Naphthobischalcogenadiazole Conjugated Polymers: Emerging Materials for Organic Electronics

Abstract

Semiconducting polymers can function as both p-type (hole-transporting) and n-type (electron-transporting) materials in those devices. [17][18][19] In OFETs, holes and electrons are injected into the semiconducting polymer at the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively. [10] Those charge carriers are then transported between the source and drain electrodes through the assembled polymer backbones. [20,21] In OPVs, [22] the semiconducting polymer absorbs the sunlight within the polymer absorption range (or the sunlight energy above the polymer bandgap (E g )), generating excitons where the hole and electron are strongly bounded. These excitons then diffuse into the interface of the p-type semiconducting polymer and the n-type material (typically methanofullerenes, [23] but can also be n-type semiconducting polymers [24] or small molecules [25] ), at which the excitons dissociate into free holes and electrons. [23,26,27] Those charge carriers are then transported to the electrodes through the materials domains. Therefore, regardless of the device types, the electronic properties and the charge transport properties are the most important characteristics of the polymers.With respect to the electronic structure, E g and HOMO and LUMO energy levels (E HOMO and E LUMO ) are important parameters for semiconducting polymers. [28] As E g qualitatively indicates the extent of π-electron delocalization along the conjugated backbone, a narrow E g is supposed to be preferable for charge transport, especially along the backbone. E g is more important for OPVs, i.e., a narrow E g is highly desired in order to maximize sunlight harvesting. Deep E HOMO , which refers to large ionization potential (IP), is essential for the p-type semiconducting polymer. This provides oxidative stability of the material [29] as well as higher open-circuit voltage (V OC ) in OPVs that is proportional to the energy difference between the HOMO of the p-type material and LUMO of the n-type material. [30] On the other hand, deep E LUMO , which refers to large electron affinity (EA), is essential for the n-type semiconducting polymer since this offers stable electron transport in ambient conditions. [31] The E LUMO is also important for p-type semiconducting polymers when they are used in OPVs. As narrow E g and deep E HOMO are required for p-type semiconducting poly mers in OPVs, their E LUMO must be deepened. It should be noted, however, the E LUMO of the p-type semiconducting π-Conjugated polymers are an important class of materials for organic electronics. In the past decade, numerous polymers with donor-acceptor molecular structures have been developed and used as the active materials for organic devices, such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). The choice of the building unit is the primary step for designing the polymers. Benzochalcogenadiazoles (BXzs) are one of the most familiar acceptor building units studied in this area. As their doubl...

Eco‐Compatible Solvent‐Processed Organic Photovoltaic Cells with Over 16% Efficiency

“…[4][5][6] Benefiting from the great efforts devoted to the design of new materials, [7][8][9][10][11][12][13] optimization of the blend morphology, [14][15][16][17][18] understanding the charge generation mechanism, [19][20][21][22][23][24][25][26] significant progress has been achieved in the last few years. [4][5][6] Benefiting from the great efforts devoted to the design of new materials, [7][8][9][10][11][12][13] optimization of the blend morphology, [14][15][16][17][18] understanding the charge generation mechanism, [19][20][21][22][23][24][25][26] significant progress has been achieved in the last few years.…”

Influence of Backbone Chlorination on the Electronic Properties of Diketopyrrolopyrrole (DPP)‐Based Dimers

“…This approach has been proved to be an effective strategy to tune the thin film morphology, which strongly influences the charge separation and charge transport. On the other hand, the material properties can be also tuned via modification the π‐conjugated backbone that has great impact on the electronic structure, such as ionization potential, electron affinity, and electronic delocalization . In recent years, different strategies have been developed to a fine‐tuning energy level through the careful combinations of different subunits or the incorporation of electron‐donating/electron‐withdrawing substituents into backbones .…”

“…On the other hand, the material properties can be also tuned via modification the p-conjugated backbone that has great impact on the electronic structure, such as ionization potential, electron affinity,a nd elec-tronic delocalization. [17][18][19][20][21][22] In recenty ears, different strategies have been developed to af ine-tuning energy level through the careful combinationsofdifferent subunits or the incorporation of electron-donating/electron-withdrawings ubstituents into backbones. [23][24][25][26][27] For example, fluorine atom has been widely incorporated into polymer backbones that significantly influence the energy level, backbonep lanarity,s olubility,a nd crystallization.…”

Effects of alkyl side chain length of low bandgap naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole‐based copolymers on the optoelectronic properties of polymer solar cells

“…Besides the aforementioned considerations, coplanar geometries and rigid structures can effectively suppress the rotational disorder around the interannular single bond and lower the reorganization energy, resulting in an enhanced intrinsic charge mobility . Among the various A units, naphtho[1,2‐ c :5,6‐ c ′]bis[1,2,5]thiadiazole (NT) bearing an enlarged planarity and a stronger electron‐withdrawing feature exhibited the interesting electronic properties and highly self‐assembling nature . And thus, these NT‐based CPs have attracted the increasing attention .…”