Molecular Structure‐Dependent Charge Injection and Doping Efficiencies of Organic Semiconductors: Impact of Side Chain Substitution

Due to the highly anisotropic nature of π ‐conjugated molecules, the molecular structure of organic semiconductors can significantly affect the device performance of organic optoelectronics. Here, the molecular structure dependence on charge injection and doping efficiencies is investigated by characterizing the typical hole transport material of N,N′‐bis(naphthalen‐1‐yl)‐N,N′‐bis(phenyl)‐benzidine (NPB) and its derivatives N,N′‐bis(naphthalen‐1‐yl)‐N,N′‐bis(phenyl)‐9,9‐dimethyl‐fluorene (DMFL‐NPB) and N,N′‐bis(naphthalen‐1‐yl)‐N,N′‐bis(phenyl)‐9,9‐diphenyl‐fluorene (DPFL‐NPB)]. Using photoelectron spectroscopy data and density functional theory calculation, it is identified that the side chain substitution in NPB and its derivatives plays a crucial role in the intrinsic injection and transport properties, and doping efficiency. The inner twist of the two main benzene rings in NPB is changed from out‐of‐plane to in‐plane due to the alkyl or phenyl side chains of DMFL‐NPB or DPFL‐NPB, which reduces the ionization energies and thus decreases the hole injection barriers at the indium tin oxide/organic interface. The doping efficiency in 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄‐TCNQ) doped systems is also highly dependent on the degree of intermolecular orbital energy hybridization with respect to the side chain substitution. These findings show that the rational design of molecular structures with suitable side chains is crucial for achieving high‐performance organic devices.     

N‐Type Organic Thermoelectrics: Improved Power Factor by Tailoring Host–Dopant Miscibility

In this contribution, for the first time, the polarity of fullerene derivatives is tailored to enhance the miscibility between the host and dopant molecules. A fullerene derivative with a hydrophilic triethylene glycol type side chain (PTEG‐1) is used as the host and (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine n ‐DMBI) as the dopant. Thereby, the doping efficiency can be greatly improved to around 18% (<1% for a nonpolar reference sample) with optimized electrical conductivity of 2.05 S cm^?1, which represents the best result for solution‐processed fullerene derivatives. An in‐depth microstructural study indicates that the PTEG‐1 molecules readily form layered structures parallel to the substrate after solution processing. The fullerene cage plane is alternated by the triethylene glycol side chain plane; the n ‐DMBI dopants are mainly incorporated in the side chain plane without disturbing the π–π packing of PTEG‐1. This new microstructure, which is rarely observed for codeposited thin films from solution, formed by PTEG‐1 and n ‐DMBI molecules explains the increased miscibility of the host/dopant system at a nanoscale level and the high electrical conductivity. Finally, a power factor of 16.7 µW m^?1 K^?2 is achieved at 40% dopant concentration. This work introduces a new strategy for improving the conductivity of solution‐processed n‐type organic thermoelectrics.     

Polar Side Chains Enhance Processability,Electrical Conductivity,and Thermal Stability of a Molecularly p‐Doped Polythiophene

Molecular doping of organic semiconductors is critical for optimizing a range of optoelectronic devices such as field‐effect transistors, solar cells, and thermoelectric generators. However, many dopant:polymer pairs suffer from poor solubility in common organic solvents, which leads to a suboptimal solid‐state nanostructure and hence low electrical conductivity. A further drawback is the poor thermal stability through sublimation of the dopant. The use of oligo ethylene glycol side chains is demonstrated to significantly improve the processability of the conjugated polymer p(g₄2T‐T)—a polythiophene—in polar aprotic solvents, which facilitates coprocessing of dopant:polymer pairs from the same solution at room temperature. The use of common molecular dopants such as 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) is explored. Doping of p(g₄2T‐T) with F4TCNQ results in an electrical conductivity of up to 100 S cm^?1. Moreover, the increased compatibility of the polar dopant F4TCNQ with the oligo ethylene glycol functionalized polythiophene results in a high degree of thermal stability at up to 150 °C.     

