Donor copolymer with benzo[1,2‐b:4,5‐b′]dithiophene and quinoxaline derivative segments for photovoltaic applications

A donor copolymer Poly{2,6‐4,8‐bis(2‐ethylhexyl)benzo[1,2‐b:3,4‐b′]dithiophene‐5,8‐2,3‐bis(5‐octylthiophen‐2‐yl)quinoxaline} (PBDTThQx) with benzo[1,2‐b:4,5‐b′]dithiophene and quinoxaline derivatives was synthesized and characterized with NMR, ultraviolet–visible spectroscopy, thermogravimetric analyses, and cyclic voltammetry. Photovoltaic devices with the configuration indium tin oxide–poly(3,4‐ethylenedioxythiophene)–poly(styrene sulfonate)–PBDTThQx–[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM)–LiF–Al were fabricated, in which PBDTThQx performed as the electron donor and PC₆₁BM was the electron acceptor in the active layer. The device presented reasonable photovoltaic properties when the weight ratio of PBDTThQx:PC₆₁BM reached 1:3. The open‐circuit voltage, fill factor, and power conversion efficiency were gauged to be 0.75 V, 0.59, and 0.74%, respectively. The experimental data implied that PBDTThQx would be a promising donor candidate in the application of polymer solar cells. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40279.     

Synthesis of two D‐π‐A polymers π‐bridged by different blocks and investigation of their photovoltaic property

The synthesis, characterization, photophysical and photovoltaic properties of two 5,6‐bis(octyloxy)benzo[c][1,2,5]thiadiazole‐containing wide‐band‐gap donor and acceptor D‐π‐A alternating conjugated polymers (HSD‐a and HSD‐b) have been reported. These two polymers absorb in the range of 300–700 nm with a band gap of about 1.88 and 1.97 eV. The HOMO energy levels were ?5.44 eV for HSD‐a and ?5.63 eV for HSD‐b. Polymer solar cells with HSD‐b :PC₇₁BM as the active layer demonstrated a power conversion efficiency (PCE) of 2.59% with a high V_oc of 0.93 V, a J_sc of 7.3 mA/cm², and a comparable fill factor (FF) of 0.38 under simulated solar illumination of AM 1.5G (100 mW/cm²) without annealing. In addition, HSD‐a :PC₇₁BM blend‐based solar cells exhibit a PCE of 2.15% with a comparable V_oc of 0.64 V, J_sc of 8.75 mA/cm^?2, and FF of 0.40. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41587.     

Correlation between the performance of organic bulk‐heterojunction solar cells and the molecular structures of alcohol solvents

Morphology control is an important issue for boosting the performance of organic bulk‐heterojunction (BHJ) solar cells. In this study, we investigated the correlation between alcohol solvents and the morphologies of poly({4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′] dithiophene‐2,6‐diyl}{3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl}) (PTB7) and [6,6]‐phenyl‐C₇₀‐butyric acid methyl ester (PC₇₀BM)‐based organic solar cells by spin‐casting the alcohol onto the active layers. We found that the morphologies strongly depended on the structure of the alcohol [alkyl chain length and hydroxyl (? OH) group position]. Ethanol or 2‐propanol showed the highest performance among the alcohols considered here. Atomic force microscopy images and absorption spectra demonstrated that the alcohols affected the morphologies of PC₇₀BM rather than those of PTB7. The morphologies of PC₇₀BM were dependent on the solubilities of the alcohols to the active layers and the hydrogen‐bonding strengths between the PC₇₀BM and alcohol molecules. Our results indicate that the use of alcohols for solvent annealing is a simple and efficient method for developing high‐performance organic BHJ solar cells. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 44367.     

