Organic Polymer Solar Cells Research Articles

A New Benzodithiophene Based Donor-Acceptor π-Conjugated Polymer for Organic Solar Cells

A new benzodithiophene based donor-acceptor π-conjugated polymer (P1) is designed and explored as the photoactive donor for organic solar cells (OSCs). The synthesized donor polymer, P1 displays a wide absorption profile ranging from 300–750 nm with optical band gap of 1.61 eV and moderate ionization potential of −5.30 eV. It has good solubility in non-halogenated and halogenated organic solvents. Next, we fabricated OSCs with P1 by blending with PC71BM, the pristine polymer processed from chlorobenzene showed PCE of 2.79%. Upon addition of external additive diphenyl ether to the blend showed a dramatic improvement in PCE with maximum of 5.33%. DPE tailored the active layer morphology and showed two times higher PCE than pristine films. These results clearly indicate that the new polymer has a great potentiality for enhancing efficiency upon solvent additives, which will provide new routes for the development of new class of polymers for high-performance air-stable OSCs.

Determining the sequence and backbone structure of “semi-statistical” copolymers as donor–acceptor polymers in organic solar cells

Organic photovoltaics (OPVs) are attracting significant attention due to the growing demand for economically viable and renewable energy sources.

Narrow bandgap difluorobenzochalcogenadiazole-based polymers for high-performance organic thin-film transistors and polymer solar cells

A series of difluorobenzochalcogenadiazole-bithiophene copolymers are developed for high-performance organic semiconductors.

Utilizing Difluorinated Thiophene Units To Improve the Performance of Polymer Solar Cells

While there are numerous approaches to functionalize conjugated polymers for organic solar cells (OSCs), one widely adopted approach is fluorination. Of the many different locations for fluorination, one of the least studied is the conjugated linker which connects the donor and acceptor moieties; further, all existing reports primarily explore monofluorinated thiophene units. Herein, we synthesize and compare two conjugated polymers, HTAZ and dFT-HTAZ, which have different thiophene linkers. In HTAZ, a bare thiophene unit connects the donor and acceptor moieties, while dFT-HTAZ utilizes difluorinated thiophene (dFT) linkers. These polymers serve as the model system to explore the impact of dFT units in OSCs; additionally, this is the first publication to investigate polymers containing dFT units paired with non-fullerene acceptors. Compared to HTAZ, the incorporation of the dFT units maintained the optical properties while lowering the energy levels by ∼0.4 eV, which allowed for a much improved Voc value of ∼1 V. Importantly, when compared with the appropriate non-fullerene acceptor, dFT-HTAZ:ITIC-Th1 blends reached an efficiency of ∼10%, which is nearly 3× that of the nonfluorinated HTAZ. As most OSC polymers have thiophene linkers, using dFT units could serve as a proficient method to increase OSC performance in many polymer systems, especially those that do not have locations for functionalization on the acceptor moiety.

Optimization of PEDOT:PSS Hole Transport Layer Toward the Organic Solar Cells with High Fill Factor

We have investigated the effect of diluting treatment of poly (3,4-ethylenedioxythiophen e):poly (styrene sulfonate)(PEDOT:PSS) solution on the PEDOT:PSS films and the organic polymer solar cells based on poly [4,8-bis (5-(2-ethylhexyl) thiophen-2-yl) benzo [1,2-b;4,5-b0] dithiophene-co-3-fluorothieno [3,4-b] thiophene-2-carboxylate](PTB7-Th):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) using PEDOT:PSS polymer as the hole transport layer. The diluted PEDOT:PSS solution by water with 1:1.5 volume ratio was used to fabricate the hole transport layer in the organic solar cell, the fill factor and the shunt resistance of the solar cell can be significantly enhanced compared with the control cell, up to 64% and 949.03Ω·cm2, respectively.

