An unusual charge transfer accelerator of monomolecular Cb-OMe (4,4'-(ortho-carborane)bis(N,N-bis(4-methoxyphenyl)aniline) in perovskite optoelectronic devices

Abstract

Hole transporting layer (HTL) is crucial in the development of high-performance perovskite solar cell (PSC). Here, Cb-OMe (4,4'-(ortho-carborane)bis(N,N-bis(4-methoxyphenyl)aniline) was prepared as a new hole transport material and stacked on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) layer to adjust the energy level and improve the anode interface in inverted PSCs. Cb-OMe had a relatively deep highest occupied molecular orbital (HOMO) energy (-5.18 eV) and high lowest unoccupied molecular orbital (LUMO) energy (-3.12 eV). Its deposition on PEDOT:PSS as bi-HTL (hole transport layer) afforded efficient carrier transport from the perovskite absorber layer to the HTL because of the favorable energy level alignment and enhanced electrical conductivity. Furthermore, since Cb-OMe has a large energy band gap (2.06 eV), high optical transparency was obtained when it is stacked on PEDOT:PSS. Also, the obtained HTL is more hydrophilic, which improved the wettability of the perovskite films. Finally, the devices based on PEDOT:PSS/Cb-OMe showed the enhanced efficiencies compared to the other conditions which were PEDOT:PSS or PEDOT:PSS/4,4'-(Cyclohexane-1,1-diyl)bis(N,N-bis(4-tolyl)aniline) (TAPC)-based devices. As a result, the introduction of Cb-OMe into the cascade structure is an important help in accelerating hole carrier transport. © 2020 Elsevier B.V.