Improved stability in P3HT:PCBM photovoltaics by incorporation of well‐designed polythiophene/graphene compositions

Morphological and photovoltaic stabilities of poly(3‐hexylthiophene) (P3HT):phenyl‐C₆₁‐butyric acid methyl ester (PC₇₁BM) solar cells were investigated in pristine and modified states. To this end, four types of patterned/assembled nanostructures, namely reduced graphene oxide (rGO)‐g‐poly(3‐dodecylthiophene)/P3HT patched‐like pattern, rGO–polythiophene/P3HT/PC₇₁BM nanofiber, rGO‐g‐P3HT/P3HT cake‐like pattern and supra(polyaniline (PANI)‐g‐rGO/P3HT), were designed on the basis of rGO and various conjugated polymers. Intermediately covered rGO nanosheets by P3HT crystals (supra(PANI‐g‐rGO/P3HT)) performed better than sparsely (patched‐like pattern) and fully (cake‐like pattern) covered ones in P3HT:PC₇₁BM solar cell systems. Supra(PANI‐g‐rGO/P3HT) nanohybrids largely phase‐separated in active layers (root mean square = 0.88 nm) and also led to the highest performance (power conversion efficiency of 5.74%). The photovoltaic characteristics demonstrated decreasing trends during air aging for all devices, but with distinct slopes. The steepest decreasing plots were obtained for the unmodified P3HT:PC₇₁BM devices (from 1.77% to 0.28%). The two supramolecules with the most ordered structures, that is, cake‐like pattern (10.12 mA cm^?2, 51%, 0.58 V, 2.2 × 10^?6 cm² V^?1 s^?1, 4.3 × 10^?5 cm² V^?1 s^?1, 0.69 nm and 2.99%) and supra(PANI‐g‐rGO/P3HT) (12.51 mA cm^?2, 57%, 0.63 V, 1.2 × 10^?5 cm² V^?1 s^?1, 3.4 × 10^?4 cm² V^?1 s^?1, 0.82 nm and 4.49%), strongly retained morphological and photovoltaic stabilities in P3HT:PC₇₁BM devices after 1 month of air aging. According to the morphological, optical, photovoltaic and electrochemical results, the supra(PANI‐g‐rGO/P3HT) nanohybrid was the best candidate for stabilizing P3HT:PC₇₁BM solar cells. © 2020 Society of Chemical Industry     

Efficient polymer solar cells utilizing solution-processed interlayer based on different conjugated backbones

The poor energy conversion efficiency for those polymer solar cells (PSCs) creates an obstacle for their commercialization. Inspired by this issue, two cathode interlayers, PBTBTz-TMAI and PBTzPh-TMAI based on benzothiadiazole (BT) and benzotriazole (BTz)-conjugated or benzene (Ph) and BTz-conjugated alternating units (both exhibits the same tetravalent amine-end side chain), were synthesized via Suzuki coupling polymerization and trivalent amine-end ionization. When PBTBTz-TMAI and PBTzPh-TMAI were utilized as cathode interlayers in PSCs, the charge-carrier transfer from active layer to cathode electrode was significantly improved, accompanied by an optimized exciton dissociation efficiency, primarily attributed to the introduction of tetravalent amine groups. Consequently, the device with PBTBTz-TMAI exhibited power conversion efficiencies (PCEs) = 8.3 and 10.5% for the PTB7:PC₇₁BM-based and PBDB-T:ITIC-based PSCs, respectively. In parallel, devices with a PBTzPh-TMAI cathode interlayer (that were established on the active layers of PTB7:PC₇₁BM and PBDB-T:ITIC) obtained a remarkably superior optoelectric efficiency with PCEs = 8.5 and 10.8%. These findings offer an alternative tactic toward to high efficiency PSCs to meet the increasing energy crisis.     

Effects of high-boiling-point additive 2-Bromonaphthalene on polymer solar cells fabricated in ambient air

