Materials For Polymer Solar Cells Research Articles

Metal oxide-embedded carbon-based materials for polymer solar cells and X-ray detectors.

This study examines the effects of hybrid nanoparticles made of NiO@rGO (reduced graphene oxide) and NiO@CNT (carbon nanotubes) on PCDTBT and PCBM active layers in glass/ITO/HTL/active-layer/LiF/Al structured bulk heterojunction (BHJ) polymer solar cells (PSCs) and X-ray photodetectors. These hybrid nanoparticles were used to create BHJ solar cells and photodetectors, and microscopic research was conducted to determine how they affect the structure of the devices. The findings show that compared to conventional matrices, the active layers with NiO@rGO and NiO@CNT incorporation have increased the charge carrier capacities and exciton dissociation properties. In order to assess their impact on the characteristics of charge transport, various weight ratios of these hybrid nanoparticles dispersed in polymer junctions are being investigated. Notably, compared to the pure PCDTBT:PCBM active layer (power conversion efficiency (PCE) = 4.35%), the NiO@CNT device has the highest PCE = 6.42% which, among the tested configurations, demonstrates its superior performance in converting sunlight into electricity. Among the tested X-ray detector materials, "NiO@CNT" achieves the best performance with a sensitivity of 1.92 mA Gy-1 cm-2. Through improved interfacial behaviors and effective charge transport, this work highlights the potential of these cutting-edge hybrid nanoparticles to enhance the performance of organic electronic devices.

Effects of Different Lengths of Oligo (Ethylene Glycol) Side Chains on the Electrochromic and Photovoltaic Properties of Benzothiadiazole-Based Donor-Acceptor Conjugated Polymers.

In recent years, donor-acceptor (D-A)-type conjugated polymers have been widely used in the field of organic solar cells (OSCs) and electrochromism (EC). Considering the poor solubility of D-A conjugated polymers, the solvents used in material processing and related device preparation are mostly toxic halogenated solvents, which have become the biggest obstacle to the future commercial process of the OSC and EC field. Herein, we designed and synthesized three novel D-A conjugated polymers, PBDT1-DTBF, PBDT2-DTBF, and PBDT3-DTBF, by introducing polar oligo (ethylene glycol) (OEG) side chains of different lengths in the donor unit benzodithiophene (BDT) as side chain modification. Studies on solubility, optics, electrochemical, photovoltaic and electrochromic properties are conducted, and the influence of the introduction of OEG side chains on its basic properties is also discussed. Studies on solubility and electrochromic properties show unusual trends that need further research. However, since PBDT-DTBF-class polymers and acceptor IT-4F failed to form proper morphology under the low-boiling point solvent THF solvent processing, the photovoltaic performance of prepared devices is not ideal. However, films with THF as processing solvent showed relatively desirable electrochromic properties and films cast from THF display higher CE than CB as the solvent. Therefore, this class of polymers has application feasibility for green solvent processing in the OSC and EC fields. The research provides an idea for the design of green solvent-processable polymer solar cell materials in the future and a meaningful exploration of the application of green solvents in the field of electrochromism.

Fluorine‐Substituted π‐Bridge through a Simple Method for Efficient Polymer Donor

Herein, a novel fluorinated conjugated polymer, PM7‐F, as the donor material for polymer solar cells (PSCs) is developed. In contrast to previously reported synthetic methods for 3‐fluorothiophene, a crucial intermediate, 3‐fluoro‐2‐iodothiophene, is utilized, to shorten the synthetic route and ensure lower synthetic costs via a simple approach. The effects of fluorine substituent on the π‐bridge unit are systematically investigated. PM7‐F displays great planarity and a nearly linear backbone via its strong intramolecular noncovalent conformation locks. Due to the strong noncovalent contacts of F–S, F–π, and F–Cl, as well as the large dipole moment of carbon–fluorine (C–F), the fluorinated polymer PM7‐F possesses redshifted absorption, a much deeper highest occupied molecular orbital level (−5.65 eV), better crystallinity, enhanced nanoscale morphology, efficient charge transport properties, and reduced recombination behaviors than its nonfluorine counterpart. As a result, the PM7‐F:ITIC‐based PSCs exhibit a remarkable power conversion efficiency of 13.46% with a open‐circuit voltage of 0.94 V, a short‐circuit current of 20.79 mA cm−2, and an fill factor of 68.87%. Herein, it is indicated that fluorination π‐bridge provided a feasible approach to obtain low‐cost and high‐efficiency polymer donors.