Controllable,Wide‐Ranging n‐Doping and p‐Doping of Monolayer Group 6 Transition‐Metal Disulfides and Diselenides

Developing processes to controllably dope transition‐metal dichalcogenides (TMDs) is critical for optical and electrical applications. Here, molecular reductants and oxidants are introduced onto monolayer TMDs, specifically MoS₂, WS₂, MoSe₂, and WSe₂. Doping is achieved by exposing the TMD surface to solutions of pentamethylrhodocene dimer as the reductant (n‐dopant) and “Magic Blue,” [N(C₆H₄‐p‐Br)₃]SbCl₆, as the oxidant (p‐dopant). Current–voltage characteristics of field‐effect transistors show that, regardless of their initial transport behavior, all four TMDs can be used in either p‐ or n‐channel devices when appropriately doped. The extent of doping can be controlled by varying the concentration of dopant solutions and treatment time, and, in some cases, both nondegenerate and degenerate regimes are accessible. For all four TMD materials, the photoluminescence intensity; for all four materials the PL intensity is enhanced with p‐doping but reduced with n‐doping. Raman and X‐ray photoelectron spectroscopy (XPS) also provide insight into the underlying physical mechanism by which the molecular dopants react with the monolayer. Estimates of changes of carrier density from electrical, PL, and XPS results are compared. Overall a simple and effective route to tailor the electrical and optical properties of TMDs is demonstrated.     

25th Anniversary Article: High‐Mobility Hole and Electron Transport Conjugated Polymers: How Structure Defines Function

The structural organization of three different families of semicrystalline π‐conjugated polymers is reported (poly(3‐hexylthiophene) (P3HT), poly[2,6‐(4,4‐bis‐alkyl‐4H‐cyclopenta‐[2,1‐b;3,4‐b0]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)](cyclopentadithiophene‐benzothiadiazole) (CDT‐BTZ) and poly(N,N"‐bis‐2‐octyldodecylnaphtalene‐1,4,5,8‐bis‐dicarboximide‐2,6‐diyl‐alt‐5,5–2,2‐bithiophene (P(NDI2OD‐T2))). These have triggered significant interest for their remarkable charge‐transport properties. By performing molecular mechanics/dynamics simulations with carefully re‐parameterized force fields, it is illustrated in particular how the supramolecular organization of these conjugated polymers is driven by an interplay between the length and nature of the conjugated monomer unit and the packing of their alkyl side chains, and to what extent it impacts the charge‐carrier mobility, as monitored by quantum‐chemical calculations of the intermolecular hopping transfer integrals. This Progress Report is concluded by providing generic guidelines for the design of materials with enhanced degrees of supramolecular organization.     

Side Chain Engineering on Medium Bandgap Copolymers to Suppress Triplet Formation for High‐Efficiency Polymer Solar Cells

Suppression of carrier recombination is critically important in realizing high‐efficiency polymer solar cells. Herein, it is demonstrated difluoro‐substitution of thiophene conjugated side chain on donor polymer can suppress triplet formation for reducing carrier recombination. A new medium bandgap 2D‐conjugated D–A copolymer J91 is designed and synthesized with bi(alkyl‐difluorothienyl)‐benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit, for taking the advantages of the synergistic fluorination on the backbone and thiophene side chain. J91 demonstrates enhanced absorption, low‐lying highest occupied molecular orbital energy level, and higher hole mobility, in comparison with its control polymer J52 without fluorination on the thiophene side chains. The transient absorption spectra indicate that J91 can suppress the triplet formation in its blend film with n‐type organic semiconductor acceptor m ‐ITIC (3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene). With these favorable properties, a higher power conversion efficiency of 11.63% with high V _OC of 0.984 V and high J _SC of 18.03 mA cm^?2 is obtained for the polymer solar cells based on J91 /m ‐ITIC with thermal annealing. The improved photovoltaic performance by thermal annealing is explained from the morphology change upon thermal annealing as revealed by photoinduced force microscopy. The results indicate that side chain engineering can provide a new solution to suppress carrier recombination toward high efficiency, thus deserves further attention.     