High boiling point solvent additive, employed during the solution processing of active layer fabrications, impact the efficiency of bulk heterojunction polymer solar cells (PSC) by influencing the morphological of the active layer. The photovoltaic performances of the PSCs based on the donor of poly{4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]-dithiophene-2,6-diyl-alt-3-fluoro-2-[(2 ethylhexyl)carbonyl] thieno[3,4-b]thiophene-4,6-diy (PTB7) and the acceptor of [6, 6]-phenyl-C71-butyric-acidmethyl-ester (PC₇₁BM) was optimized using 5 vol% high-boiling-point solvent additive of 2-Bromonaphthalene (BN). The optimized air-processed PSC based on PTB7:PC₇₁BM (1:1.5 w/w) with 5 vol% BN exhibited a power conversion efficiency of 7.01% with open-circuit voltage (V _oc) of 0.731 V, short-circuit current density (J _sc) of 13.79 mA cm^?2, and fill factor (FF) of 69.46%. The effects of the additive on photovoltaic performances were illustrated with atomic force microscopy and transmission electron microscope measurements. Our results indicate that the improved efficiency is due to the optimized PTB7/PC₇₁BM interpenetrating network and the enhanced absorption of the active layer using the BN as solvent additive.     

New low bandgap conjugated polymer derived from 2, 7‐carbazole and 5, 6‐bis(octyloxy)‐4, 7‐di(thiophen‐2‐yl) benzothiadiazole: Synthesis and photovoltaic properties

To develop conjugated polymers with low bandgap, deep HOMO level, and good solubility, a new conjugated alternating copolymer PC‐DODTBT based on N‐9′‐heptadecanyl‐2,7‐carbazole and 5, 6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)benzothiadiazole was synthesized by Suzuki cross‐coupling polymerization reaction. The polymer reveals excellent solubility and thermal stability with the decomposition temperature (5% weight loss) of 327°C. The HOMO level of PC‐DODTBT is ‐5.11 eV, indicating that the polymer has relatively deep HOMO level. The hole mobility of PC‐DODTBT as deduced from SCLC method was found to be 2.03 × 10^?4 cm²/Versus Polymer solar cells (PSCs) based on the blends of PC‐DODTBT and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) with a weight ratio of 1:2.5 were fabricated. Under AM 1.5 (AM, air mass), 100 mW/cm^?2 illumination, the devices were found to exhibit an open‐circuit voltage (V_oc) of 0.73 V, short‐circuit current density (J_sc) of 5.63 mA/cm^?2, and a power conversion efficiency (PCE) of 1.44%. This photovoltaic performance indicates that the copolymer is promising for polymer solar cells applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Well‐functioned photovoltaics based on nanofibers composed of PBDT‐TIPS‐DTNT‐DT and graphenic precursors thermally modified by polythiophene,polyaniline and polypyrrole

Reduced graphene oxide nanosheets modified by conductive polymers including polythiophene (GPTh), polyaniline (GPANI) and polypyrrole (GPPy) were prepared using the graphene oxide as both substrate and chemical oxidant. UV–visible and Raman analyses confirmed that the graphene oxide simultaneously produced the reduced graphene oxide and polymerized the conjugated polymers. The prepared nanostructures were subsequently electrospun in mixing with poly(3‐hexylthiophene) (P3HT)/phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) and poly[bis(triisopropylsilylethynyl)benzodithiophene‐bis(decyltetradecylthien)naphthobisthiadiazole] (PBDT‐TIPS‐DTNT‐DT)/PC₇₁BM components and embedded in the active layers of photovoltaic devices to improve the charge mobility and efficiency. The GPTh/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM devices demonstrated better photovoltaic features (J_sc = 11.72 mA cm^?2, FF = 61%, V_oc = 0.68 V, PCE = 4.86%, μ_h = 8.7 × 10^?3 cm² V^–1 s^?1 and μ_e = 1.3 × 10^?2 cm² V^–1 s^?1) than the GPPy/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.30 mA cm^?2, FF = 60%, V_oc = 0.66 V, PCE = 4.08%, μ_h = 1.4 × 10^?3 cm² V^–1 s^?1 and μ_e = 8.9 × 10^?3 cm² V^–1 s^?1) and GPANI/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.48 mA cm^?2, FF = 59%, V_oc = 0.65 V, PCE = 4.02%, μ_h = 8.6 × 10^?4 cm² V^–1 s^?1 and μ_e = 7.8 × 10^?3 cm² V^–1 s^?1) systems, assigned to the greater compatibility of PTh in the nano‐hybrids and the thiophenic conjugated polymers in the bulk of the nanofibers and active thin films. Furthermore, the PBDT‐TIPS‐DTNT‐DT polymer chains (3.35%–5.04%) acted better than the P3HT chains (2.01%–3.76%) because of more complicated conductive structures. © 2019 Society of Chemical Industry     

