Molecule‐Doped Nickel Oxide: Verified Charge Transfer and Planar Inverted Mixed Cation Perovskite Solar Cell

TLDR

Conductivity and mobility are essential for charge transfer in perovskite solar cells, yet ionic doping introduces defects that degrade mobility and promote recombination. The study introduces a novel molecular doping of the NiOx hole transport layer using the perfluoronaphthalene dimalononitrile F6TCNNQ. This doping is achieved by incorporating F6TCNNQ into NiOx, and first‑principle calculations together with electrostatic force microscopy confirm direct electron transfer from NiOx to the dopant. XPS and UPS reveal that the NiOx Fermi level shifts from –4.63 to –5.07 eV and the VBM–EF gap narrows from 0.58 to 0.29 eV, reducing the VB offset to 0.04 eV, while the average power‑conversion efficiency of CsFAMA mixed‑cation PSCs rises by ≈8 % to a champion 20.86 % (and 19.75 % for MAPbI3), showing that this molecular doping offers a promising alternative to passivation for inorganic CTLs.

Abstract

Both conductivity and mobility are essential to charge transfer by carrier transport layers (CTLs) in perovskite solar cells (PSCs). The defects derived from generally used ionic doping method lead to the degradation of carrier mobility and parasite recombinations. In this work, a novel molecular doping of NiOx hole transport layer (HTL) is realized successfully by 2,2'-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6TCNNQ). Determined by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy, the Fermi level (EF ) of NiOx HTLs is increased from -4.63 to -5.07 eV and valence band maximum (VBM)-EF declines from 0.58 to 0.29 eV after F6TCNNQ doping. The energy level offset between the VBMs of NiOx and perovskites declines from 0.18 to 0.04 eV. Combining with first-principle calculations, electrostatic force microscopy is applied for the first time to verify direct electron transfer from NiOx to F6TCNNQ. The average power conversion efficiency of CsFAMA mixed cation PSCs is boosted by ≈8% depending on F6TCNNQ-doped NiOx HTLs. Strikingly, the champion cell conversion efficiency of CsFAMA mixed cations and MAPbI3 -based devices gets to 20.86% and 19.75%, respectively. Different from passivation effect, the results offer an extremely promising molecular doping method for inorganic CTLs in PSCs. This methodology definitely paves a novel way to modulate the doping in hybrid electronics more than perovskite and organic solar cells.