Novel conjugated polymers based on cyclopenta[c]thiophene-4,6(5H)-dione for efficient polymer solar cells

A series of polymers based on indandione derivatives, TIND-HT-BDT, TIND-HT-BDTF, TIND-DHT-BDT, and TIND-DHT-BDTF, were synthesized as donor materials for polymer solar cells (PSCs). The polymers have a typical donor-acceptor configuration, where TIND-HT (5-((5-hexylthiophen-2-yl)methylene)-4H-cyclopenta[c]thiophene-4,6(5H)-dione) and TIND-DHT (5-((4,5-dihexylthiophen-2-yl)methylene)-4H-cyclopenta[c]thiophene-4,6(5H)-dione) are the electron acceptor units, while benzodithiophene (BDT) or fluorinated benzodithiophene (BDTF) are the electron donor units. Non-fullerene inverted-type PSCs with a configuration of ITO/ZnO/polymer:Y6BO/MoO3/Ag devices based on polymers as the donor and Y6BO as the acceptor were fabricated. The best power conversion efficiency (PCE) of 11.1% was achieved using the inverted-type PSCs based on TIND-DHT-BDTF with an open-circuit voltage (Voc) of 0.82 V and short-circuit current density (Jsc) of 22.6 mA/cm2. This study provides insights into novel donor materials for non-fullerene PSCs.

Synthesis of a Low-Cost Thiophene-Indoloquinoxaline Polymer Donor and Its Application to Polymer Solar Cells.

A simple wide-bandgap conjugated polymer based on indoloquinoxaline unit (PIQ) has been newly designed and synthesized via cheap and commercially available starting materials. The basic physicochemical properties of the PIQ have been investigated. PIQ possesses a broad and strong absorption band in the wavelength range of 400~660 nm with a bandgap of 1.80 eV and lower-lying highest occupied molecular orbital energy level of −5.58 eV. Polymer solar cells based on PIQ and popular acceptor Y6 blend display a preliminarily optimized power conversion efficiency of 6.4%. The results demonstrate indoloquinoxaline is a promising building unit for designing polymer donor materials for polymer solar cells.

Toward the Rational Design of Organic Solar Photovoltaics: Application of Molecular Structure Methods to Donor Polymers.

Conjugated polymers are promising candidates in the design of polymer solar cell materials with suitable electronic properties. Recent studies show that the use of different functional groups as side chain in thiophene-based polymers changes the electronic and conformation structures. Here we design new thiophene-based molecules by replacing the hydrogen attached to the backbone of P3MT with electron-donating and electron-withdrawing groups. We then calculate the HOMO, LUMO, and HOMO–LUMO energy gap to quantify the theoretical merit of the new polymers as solar absorbers and their inter-ring torsional potential to understand their suitability to link together in high conductivity, extended conjugated systems. Calculations are done with first-principles density functional theory (DFT), implemented using B3LYP with dispersion function and 6-31G(d,p) as basis set. Our results show that the HOMO–LUMO gap is sensibly lowered by donating groups and we found that the substitution of the hydrogen with −NH2, and −F gives an energy gap lower than the energy gap of P3MT. The lowest energy gap was found when substituting with −NH2. Electron-withdrawing groups lower the HOMO, with the overall lowest found when −NO2 is used. −COCl, −CONH2, and −Cl give a steric hindrance greater than that of PTB7, which is set as reference. Our calculations show a possible approach to the rational design of donor materials when substituents are inserted systematically in a generic oligomer.

