Multichannel Strategies to Produce Stabilized Azaphenalene Diradicals: A Predictable Model to Generate Self‐Doped Cathode Interfacial Layers for Organic Photovoltaics

Abstract

Self‐doped cathode interfacial layers (CILs) are crucial to enable Ohmic‐like contact between the electrode and organic functional layers and thus profoundly promote the performances of organic optoelectronic devices. Herein, multifarious azaphenalene‐embedded organic salts with variable counterions, substituent groups, and repeating units are prepared, and their impacts on producing homologous diradicals are established. Electron paramagnetic resonance and X‐ray photoelectron spectroscopy studies reveal the existence of free radicals of these azaphenalene salts in the solid state. Density functional theory simulations indicate that the thermal energy of counterion‐induced proton transfer is crucial to produce diradicaloids, which can be manipulated in tailoring the azaphenalene backbones. Noticeably, the formed diradicaloids that are delocalized over the π‐conjugated systems will be beneficial to enhance the carrier density of the matrix and remarkably decrease the work functions of the Al electrode. The all‐solution‐processed bulk heterojunction organic solar cells are fabricated by employing them as CILs, which results in high power conversion efficiency of 10.24% in contrast to the 7.34% of the reference device without CILs.

Significantly Reduced Thermal-Activation Energy for Hole Transport via Simple Donor Engineering: Understanding the Role of Molecular Parameters for Thermoelectric Behaviors

“…To realize a high PF of the OTMs, feasible strategies involving a valid approach to sharpen the local increase of density of states (DOS) nearby the Fermi level ( E F ) of the materials deliver a predictable means to modify their S . − Alternatively, an ion accumulation mechanism with the incorporation of ionic liquid at the surface enables another channel to increase the S of the samples . On the other hand, molecular design with the concept of low effective masses of charge carriers (that is, an intrinsic high mobility) renders an effective way to screen out satisfactory OTMs with high σ. − Besides, side chain engineering by introducing large polarity oxyalkyl chains provides additional technique to facilitate the coprocessing of dopant/polymer pairs, which is beneficial to improving the molecular arrangement for σ-enhancement. , Nevertheless, chemical doping is the essential requirement for OTMs due to the intrinsic low σ, − and therefore endeavors to clarify the differences of doping behaviors of the OTMs on account of the variation of molecular parameters are more significant. − Here, the electrical properties of the doped organic semiconductors are mainly dominated by the thermal activation energy of conductivity ( E act ,σ ) which can be inferred from the Coulomb binding energy ( E coul,ICTC ) or static energy disorder (σ ICTC ) of the integer charge transfer complexes (ICTCs) at low or high doping concentrations, respectively . On this score, subsequent efforts to decrease the E act ,σ values of the materials from the perspective of molecular parametric manipulation is of vital importance, which affords the key variable for thermoelectric properties optimization.…”

Control of Nanomorphology in Fullerene-Free Organic Solar Cells by Lewis Acid Doping with Enhanced Photovoltaic Efficiency

“…Charge-transfer doping with molecular dopants has been successfully applied for organic optoelectrical devices including organic photovoltaics, field-effect transistors (OFETs), and light-emitting diodes (OLEDs), − showing capabilities of improving carrier mobility, tuning band gap energies or interfacial properties, and so forth. − Despite these merits, introducing molecular dopants into the bulk film of bulk heterojunction (BHJ) organic solar cells (OSCs) is often worried by the negative changes in nanomorphology or molecular ordering at higher dopant concentration or merely visible (positive) effects at diluted dopant concentration. − These difficulties have been encountered in the attempts of doping of nonfullerene (NF) OSCs with widely used 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) for reasons that are yet not fully understood.…”

Concepts and principles of self-n-doping in perylene diimide chromophores for applications in biochemistry, energy harvesting, energy storage, and catalysis

“…A diverse range of self-n-doped materials have been reported as efficient ETLs and cathode interlayers in solar cells, some with benchmark performances. [22][23][24]31,[189][190][191][192][193][194] Numerous examples were recently reviewed elsewhere in excellent detail. 195 N-PDIs have been shown to increase the broadband absorption of active layers, improve ETL homogeneity, and enhance solvent orthogonality for improved processability of BHJs.…”