A Chemically Doped Naphthalenediimide‐Bithiazole Polymer for n‐Type Organic Thermoelectrics

The synthesis of a novel naphthalenediimide (NDI)‐bithiazole (Tz2)‐based polymer [P(NDI2OD‐Tz2)] is reported, and structural, thin‐film morphological, as well as charge transport and thermoelectric properties are compared to the parent and widely investigated NDI‐bithiophene (T2) polymer [P(NDI2OD‐T2)]. Since the steric repulsions in Tz2 are far lower than in T2, P(NDI2OD‐Tz2) exhibits a more planar and rigid backbone, enhancing π–π chain stacking and intermolecular interactions. In addition, the electron‐deficient nature of Tz2 enhances the polymer electron affinity, thus reducing the polymer donor–acceptor character. When n‐doped with amines, P(NDI2OD‐Tz2) achieves electrical conductivity (≈0.1 S cm^?1) and a power factor (1.5 µW m^?1 K^?2) far greater than those of P(NDI2OD‐T2) (0.003 S cm^?1 and 0.012 µW m^?1 K^?2, respectively). These results demonstrate that planarized NDI‐based polymers with reduced donor–acceptor character can achieve substantial electrical conductivity and thermoelectric response.     

High Conductivity and Electron‐Transfer Validation in an n‐Type Fluoride‐Anion‐Doped Polymer for Thermoelectrics in Air

Air‐stable and soluble tetrabutylammonium fluoride (TBAF) is demonstrated as an efficient n‐type dopant for the conjugated polymer ClBDPPV. Electron transfer from F^? anions to the π‐electron‐deficient ClBDPPV through anion–π electronic interactions is strongly corroborated by the combined results of electron spin resonance, UV–vis–NIR, and ultraviolet photoelectron spectroscopy. Doping of ClBDPPV with 25 mol% TBAF boosts electrical conductivity to up to 0.62 S cm^?1, among the highest conductivities that have been reported for solution‐processed n‐type conjugated polymers, with a thermoelectric power factor of 0.63 µW m^?1 K^?2 in air. Importantly, the Seebeck coefficient agrees with recently published correlations to conductivity. Moreover, the F^?‐doped ClBDPPV shows significant air stability, maintaining the conductivity of over 0.1 S cm^?1 in a thick film after exposure to air for one week, to the best of our knowledge the first report of an air‐stable solution‐processable n‐doped conductive polymer with this level of conductivity. The result shows that using solution‐processable small‐anion salts such as TBAF as an n‐dopant of organic conjugated polymers possessing lower LUMO (lowest unoccupied molecular orbital), less than ?4.2 eV) can open new opportunities toward high‐performance air‐stable solution‐processable n‐type thermoelectric (TE) conjugated polymers.     

Improvement of Electrical Conductivity in Conjugated Polymers through Cascade Doping with Small-Molecular Dopants

Doping capability is primitively governed by the energy level offset between the highest occupied molecular orbital (HOMO) of conjugated polymers (CPs) and the lowest unoccupied molecular orbital (LUMO) of dopants. A poor doping efficiency is obtained when doping directly using NOBF₄ forming a large energy offset with the CP, while the devised doping strategy is found to significantly improve the doping efficiency (electrical conductivity) by sequentially treating the NOBF₄ to the pre-doped CP with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquino-dimethane (F4TCNQ), establishing a relatively small energy level offset. It is verified that the cascade doping strategy requires receptive sites for each dopant to further improve the doping efficiency, and provides fast reaction kinetics energetically. An outstanding electrical conductivity (>610 S cm⁻¹) is achieved through the optimization of the devised doping strategy, and spectroscopy analysis, including Hall effect measurement, supports more efficient charge carrier generation via the devised cascade doping.     