Pure and complex nanostructures using poly[bis(triiso‐propylsilylethynyl) benzodithiophene‐bis(decyltetradecyl‐thien) naphthobisthiadiazole], carbon nanotubes and reduced graphene oxide for high‐performance polymer solar cells

Crystallization of poly[bis(triiso‐propylsilylethynyl) benzodithiophene‐bis(decyltetradecyl‐thien) naphthobisthiadiazole] (PBDT‐TIPS‐DTNT‐DT) was investigated in supramolecules based on carbon nanotubes (CNTs) and reduced graphene oxide (rGO) and their grafted derivatives. The principal peaks of PBDT‐TIPS‐DTNT‐DT crystals were in the range 3.50°–3.75°. By grafting the surface of the carbonic materials, the assembling of polymer chains decreased because of hindrance of poly(3‐dodecylthiophene) (PDDT) grafts against π‐stacking. The diameters of CNT/polymer and CNT‐g‐PDDT/polymer supramolecules were 160 and 100 nm. The rGO/polymer supramolecules had the highest melting point (T_m = 282 °C) and fusion enthalpy (ΔH_m = 25.98 J g^?1), reflecting the largest crystallites and the most ordered constituents. Nano‐hybrids based on grafted rGO (276 °C and 28.26 J g^?1), CNT (275 °C and 27.32 J g^?1) and grafted CNT (268 °C and 22.17 J g^?1) were also analyzed. T_m and ΔH_m values were significantly less in corresponding melt‐grown systems. The nanostructures were incorporated in active layers of PBDT‐TIPS‐DTNT‐DT:phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) solar cells to improve the photovoltaic features. The best results were detected for PBDT‐TIPS‐DTNT‐DT:PC₇₁BM:rGO/polymer systems having J_sc = 13.11 mA cm^?2, fill factor 60% and V_oc = 0.71 V with an efficacy of 5.58%. On grafting the rGO and CNT, efficiency reductions were 12.01% (5.58%–4.91%) and 9.34% (4.07%–3.69%), respectively. © 2019 Society of Chemical Industry     

Synthesis and solar cells applications of EO‐PF‐DTBT polymer

Poly{[2,7‐(9,9‐bis‐(1‐(2‐(2‐methoxyethoxy)ethoxy)ethyl)‐fluorene)]‐alt‐[5,5‐(4,7‐di‐2′‐thienyl‐2,1,3‐benzothiadiazole)]} (EO‐PF‐DTBT) was synthesized by Suzuki coupling reaction. The polymer is soluble in common organic solvent, such as toluene, THF, and chloroform, and it also shows solubility in polar solvent, such as cyclopentanone. Solar cells based on EO‐PF‐DTBT and PC₆₁BM show maximum power conversion efficiency of 2.65% with an open circuit voltage (V_OC) of 0.86 V, a short circuit current density (J_SC) of 6.10 mA/cm², and a fill factor of 51% under AM 1.5G illumination at 100 mW/cm², which is the best results for fluorene and 4,7‐di‐2‐thienyl‐2,1,3‐benzothiadiazole copolymers and PC₆₁BM blend. The 1,8‐diiodooctane can work well to reduce the over‐aggregated phase structure in polymer solar cells. Our results suggest that the introducing high hydrophilic side chain into conjugated polymer donor materials can tune the aggregation structure and improve the solar cells performances. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40478.     

