Efficient and ultraviolet durable planar perovskite solar cells: Via a ferrocenecarboxylic acid modified nickel oxide hole transport layer

Planar perovskite solar cells (PSCs) that use nickel oxide (NiO_x) 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_x and the interface contact properties of the NiO_x/perovskite layer are always limited for the NiO_x layer fabricated at a relatively low annealing temperature. Ferrocenedicarboxylic acid (FDA) was firstly introduced to modify a p-type NiO_x 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_x 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_x/perovskite layers and enhancement of the electrical conductivity of the FDA modified NiO_x 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.