Saturated and unsaturated aliphatic side chain-appended naphthalenediimide derivatives: synthesis and structure property relationship

Previous studies have shown influence of aliphatic side chain length and type on the transport properties of naphthalenediimide (NDI) materials by affecting molecular arrangement. There is lack of comparative study on the presence or absence of unsaturation in side chain and its effect on optical and electronic properties of NDI. The present work focuses on the structure–property relationship of four NDI derivatives bearing octyl (C8, OctA-NDI), hexadecyl (C16, HD-NDI), octadecyl (C18, ODA-NDI) and oleyl (C18-un, unsaturated, OLA-NDI) chain on imide-nitrogen. The self-assembling behaviour of the molecules is studied in concentrated solutions as fresh and aged samples in four different solvents by absorbance and emission spectroscopy. With increase in alkyl chain length, the aggregation behaviour is observed to increase. Very interestingly introduction of unsaturation in side chain reduces aggregation and restores the monomeric properties. Self-assembled microstructures formation was studied by scanning electron microscopy where all the four materials show different types of self-assembly formation. Finally, we compared the thermally activated electron conductivity and electron mobility of NDI derivatives, where also the side chain structure clearly influences the electron transport. Electron mobility decreases on increasing chain length from C8 to C18 and again increases in C18-un. A rationale for the structure–property relationship has been given based on the molecular packing and intermolecular π–π interactions. This study contributes significantly towards designing new NDI derivatives bearing long side chains with hampered aggregation for niche applications.

     

Quartz crystal microbalance and spectroscopy measurements for acid doping in polyaniline films

Abstract

We investigated the doping of thin polyaniline (PANI) films, prepared by the chemical oxidation of aniline, with different acids. The initial step in the investigation is the preparation of PANI films from aqueous hydrochloric acid solution. This is followed by dedoping with ammonia to obtain a PANI base, which is subsequently doped with strong acids (e.g. hydrochloric, sulfuric, phosphoric and trichloroacetic acids) and with a weak acid (acetic acid). The dopant weight fraction (w), which is connected with the gain of mass during the doping of PANI, was determined in situ using a quartz crystal microbalance (QCM). The behavior of PANI upon doping with different anions derived from strong acids indicates that both proton and the anion uptake into the polymer chains occur sharply, rapidly, completely, and reversibly. However the uptake in the case in acetic acid is characterized by slow diffusion. The doping was studied at different concentrations of acetic acid. A second cycle of dedoping–redoping was also performed. The kinetics of the doping reaction is dominated by Fickian diffusion kinetics. The diffusion coefficients (D) of the dopant ions into the PANI chains were determined using the QCM and by UV–Vis absorption spectroscopy in the range of (0.076–1.64)× 10^?15 cm² s^?1. It was found that D in the second cycle of doping is larger than that evaluated from the first cycle of doping for high concentrations of acetic acid. D for the diffusion and for the dopant ion expulsion from the PANI chains was also determined during the redoping process. It was found that D for acetic acid ions in the doping process is larger than that calculated for the dedoping process.     

Doping GaP Core–Shell Nanowire pn‐Junctions: A Study by Off‐Axis Electron Holography

The doping process in GaP core–shell nanowire pn‐junctions using different precursors is evaluated by mapping the nanowires' electrostatic potential distribution by means of off‐axis electron holography. Three precursors, triethyltin (TESn), ditertiarybutylselenide, and silane are investigated for n‐type doping of nanowire shells; among them, TESn is shown to be the most efficient precursor. Off‐axis electron holography reveals higher electrostatic potentials in the regions of nanowire cores grown by the vapor–liquid–solid (VLS) mechanism (axial growth) than the regions grown parasitically by the vapor–solid (VS) mechanism (radial growth), attributed to different incorporation efficiency between VLS and VS of unintentional p‐type carbon doping originating from the trimethylgallium precursor. This study shows that off‐axis electron holography of doped nanowires is unique in terms of the ability to map the electrostatic potential and thereby the active dopant distribution with high spatial resolution.     

Conductivity Tuning via Doping with Electron Donating and Withdrawing Molecules in Perovskite CsPbI3 Nanocrystal Films

Doping of semiconductors enables fine control over the excess charge carriers, and thus the overall electronic properties, crucial to many technologies. Controlled doping in lead‐halide perovskite semiconductors has thus far proven to be difficult. However, lower dimensional perovskites such as nanocrystals, with their high surface‐area‐to‐volume ratio, are particularly well‐suited for doping via ground‐state molecular charge transfer. Here, the tunability of the electronic properties of perovskite nanocrystal arrays is detailed using physically adsorbed molecular dopants. Incorporation of the dopant molecules into electronically coupled CsPbI₃ nanocrystal arrays is confirmed via infrared and photoelectron spectroscopies. Untreated CsPbI₃ nanocrystal films are found to be slightly p‐type with increasing conductivity achieved by incorporating the electron‐accepting dopant 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) and decreasing conductivity for the electron‐donating dopant benzyl viologen. Time‐resolved spectroscopic measurements reveal the time scales of Auger‐mediated recombination in the presence of excess electrons or holes. Microwave conductance and field‐effect transistor measurements demonstrate that both the local and long‐range hole mobility are improved by F₄TCNQ doping of the nanocrystal arrays. The improved hole mobility in photoexcited p‐type arrays leads to a pronounced enhancement in phototransistors.     

