Efficient defect passivation and charge extraction with 2-cyano-5-fluorobenzyl bromide interface modification for hole-transporting layers-free CsPbIXBr3−X perovskite solar cells

Abstract Fully inorganic metal halide perovskite solar cells (PSCs) have become an emerging research hotspot in photovoltaics due to their high efficiency and excellent thermal stability. Unfortunately, HTL-free CsPbI X Br 3−X devices suffer from surface traps on the perovskite films, which severely limits the power conversion efficiency and operational stability of the devices. In this work, we propose a multifunctional passivator, 2-cyano-5-fluorobenzene bromide molecule (2-C-5-FB), to passivate perovskite films by post-treatment, aiming to improve the quality of perovskite films, reduce interfacial defects and non-radiative complexes, enhance carrier separation kinetics, and improve the extraction of carriers, thus improving device performance. The C≡N in the molecular structure immobilizes the undercoordinated Pb 2+ ions, thus passivating the defects in the perovskite films. In addition, the Br atoms on the ring can with the [PbI 6 ] 4− backbone through halogen bonding, and the F atoms form Pb-F and Cs-F, which can effectively reduce the film defects. We prepared passivated devices with the structure of FTO/TiO 2 /CsPbI X Br 3−X /2-C-5-FB/Carbon, and the PCE of the passivated devices was improved compared with the pristine devices, and the cell efficiency was increased from 7.84% to 9.21% with a light intensity of 100 mW cm −2 , and the stability of the devices was also improved. The experimental results indicate that the use of 2-cyano-5-fluorobenzene bromide passivation strategy has a positive effect on the performance enhancement of the perovskite devices, and is an effective way to realize efficient and stable PSCs.