A Versatile Buffer Layer for Polymer Solar Cells: Rendering Surface Potential by Regulating Dipole

Abstract

Spin‐coated film of poly(vinylidenefluoride‐hexafluoropropylene) (P(VDF‐HFP)) acts as a cathode/anode buffer layer in polymer solar cells (PSCs) with conventional/inverted device structures. Such devices show optimized performances comparable with the controlled device, making P(VDF‐HFP) a good substitute for LiF/MoO3 as a cathode/anode buffer layer. Ultraviolet photoelectron spectroscopy (UPS) and Kelvin force microscope (KFM) measurements show that increased surface potential of active layers improves cathode contact. In piezoresponse force microscopy (PFM) measurement, P(VDF‐HFP) responds to applied bias in phase curve, showing tunable dipole. This tunable dipole renders surface potential under applied bias. As a result, open‐circuit voltage of devices alters instantly with poling voltage. Moreover, positive poling of P(VDF‐HFP) together with simultaneous oxidation of Ag gradually improves performance of inverted structure device. Integer charge transfer (ICT) model elucidates improved electrode contacts by dipole tuning, varying surface potential and vacuum level shift. Understanding the function of dipole makes P(VDF‐HFP) a promising and versatile buffer layer for PSCs.

Unravelling Work Function Contributions and Their Engineering in 2H-MoS2 Single Crystal Discovered by Molecular Probe Interaction

“…For the samples TT300 and TT500, the downward shift observed for core levels is 0.10 and 0.25 eV (see Table ), which is assumed to be equal to the surface band bending and is partially responsible for the work function increase of each sample. It has already been found that surface defects are one of the principal reasons for surface band bending. , In addition, the formation of a net dipole pointing toward the bulk implies an increase of the sample work function. − Therefore, we attribute the other part of the work function increase (0.10 and 0.23 eV, respectively) to the formation of a surface dipole moment. The simple model in Figure b summarizes the fact that both the formation of a surface dipole and surface band bending contribute to the increase of the work function and hence p-type behavior of thermally treated MoS 2 .…”

A New Function of N719: N719 Based Solution‐Processible Binary Cathode Buffer Layer Enables High‐Efficiency Single‐Junction Polymer Solar Cells

“…Recently, much attention has been paid to water/alcohol soluble polymer and small molecule CBL materials because of their advantages, such as tunability in molecular structure, solution‐processability, easy‐handling, and flexibility. These materials contain special functional groups such as fluorine atom, carboxylic acid, sulfonate, amino, ammonium, and/or amino N‐oxide units, which are covalently linked with aliphatic chains, resulting in ethylenimine derivatives and fluoro‐substituted polymers, or linked with conjugated π‐system, for example, fluorene, perylene diimide (PDI), and fullerene . Interactions between these special functions with the bare electrode surface help to create the interfacial dipole (Δ) so as to increase the vacuum‐level and reduce the work function ( ϕ ) of the metal cathode.…”

Nanoporous nickel with rich adsorbed oxygen for efficient alkaline hydrogen evolution electrocatalysis

“…In comparison, the OCP of the np-Ni electrode is ~0.14 V RHE , which is significantly lower than those of other samples. Taking into account the condition of electrical neutrality, the shift of surface potential is related to the change of surface charge distribution caused by dipoles [31][32][33]. This means that the presence of appropriate atoms with greater electronegativity generates electric dipoles on the np-Ni surface.…”