Reversible and Precisely Controllable p/n‐Type Doping of MoTe2 Transistors through Electrothermal Doping

Precisely controllable and reversible p/n‐type electronic doping of molybdenum ditelluride (MoTe₂) transistors is achieved by electrothermal doping (E‐doping) processes. E‐doping includes electrothermal annealing induced by an electric field in a vacuum chamber, which results in electron (n‐type) doping and exposure to air, which induces hole (p‐type) doping. The doping arises from the interaction between oxygen molecules or water vapor and defects of tellurium at the MoTe₂ surface, and allows the accurate manipulation of p/n‐type electrical doping of MoTe₂ transistors. Because no dopant or special gas is used in the E‐doping processes of MoTe₂, E‐doping is a simple and efficient method. Moreover, through exact manipulation of p/n‐type doping of MoTe₂ transistors, quasi‐complementary metal oxide semiconductor adaptive logic circuits, such as an inverter, not or gate, and not and gate, are successfully fabricated. The simple method, E‐doping, adopted in obtaining p/n‐type doping of MoTe₂ transistors undoubtedly has provided an approach to create the electronic devices with desired performance.     

2D Binary Plasmonic Nanoassemblies with Semiconductor n/p‐Doping‐Like Properties

The electronic, optical, thermal, and magnetic properties of an extrinsic bulk semiconductor can be finely tuned by adjusting its dopant concentration. Here, it is demonstrated that such a doping concept can be extended to plasmonic nanomaterials. Using two‐dimensional (2D) assemblies of Au@Ag and Au nanocubes (NCs) as a model system, detailed experimental and theoretical studies are carried out, which reveal collective semiconductor n/p‐doping‐like plasmonic properties. A threshold doping concentration of Au@Ag NCs is observed, below which p‐doping dominates and above which n‐doping prevails. Furthermore, Au@Ag NC dopants can be converted into corresponding Au seed “voids” dopants by selectively removing Ag without changing the overall structural integrity. The results show that the plasmonic doping concept may serve as a general design principle guiding synthesis and assembly of plasmonic metamaterials for programmable optoelectronic devices.     

Dual‐Additive Assisted Chemical Vapor Deposition for the Growth of Mn‐Doped 2D MoS2 with Tunable Electronic Properties

Doping of bulk silicon and III–V materials has paved the foundation of the current semiconductor industry. Controlled doping of 2D semiconductors, which can also be used to tune their bandgap and type of carrier thus changing their electronic, optical, and catalytic properties, remains challenging. Here the substitutional doping of nonlike element dopant (Mn) at the Mo sites of 2D MoS₂ is reported to tune its electronic and catalytic properties. The key for the successful incorporation of Mn into the MoS₂ lattice stems from the development of a new growth technology called dual‐additive chemical vapor deposition. First, the addition of a MnO₂ additive to the MoS₂ growth process reshapes the morphology and increases lateral size of Mn‐doped MoS₂. Second, a NaCl additive helps in promoting the substitutional doping and increases the concentration of Mn dopant to 1.7 at%. Because Mn has more valance electrons than Mo, its doping into MoS₂ shifts the Fermi level toward the conduction band, resulting in improved electrical contact in field effect transistors. Mn doping also increases the hydrogen evolution activity of MoS₂ electrocatalysts. This work provides a growth method for doping nonlike elements into 2D MoS₂ and potentially many other 2D materials to modify their properties.     