New cyclopentadithiophene-based (X-DAD′AD)n conjugated polymers for organic solar cells

Five new donor-acceptor (X-DAD'AD)n type conjugated polymers have been synthesized using different X blocks based on carbazole, fluorene, silafluorene, benzodithiophene, and cyclopentadithiophene (CPDT). The strongly electron donating CPDT unit was used as a central D′ fragment to enhance intramolecular charge transfer interactions along the polymer backbone and reduce the bandgap of the resulting conjugated polymers. Apparently, the nature of the X block impacts the photophysical, morphological and optoelectronic properties of the designed polymers as well as their performance in bulk heterojunction solar cells. Fluorene-based copolymer P2 in combination with [70]PCBM delivered the best power conversion efficiency of 5.0% with a VOC of 0.78 V, a JSC of 11.1 mA/cm2 and a FF of 57%. Possibility for easy variation of the X and D′ blocks in the designed materials paves a way towards design of a variety of new materials for optoelectronic applications.

Synthesis and characterization of cyclic P3HT as a donor polymer for organic solar cells

ABSTRACTIn this study, cyclic poly(3‐hexylthiophene‐2,5‐diyl) (c‐P3HT) with a controlled Mn was synthesized by the intramolecular cyclization of α‐bromo‐ω‐ethynyl‐functionalized P3HT via the Sonogashira coupling reaction. The effect of the cyclic structure, which does not have terminal groups of polymers, on the photoelectric conversion characteristics was investigated in comparison to linear P3HT (l‐P3HT). c‐P3HT was successfully synthesized with Mn ≈ 17,000, dispersity ≈ 1.2, and regioregularity ≈ 99%. The hole mobility was determined to be 5.1 × 10−4 cm2 V−1 s−1 by time‐of‐flight (TOF) experiment. This was comparable to that of l‐P3HT of 5.6 × 10−4 cm2 V−1 s−1. Organic solar cell systems were fabricated with each polymer by blending them with [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM). The l‐P3HT:PC71BM system showed a dispersive TOF photocurrent profile for electron transport, whereas a nondispersive profile was observed for c‐P3HT:PC71BM. In addition, an amount of collected electrons in c‐P3HT:PC71BM was greater than that in l‐P3HT:PC71BM for TOF experiments. The photoelectric conversion characteristics were improved by using c‐P3HT rather than l‐P3HT (power conversion efficiency [PCE] = 4.05% vs 3.23%), reflecting the nondispersive transport and the improvement of electron collection. PCEs will be much improved by applying this cyclic concept to highly‐efficient OSC polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 266–271

2,2'-Bithiophene]-4,4'-dicarboxamide: a novel building block for semiconducting polymers.

A novel electron deficient building block [2,2′-bithiophene]-4,4′-dicarboxamide (BTDCA) was designed to lower the highest occupied molecular orbital (HOMO) energy level of polythiophenes in order to achieve a higher open circuit voltage (Voc) and thus a higher power conversion efficiency in polymer solar cells (PSCs). BTDCA dibromo monomers were conveniently synthesized in four steps, and were used to prepare three thiophene-based D-A polymers, P(BTDCA66-BT) (66BT), P(BTDCA44-BT) (44BT) and P(BTDCA44-TT) (44TT). All the polymers exhibited unipolar hole transport properties, exhibiting mobilities in the range of ∼10−4 to 10−2 cm2 V−1 s−1 with the highest hole mobility of up to 1.43 × 10−2 cm2 V−1 s−1 achieved for 44BT in bottom-gate bottom-contact organic thin film transistors (OTFTs). In PSCs, these polymers achieved high Voc's of 0.81–0.87 V when PCBM or ITIC was used as acceptor. When 44TT was used as donor and ITIC was used as acceptor, a power conversion efficiency (PCE) of up to 4.5% was obtained, a significant improvement when compared with the poly(3-hexylthiophene) (P3HT):ITIC devices, which showed the highest PCE of merely 0.92%.