Synthesis of a terpolymer containing fluorene,side chain conjugated thiophene and benzothiadiazole and its applications in photovoltaic devices

A terpolymer (POTVTh‐8FO‐DBT) containing fluorene, side chain conjugated thiophene and 4,7‐dithieny‐2,1,3‐benzothiadiazole was synthesized by palladium‐catalyzed Suzuki coupling method. The polymer is soluble in common organic solvents. The thermal, absorption, and electrochemical properties of the polymer were examined. Photovoltaic properties of POTVTh‐8FO‐DBT were studied by fabricating the polymer solar cells (PSCs) based on POTVTh‐8FO‐DBT as donor and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC₆₁BM) as acceptor. With the weight ratio of POTVTh‐8FO‐DBT : PC₆₁BM of 1 : 1 and the active layer thickness of 80 nm, the power conversion efficiency (PCE) of the device reached 0.47% with V_oc = 0.61 V, J_sc = 1.61 mA/cm², and filled factor (FF) = 0.49 under the illumination of AM 1.5, 100 mW/cm². The results indicated that this polymer was promising donor candidates in the application of PSCs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A new series of random conjugated copolymers containing 3,4-diphenyl-maleimide and thiophene units for organic photovoltaic cell applications

A series of random conjugated copolymers (labeled PMLTQT, PMLT2T, and PMLT3T) consisting of 3,4-diphenyl-maleimide and various thiophene derivatives has been designed and synthesized via Stille cross-coupling for application in polymer solar cells. These copolymers were readily soluble in common organic solvents, thermally stable from 405 to 437 °C upon heating, and exhibited good absorption in the UV and visible regions from 300 to 650 nm. The intensities of the PL emission spectra of these copolymers in a solid film were dramatically quenched by the addition of 50 wt% [6,6]-phenyl C₆₁ butyric acid methyl ester (PC₆₁BM). Their electrochemical properties indicated that the highest occupied molecular orbital levels of these copolymers were in the range of ?5.63–5.73 eV, characteristic of better air stability and a high open-circuit voltage (V_oc) suitable for application to photovoltaic cells. Bulk heterojunction photovoltaic devices composed of an active layer of electron-donor copolymers blended with the electron acceptor PC₆₁BM or [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) at a weight ratio of 1:3 were investigated. The photovoltaic device containing PMLT3T and PC₇₁BM (1:3, w/w) as the active layer afforded the best performance among these copolymers, with a V_oc of 0.74 V, J_sc of 7.4 mA cm^?2 and a PCE of 1.20% under AM 1.5 G simulated solar light.     

Conjugated polymers with polar side chains in bulk heterojunction solar cell devices

Two polymers with polar side chains, namely poly[2,7‐(9,9‐dioctylfluorene)‐alt‐5,5‐(5',8'‐di‐2‐thienyl‐(2',3'‐bis(3''‐(2‐(2‐methoxyethoxy)ethoxy)phenyl)quinoxaline))] ( P1 ) and poly[2,7‐(9,9‐bis(2‐(2‐methoxyethoxy)ethyl)fluorene)‐alt‐5,5‐(5',8'‐di‐2‐thienyl‐(2',3'‐bis(3''‐(2‐(2‐methoxyethoxy)‐ethoxy)phenyl)quinoxaline))] ( P2 ), were synthesized for solar cell application. A series of bulk heterojunction solar cells were systematically fabricated and characterized by varying the electron‐acceptor materials, processing solvents and thickness of the active layer. The results show that P1 , with a higher molecular weight and good film‐forming properties, performed better. The best device showed an open circuit voltage of 0.87 V, a short circuit current of 6.81 mA cm^?2 and a power conversion efficiency of 2.74% with 1:4 polymer:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PCBM[70]) mixture using o‐dichlorobenzene (o‐DCB) as processing solvent. P2 on the other hand showed a poorer performance with chlorobenzene as processing solvent, but a much improved performance was obtained using o‐DCB instead. Thus, an open circuit voltage of 0.80 V, short circuit current of 6.21 mA cm^?2 and an overall power conversion efficiency of 2.22% were recorded for a polymer:PCBM[70] mixing ratio of 1:4. This is presumably due to the improvement of the morphology of the active layer using o‐DCB as processing solvent. © 2013 Society of Chemical Industry     

Polymer solar cells fabricated with 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene and alkyl-substituted thiophene-3-carboxylate-containing conjugated polymers: Effect of alkyl side-chain in thiophene-3-carboxylate monomer on the device performance