Volatile organic compound detection using nanostructured copolymers

Regioregular polythiophene-based conductive copolymers with highly crystalline nanostructures are shown to hold considerable promise as the active layer in volatile organic compound (VOC) chemresistor sensors. While the regioregular polythiophene polymer chain provides a charge conduction path, its chemical sensing selectivity and sensitivity can be altered either by incorporating a second polymer to form a block copolymer or by making a random copolymer of polythiophene with different alkyl side chains. The copolymers were exposed to a variety of VOC vapors, and the electrical conductivity of these copolymers increased or decreased depending upon the polymer composition and the specific analytes. Measurements were made at room temperature, and the responses were found to be fast and appeared to be completely reversible. Using various copolymers of polythiophene in a sensor array can provide much better discrimination to various analytes than existing solid state sensors. Our data strongly indicate that several sensing mechanisms are at play simultaneously, and we briefly discuss some of them.     

Synergistic Impacts of Electrolyte Adsorption on the Thermoelectric Properties of Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes are promising candidates for light‐weight and flexible energy materials. Recently, the thermoelectric properties of single‐walled carbon nanotubes have been dramatically improved by ionic liquid addition; however, controlling factors remain unsolved. Here the thermoelectric properties of single‐walled carbon nanotubes enhanced by electrolytes are investigated. Complementary characterization with absorption, Raman, and X‐ray photoelectron spectroscopy reveals that shallow hole doping plays a partial role in the enhanced electrical conductivity. The molecular factors controlling the thermoelectric properties of carbon nanotubes are systematically investigated in terms of the ionic functionalities of ionic liquids. It is revealed that appropriate ionic liquids show a synergistic enhancement in conductivity and the Seebeck coefficient. The discovery of significantly precise doping enables the generation of thermoelectric power factor exceeding 460 µW m^–1 K^–2.     

n‐Type Doped Conjugated Polymer for Nonvolatile Memory

This study demonstrates a facile way to efficiently induce strong memory behavior from common p‐type conjugated polymers by adding n‐type dopant 2‐(2‐methoxyphenyl)‐1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazole. The n‐type doped p‐channel conjugated polymers not only enhance n‐type charge transport characteristics of the polymers, but also facilitate to storage charges and cause reversible bistable (ON and OFF states) switching upon application of gate bias. The n‐type doped memory shows a large memory window of up to 47 V with an on/off current ratio larger than 10 000. The charge retention time can maintain over 100 000 s. Similar memory behaviors are also observed in other common semiconducting polymers such as poly(3‐hexyl thiophene) and poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene], and a high mobility donor–acceptor polymer, poly(isoindigo‐bithiophene). In summary, these observations suggest that this approach is a general method to induce memory behavior in conjugated polymers. To the best of the knowledge, this is the first report for p‐type polymer memory achieved using n‐type charge‐transfer doping.     

Conjugated‐Polyelectrolyte‐Functionalized Reduced Graphene Oxide with Excellent Solubility and Stability in Polar Solvents

Conjugated‐polyelectrolyte (CPE)‐functionalized reduced graphene oxide (rGO) sheets are synthesized for the first time by taking advantage of a specially designed CPE, PFVSO₃, with a planar backbone and charged sulfonate and oligo(ethylene glycol) side chains to assist the hydrazine‐mediated reduction of graphene oxide (GO) in aqueous solution. The resulting CPE‐functionalized rGO (PFVSO₃‐rGO) shows excellent solubility and stability in a variety of polar solvents, including water, ethanol, methanol, dimethyl sulfoxide, and dimethyl formamide. The morphology of PFVSO₃‐rGO is studied by atomic force microscopy, X‐ray diffraction, and transmission electron microscopy, which reveal a sandwich‐like nanostructure. Within this nanostructure, the backbones of PFVSO₃ stack onto the basal plane of rGO sheets via strong π–π interactions, while the charged hydrophilic side chains of PFVSO₃ prevent the rGO sheets from aggregating via electrostatic and steric repulsions, thus leading to the solubility and stability of PFVSO₃‐rGO in polar solvents. Optoelectronic studies show that the presence of PFVSO₃ within rGO induces photoinduced charge transfer and p‐doping of rGO. As a result, the electrical conductivity of PFVSO₃‐rGO is not only much better than that of GO, but also than that of the unmodified rGO.