Green Solvent Processed Conjugated Polymers for Organic Solar Cells: The Impact of Oligoethylene Glycol Side Chains

Green Solvent Processed Conjugated Polymers for Organic Solar Cells: The Impact of Oligoethylene Glycol Side Chains

Quantitative structure-property relationship modeling of the C60 fullerene derivatives as electron acceptors of polymer solar cells: Elucidating the functional groups critical for device performance

Using the GUSAR 2013 program, we have performed a quantitative analysis of the “structure–power conversion efficiency (PCE)” on the series of 100 methano[60]fullerenes previously tested as acceptor components of bulk-heterojunction polymer organic solar cells (PSCs) utilizing the same donor polymer, viz. poly(3-hexylthiophene). Based on the MNA and QNA descriptors and self-consistent regression implemented in the program, six statistically significant consensus models for predicting the PCE values of the methano[60]fullerene-based PSCs have been constructed. The structural fragments of the fullerene compounds leading to an increase in the device performances are determined. Based on these structural descriptors, we have designed the three methano[60]fullerenes included in the training sets and characterized by poor optoelectrical properties is performed. As a result, two new compounds with potentially moderate efficiency have been proposed. This result opens opportunities of using the GUSAR 2013 program for modeling of the “structure–PCE” relationship for diverse compounds (not only fullerene derivatives).

Imide‐Functionalized Polymer Semiconductors

Imide-functionalized π-conjugated polymer semiconductors have received a great deal of interest owing to their unique physicochemical properties and optoelectronic characteristics, including excellent solubility, highly planar backbones, widely tunable band gaps and energy levels of frontier molecular orbitals, and good film morphology. The organic electronics community has witnessed rapid expansion of the materials library and remarkable improvement in device performance recently. This review summarizes the development of imide-functionalized polymer semiconductors as well as their device performance in organic thin-film transistors and polymer solar cells, mainly achieved in the past three years. The materials mainly cover naphthalene diimide, perylene diimide, and bithiophene imide, and other imide-based polymer semiconductors are also discussed. The perspective offers our insights for developing new imide-functionalized building blocks and polymer semiconductors with optimized optoelectronic properties. We hope that this review will generate more research interest in the community to realize further improved device performance by developing new imide-functionalized polymer semiconductors.

Effects of inserting keto-functionalized side-chains instead of imide-functionalized side-chain on the pyrrole backbone of 2,5-bis(2-thienyl)pyrrole-based polymers for organic solar cells

A 2,5-bis(2-thienyl)pyrrole (TPT)-based new monomer unit incorporating the electron-withdrawing 1-decanone (ketone) at the 3- and 4-positions of the pyrrole unit of TPT was prepared. The resulting keto-functionalized TPT unit (≈TPTK) was polymerized with distannyl derivatives of 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (BDTT), 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT), and 3,6-bis(thiophen-2-yl)-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DKPP), to obtain three new polymers (P(BDTT-TPTK), P(DTBT-TPTK) and P(DKPP-TPTK)), respectively. The photophysical, electrochemical, and energy conversion efficiency of the TPTK-based polymers were thoroughly studied and compared with those of structurally similar polymers (P(BDTT-TPTI), P(DTBT-TPTI), and P(DKPP-TPTI)) incorporating an imide-functionalized TPT unit (≈ TPTI). Overall, the TPTK-based polymers showed a higher band-gap (Eg ≈ 2.42 eV, 1.92 eV, and 1.42 eV), deeper highest occupied molecular orbital (HOMO ≈ −5.58 eV, −5.48 eV, and −5.31 eV, respectively) energy levels and lower carrier mobilities than those of the corresponding TPTI-based polymers. These combined effects led to relatively poor solar to electrical energy conversion efficiency for TPTK-based polymers compared to those of TPTI-based polymers.