Four alkyl-substituted thiophene-3-carboxylate containing donor–acceptor (D–A) copolymers were designed, synthesized, and characterized. Thiophene-3-carboxylate was used as a weak electron acceptor unit in the copolymers to provide a deeper highest occupied molecular orbital (HOMO) level for obtaining a higher open-circuit voltage in polymer solar cells (PSCs). The resulting bulk heterojunction PSCs, made of the copolymers and [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁BM), exhibited different short circuit currents (J_SCs) and open-circuit voltages (V_OCs), depending on the length of alkyl side-chain in the thiophene-3-carboxylate unit. Among all fabricated photovoltaic (PV) devices, PC2:PC₇₁BM (1:1 wt. ratio) showed the highest efficiency with the highest J_SC of 10.5 mA/cm². Although PC5:PC₇₁BM (1:1) displayed the highest V_OC of 0.93 V, the device efficiency was observed to be poor, which is due to poor nanophase segregation. This comparison shows that the side-chain of thiophene carboxylate in these copolymers plays a very important role in the device efficiency.     

Tuning the photovoltaic performances of the terpolymers based on thiophene‐benzene‐thiophene via the modification of alkyl side chains

Three new random conjugated terpolymers based on thiophene‐2,5‐bis((2‐ ethylhexyl)oxy)benzene‐thiophene or thiophene‐2,5‐bis((2‐octyl)oxy)benzene‐ thiophene as electron‐donating units, diketopyrrolopyrrole (DPP) and 4,7‐dithien‐5‐yl‐2,1,3‐benzothiadiazole (DTBT) side group as electron‐withdrawing units have been designed and synthesized by Stille‐coupling reaction. All the terpolymers exhibit good thermal stability, broad absorption in the range of 300 to 800 nm. By tuning the alkyl side chains of the terpolymers, the absorption spectra, HOMO energy levels and photovoltaic properties of the terpolymers changed dramatically. A bulk heterojunction polymer solar cell fabricated from terpolymer GP2 and PC₆₁BM exhibited a promising power conversion efficiency of 3.31% without any processing additives. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42982.     

Synthesis of a soluble polythiophene copolymer with thiophene–vinylene conjugated side chain and its applications in photovoltaic devices

A new soluble polythiophene copolymer with thiophene‐vinylene conjugated side chain poly[3‐(5′‐octylthienylenevinyl) thiophene]‐thiophene (POTVTh‐Th) was successfully synthesized and characterized using NMR, UV‐visible spectroscopy, etc. To study the photovoltaic property of the copolymer, photovoltaic device of ITO/PEDOT:PSS/POTVTh‐Th:[6,6]‐phenyl C₆₁‐butyric acid methyl ester (PC₆₁BM) (weight ratio being 1 : 1)/LiF/Al was fabricated, in which POTVTh‐Th acted as the electron donor in the active layer. Under 100 mW/cm² AM 1.5G simulated solar emission, the open‐circuit voltage and the short‐circuit current density of the device were 0.58 V and 2.50 mA/cm², respectively. The power conversion efficiency and the fill factor of the photovoltaic device were evaluated to be 0.42% and 0.30. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Efficiency above 6% in poly(3‐hexylthiophene):phenyl‐C‐butyric acid methyl ester photovoltaics via simultaneous addition of poly(3‐hexylthiophene) based grafted graphene nanosheets and hydrophobic block copolymers

