Passivation of perovskite layer surface states with pyridine in flexible and printed perovskite solar cells

Perovskite solar cells (PSCs), prepared by using solution-processed printing techniques, gained much attention over the past few years and a considerable progress has been achieved in improving the power conversion efficiencies of these devices. Nevertheless, there are still some advancements that can be implemented, especially in terms of passivation of surface defects in the perovskite photoactive layer. Passivation can afford considerable reduction in surface recombination of charge carriers in the photoactive layer and help to obtain devices with better performance. In this work, poly(3-hexylthiophene-2,5-diyl)-based inks with small amount of pyridine as an additive are used to deposit the hole transport layer and simultaneously passivate the surface defects of the perovskite layer in flexible and printed PSCs. The devices are fabricated on flexible conductive plastic substrates using a slot-die coating method. It is found that 2.5 wt.% pyridine-containing inks for preparing hole transport layer have a positive effect on the performance of resulting PSCs. On average, around 13% improvement in the power conversion efficiency is observed for the devices with passivation as opposed to the reference devices without passivation. The effect of pyridine passivation on the structural and electronic properties of the perovskite layer on a flexible substrate is studied using experimental and analytical techniques, whereas the computer simulation methods are employed to rule out the possible mechanisms for the performance improvements in the devices with passivation. The approach presented here can be useful for developing simplified protocols for printing of flexible PSCs with the passivated perovskite layer and improved device efficiency.