Near-infrared non-fullerene acceptors based on dithienyl[1,2-b:4,5-b’]benzodithiophene core for high performance PTB7-Th-based polymer solar cells

Two non-fullerene electron acceptors (BT-SFIC and BT-FIC) bearing a dithienyl[1,2-b:4,5-b’]benzodithiophene core were designed and synthesized. Due to the strong electron-withdrawing ability of fluorine atoms, these two non-fullerene acceptors both show near-infrared absorption around 900 nm, with a narrow bandgap of 1.44 and 1.39 eV for BT-SFIC and BT-FIC, respectively. BT-SFIC and BT-FIC have complementary absorption and matched energy level with PTB7-Th. PSCs based on PTB7-Th donor and these two acceptors both show good charge dissociation and collection, small charge recombination and good active layer morphology. However, BT-FIC bearing much more fluorine have much higher electron mobility. And the PSCs based on PTB7-Th: BT-FIC gives a maximum PCE of 10.10% with a VOC of 0.73 eV, a JSC of 21.28 mA cm−2 and an FF of 65%, which is among in the high-performance polymer organic solar cells based on PTB7-Th.

Data for: Simply Tuning the Electron Deficient Units to Achieve P- and N-type Conjugated Polymers for Organic Solar Cells

Abstract D-A strategy and noncovalent conformational locks (NCLs) have been employed as important tools to construct highly performing conjugated polymers (CPs). In this work, a donor (D) unit (E)-1,2-diethoxy-1,2-bis(5-(trimethylstannyl)thieno[3,2-b]thiophen-2-yl)ethene (FS) with S⋯O NCLs was copolymerized with four different acceptor (A) units. Upon changing the electron deficient properties of the A unit, the electronic properties of the CPs were successfully tuned to afford two p-type CPs and two n-type CPs. The optical absorption, electrochemical properties, molecular geometries, photovoltaic properties, charge transport characteristics, and morphology of these polymers and corresponding devices were systematically investigated. P-type polymer PffBT2T-FS and n-type polymer PPDI-FS based devices achieved PCEs as high as 5.03% and 3.23%, respectively. This contribution provides a synthetic strategy for constructing novel high-performance CPs.

Simply tuning the electron deficient units to achieve P[sbnd] and N-type conjugated polymers for organic solar cells

D-A strategy and noncovalent conformational locks (NCLs) have been employed as important tools to construct highly performing conjugated polymers (CPs). In this work, a donor (D) unit (E)-1,2-diethoxy-1,2-bis(5-(trimethylstannyl)thieno[3,2-b]thiophen-2-yl)ethene (FS) with S⋯O NCLs was copolymerized with four different acceptor (A) units. Upon changing the electron deficient properties of the A unit, the electronic properties of the CPs were successfully tuned to afford two p-type CPs and two n-type CPs. The optical absorption, electrochemical properties, molecular geometries, photovoltaic properties, charge transport characteristics, and morphology of these polymers and corresponding devices were systematically investigated. P-type polymer PffBT2T-FS and n-type polymer PPDI-FS based devices achieved PCEs as high as 5.03% and 3.23%, respectively. This contribution provides a synthetic strategy for constructing novel high-performance CPs.

Novel D-A type dyes based on BODIPY for solution processed organic polymer solar cells

Boron dipyrromethene (BODIPY) derivatives have good optoelectronic properties and thermal stability. However, it is rarely for such materials to use in bulk heterojunction (BHJ) organic solar cell. In this study, a variety of donor-acceptor (D-A) type boron dipyrromethene (BODIPY) based dyes were designed and synthesized for polymer solar cells (PSCs), namely BDH1-4. Thermal stability, photochemical properties, charge transport and BHJ morphology were investigated to elucidate factors affecting the photovoltaic performance in this class of polymers. These BDHs exhibit fine solubility in conventional solvents, good thermal stability, excellent panchromatic absorption in solution and in film. Furthermore, the absorption wavelength of BDH1-4 covers full color absorption in the range of 300–800 nm and has a relatively low HOMO level from −5.01 to −5.66 eV. Among them, BDH4/PC71BM based PSCs exhibit highest power conversion efficiency (PCE) of 3.69% with a Jsc of 9.92 mA cm−2, a Voc of 0.63 V and a FF of 59.1%.

Crystalline Conjugated Polymers for Organic Solar Cells: From Donor, Acceptor to Single-Component.