Ultrasonically Processed WSe2 Nanosheets Blended Bulk Heterojunction Active Layer for High-Performance Polymer Solar Cells and X-ray Detectors.

Two-dimensional (2D) tungsten diselenide (WSe2) has attracted considerable attention in the field of photovoltaic devices owing to its excellent structure and photoelectric properties, such as ordered 2D network structure, high electrical conductivity, and high mobility. For this test, we firstly prepared different sizes (NS1–NS3) of WSe2 nanosheets (NSs) through the ultrasonication method and characterized their structures using the field emission scanning electron microscope (FE-SEM), Raman spectroscopy, and X-ray powder diffraction. Moreover, we investigated the photovoltaic performance of polymer solar cells based on 5,7-Bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione(PBDB-T):(6,6)-phenyl-C71 butyric acid methyl ester (PCBM) with different WSe2 NSs as the active layer. The fabricated PBDB-T:PCBM active layer with the addition of NS2 WSe2 NSs (1.5 wt%) exhibited an improved power conversion efficiency (PCE) of 9.2%, which is higher than the pure and NS1 and NS3 WSe2 blended active layer-encompassing devices. The improved PCE is attributed to the synergic enhancement of exciton dissociation and an improvement in the charge mobility through the modified active layer for polymer solar cells. Furthermore, the highest sensitivity of 2.97 mA/Gy·cm2 was achieved for the NS2 WSe2 NSs blended active layer detected by X-ray exposure over the pure polymer, and with the NS1 and NS2 WSe2 blended active layer. These results led to the use of transition metal dichalcogenide materials in polymer solar cells and X-ray detectors.

Core effect on indacenodithieno[3,2-b]thiophene dimer based small molecule acceptors for non-fullerene polymer solar cells

Dimerization is a widely adopted approach to construct electron accepting materials for polymer solar cells (PSCs). Fullerene dimers were extensively explored with improved structural stability and perylene-diimide (PDI) dimers prevented the formation of undesired large crystals. However, dimers of indacenodithieno[3,2-b]thiophene (IDTT) chromophores have yet not been reported despite the great success in non-fullerene small molecule acceptors (NF-SMAs) such as ITIC. In this work, we designed and synthesized three IDTT dimers with conjugated cores or not and explored the core effect of introducing flexible dithiophene or rigid thienothiophene as linkage group. All the three IDTT dimers were found to be poorly crystallized and functional PSCs devices containing each of these dimers were successfully fabricated paring with donor polymer PBDB-T. The introduction of electron donating linkages raise energy levels of the dimers hence increased the open circuit voltages. Thienothiophene was found to be a more suitable linkage unit than dithiophene but the highest power conversion efficiency of 6.01% was recorded in devices based on dimer dIDTT without the linkage units. This work demonstrated the possibility of using IDTT chromophore to construct dimer NF-SMAs and revealed insights of core effect on their photovoltaic performance.

An alcohol-soluble small molecule as efficient cathode interfacial layer materials for polymer solar cells

Abstract Interface modification makes an important contribution to improving the optoelectronic performance and stability of polymer solar cells (PSCs). Here, the hexamethylenetetramine (C6H12N4) was successfully introduced into PSCs as cathode interface layers (CILs) using environmental-friendly methanol as solvent. Compared to the PSCs without CILs, the open circuit voltage (VOC) and short-circuit current density (JSC) of the device with C6H12N4 CILs was increased from 0.44 V to 12.73 mA cm−2 to 0.77 V and 15.89 mA cm−2, respectively. More importantly, under the same experimental conditions, the optimal power conversion efficiency (PCE) of the device with C6H12N4 CILs was improved to 7.79%, which is 185% higher than that of the device without C6H12N4 CILs (2.73%). We found that the active layer PTB7-Th:PC71BM showed a smoother interface morphology and better hydrophilicity after insertion of CILs, which facilitated enhance the physical contact between active layers and cathode as well as electron extraction and transport. The results show that the introduction of C6H12N4 as CILs provides an effective method for preparing high-performance PSCs.

