growth perovskite films. Consequently, the PVSCs with T-Nb 2 CT x MXene ETLs and T-Nb 2 CT x MXene nanosheets additive exhibit the highest power conversion efficiency (PCE) of 21.79% and the corresponding flexible and large-area devices achieve the highest PCE of 19.15% and 18.31%. Meanwhile, the unencapsulated devices maintain 93% of the original PCEs after 1500 h of storage. This work demonstrates the considerable application prospects of 2D Nb 2 CT x MXene in photoelectric devices.