Organic solar cells have made rapid progress in the last two decades due to the innovation of conjugated materials and photovoltaic devices. Microphase separation that connects with materials and devices plays a crucial role in the charge generation process. In this account, we summary our recent works of developing new crystalline conjugated polymers to control the microphase separation in thin films in order to realize high performance in solar cells, including crystalline diketopyrrolopyrrole-based donor polymers, perylene bisimide-based electron acceptors, and "double-cable" conjugated polymers that contain covalently-linked crystalline donor and acceptor in one material for single-component organic solar cells.

Isoindigo-based conjugated polymer for high-performance organic solar cell with a high VOC of 1.06 V as processed from non-halogenated solvent

The fabrication of organic solar cells using non-halogenated solvents have been recently explored in order to replace conventionally used halogenated solvents that cause environmental, health and safety problems. For achieving highly efficient organic solar cells using non-halogenated solvents, conjugated polymer should be designed and developed to afford high solubility in non-halogenated solvent and desirable photovoltaic properties in finally fabricated devices. Here, we demonstrated that an isoindigo-based copolymer, PiI2fT, composed of isoindigo with 2-decyltetradecane and bithiophene with fluorination is a promising polymer for organic solar cells using eco-friendly non-halogenated solvent. We found that the introduction of fluorine atom in conjugated polymer affords improved photophysical properties including intense light absorption, lowering of the highest occupied molecular orbital energy level and increase of dipole moment, while the introduction of bulk alkyl chain in the polymer may enhance the solubility in organic solvents. When solar cells were fabricated from using o-xylene and diphenyl ether as solvent and additive, PiI2fT polymer exhibited a high PCE of 8.80% with an open-circuit voltage of 1.06 V.

Synthesis and characterization of the fluorinated thieno[3,4-c]pyrrole-4,6-dione-based donor-acceptor polymers for organic solar cells

A new wide bandgap polymer (PC8TPD-F) has been synthesized via the Stille cross-coupling reaction between fluorine-substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) and 4,8-bis(5-hexylthiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene (BDTT). For structural comparison, the nonfluorinated TPD-based BDTT polymer (PC8TPD) was also synthesized with the same polymerization. The number average molecular weights (Mn) of PC8TPD and PC8TPD-F were found to be 47,000 g/mol (Đ = 2.1) and 52,000 g/mol (Đ = 1.8) respectively. The HOMO levels of PC8TPD and PC8TPD-F were determined to be −5.56 and–5.65 eV respectively. The inclusion of the fluorinated TPD unit lowers the polymer's HOMO level. The SCLC mobilities of PC8TPD and PC8TPD-F were determined to be 1.5 × 10−4 and 2.1 × 10−4 cm2/V respectively. Polymer solar cell devices prepared with PC8TPD and PC8TPD-F as their active layers were found to exhibit power conversion efficiencies of 4.26% and 6.80% with open circuit voltages of 0.90 V and 0.95 V respectively.

Mechanically robust stretchable organic optoelectronic devices built using a simple and universal stencil-pattern transferring technology

Stretchable electronic and optoelectronic devices based on controllable ordered buckling structures exhibit superior mechanical stability by retaining their buckling profile without distortion in repeated stretch-release cycles. However, a simple and universal technology to introduce ordered buckling structures into stretchable devices remains a real challenge. Here, a simple and general stencil-pattern transferring technology was applied to stretchable organic light-emitting devices (SOLEDs) and polymer solar cells (SPSCs) to realize an ordered buckling profile. To the best of our knowledge, both the SOLEDs and SPSCs with periodic buckles exhibited the highest mechanical robustness by operating with small performance variations after 20,000 and 12,000 stretch-release cycles between 0% and 20% tensile strain, respectively. Notably, in this work, periodic-buckled structures were introduced into SPSCs for the first time, with the number of stretch-release cycles for the SPSCs improved by two orders of magnitude compared to that for previously reported random-buckled stretchable organic solar cells. The simple method used in this work provides a universal solution for low-cost and high-performance stretchable electronic and optoelectronic devices and promotes the commercial development of stretchable devices in wearable electronics.