A combination of reduced graphene oxide (rGO) nanosheets grafted with regioregular poly(3‐hexylthiophene) (P3HT) (rGO‐g‐P3HT) and P3HT‐b‐polystyrene (PS) block copolymers was utilized to modify the morphology of P3HT:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) active layers in photovoltaic devices. Efficiencies greater than 6% were acquired after a mild thermal annealing. To this end, the assembling of P3HT homopolymers and P3HT‐b‐PS block copolymers onto rGO‐g‐P3HT nanosheets was investigated, showing that the copolymers were assembled from the P3HT side onto the rGO‐g‐P3HT nanosheets. Assembling of P3HT‐b‐PS block copolymers onto the rGO‐g‐P3HT nanosheets developed the net hole and electron highways for charge transport, thereby in addition to photoluminescence quenching the charge mobility (μ_h and μ_e) values increased considerably. The best charge mobilities were acquired for the P3HT₅₀₀₀₀:PC71BM:rGO‐g‐P3HT₅₀₀₀₀:P3HT₇₀₀₀‐b‐PS₁₀₀₀ system (μ_h = 1.9 × 10^?5 cm² V^–1 s^–1 and μ_e = 0.8 × 10^?4 cm² V^–1 s^–1). Thermal annealing conducted at 120 °C also further increased the hole and electron mobilities to 9.8 × 10^?4 and 2.7 × 10^?3 cm² V^–1 s^–1, respectively. The thermal annealing acted as a driving force for better assembly of the P3HT‐b‐PS copolymers onto the rGO‐g‐P3HT nanosheets. This phenomenon improved the short circuit current density, fill factor, open circuit voltage and power conversion efficiency parameters from 11.13 mA cm^?2, 0.63 V, 62% and 4.35% to 12.98 mA cm^?2, 0.69 V, 68% and 6.09%, respectively. © 2019 Society of Chemical Industry     

Fluorene‐based copolymers with donor–acceptor units on the side chain and main chain: Synthesis and application in polymer solar cells

Two narrow band gap fluorene‐based copolymers with donor–acceptor (D–A) structure on the polymer side chain and/or main chain are synthesized by Pd‐catalyzed Stille coupling reactions. The two copolymers have excellent thermal stability. The effects of D–A structure on the main and side chains on the absorption and electrochemical properties are studied. The copolymer PF‐BTh‐DBT with D–A structure both on the main and side chains has broader and stronger absorption and narrower band gap than the copolymer PF‐BTh with only a pendent D–A structure. The power conversion efficiency of the assembled solar cell using PF‐BTh‐DBT as donor and PC₇₁BM as acceptor is 1.6% with open‐circuit voltage (V_oc) 0.84 V under simulated AM 1.5 G solar irradiation (100 mW/cm²). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3276–3281, 2013     

Effects of thiophene units on substituted benzothiadiazole and benzodithiophene copolymers for photovoltaic applications

Two conjugated copolymers, poly{4,7-[5,6-bis(octyloxy)]benzo(c)(1,2,5)thiadiazole-alt-4,8-di(2-ethylhexyloxyl)benzo[1,2-b:3,4-b]dithiophene} ( P1 ) and poly(2-{5-[5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo(c)(1,2,5)thiadiazol-7-yl] thiophen-2-yl}-4,8-di(2-ethylhexyloxyl)benzo(1,2-b:3,4-b)dithiophene) ( P2 ), composed of benzodithiophene and 5,6-dioctyloxybenzothiadiazole derivatives with or without thiophene units were synthesized via a Stille cross-coupling polymerization reaction. These copolymers are promising for applications in bulk heterojunction solar cells because of their good solubility, proper thermal stability, moderate hole mobility, and low band gap. The photovoltaic properties of these copolymers were investigated on the basis of blends of the different polymer/(6,6)-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) weight ratios under AM1.5G illumination at 100 mW/cm². The device with indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)/ P2: PC₇₁BM (1 : 2 w/w)/Ca/Al gave a relatively better photovoltaic performance with a power conversion efficiency of 1.55%. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A copolymer based on benzo[1,2-b:4,5-b′]dithiophene and quinoxaline derivative for photovoltaic application

A D–A–D copolymer (PBDTQx) with a bandgap of 1.78 eV, containing alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) as donor and quinoxaline derivative (Qx) as acceptor, was synthesized by Stille coupling reaction. In order to study the photovoltaic property of PBDTQx, polymer solar cells (PSCs) were fabricated with PBDTQx as the electron donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM) as the electron acceptor. The power conversion efficiency (PCE) of PSC was 1.01% for an optimized PBDTQx: PC₆₁BM ratio of 1:5, under the illumination of AM 1.5, 100 mW/cm². The results indicated that PBDTQx was a promising donor candidate in the application of polymer solar cells.