Comparative study of the optoelectronic properties of diketopyrrolopyrrole based polymers obtained by direct C-H arylation

Donor–acceptor (D-A) type of new constituted diketopyrrolopyrrole-based polymers, PDPP-EDOT (poly A), PDPP-TP (poly B), and PDPP-EBTE (poly C), were synthesized by one-pot direct C–H heteroarylation polymerization methodology supported by Pd(OAc)2/Bu4NBr catalytic system. C–H heteroarylation coupling of highly selective sites avoided the difficulty of the synthesis using organometallic reagent and gave highly pure polymers in good yields. The targeted polymers were evaluated using NMR, TGA, DSC, UV–VIS absorption, GPC, and electrochemical cyclic voltammetry. The polymers are soluble in most of organic solvents, and TGA studies show their high thermally stability. Polymers bandgaps are tuned by alternative copolymerizing with different electron-donating and/or electron-withdrawing units. UV–VIS absorption spectra demonstrated that the polymers show excellent light absorption, with narrow optical bandgaps, around 1.20 eV, confirmed by cyclic voltammetry parameters. All of these promising properties indicated that they might be excellent polymeric materials for polymer solar cells, organic field effect transistors, and so on.

Donor−acceptor−donor (D-A-D) structural monomers as donor materials in polymer solar cells: a DFT/TDDFT approach

ABSTRACT Density functional theory (DFT) and time-dependent DFT (TD-DFT) are used to investigate the ground- and excited-state properties of donor-acceptor–donor (D-A-D) monomers based on 3,6-carbazole (CB) combined with various-conjugated benzothiazole derivatives, using B3LYP and the 6–311 G basis set. To create nine D-A-D monomers for this investigation, nine (9) distinct acceptors were inserted at the C3 and C6 positions of carbazole. The impact of various electron-donor groups on structural, electrical, and optoelectronic properties is investigated. Our technique for developing novel donor monomers provides a theoretical framework for further optimizing the photovoltaic device’s electrical, optical, and efficiency features. The HOMO and LUMO energies, bandgap, excited state, exciton binding energy, open-circuit voltage (VOC) and absorption spectra were calculated. Our findings indicate that CB-TDP-CB and CB-SDP-CB monomers have an appropriate electronic structure for polymer solar cells.

Comparative study of charge characteristics in PCPDTBT:fullerenes solar cells

• Spectral signal of PCPDTBT + species was obtained by spectroelectrochemistry. • Fullerene downwards shifts the HOMO level of PCPDTBT + near the D-A interface. • Fullerene promotes hole transport from near the D-A interface to polymer bulk phase. • Charge charateristics in PCPDTBT:fullerene solar cells were studied. PCPDTBT is a representative donor material for polymer solar cells, and the performance of PCPDTBT-based devices depends on the type of acceptors. To study the effect of fullerene structure on the performance of PCPDTBT-based device, the correlations among morphology, optical and electrical properties of photovoltaic devices were analyzed. The results showed that PCPDTBT:PC 71 BM had pronounced crystal order and phase separation comparing to that of PCPDTBT:PC 61 BM, which could be helpful for charge transport. Furthermore, we find the HOMO energy level of PCPDTBT + near the donor–acceptor interface was down-shifted due to interaction between donor and acceptor. The bended energy level at the interface could facilitate the hole transport from near the donor–acceptor interface to the bulk-phase of polymer, and thus reducing the charge recombination at the interface. Impedance test demonstrated that PCPDTBT:PC 71 BM device had smaller leakage current and better carrier transport, so that it showed higher power conversion efficiency than PCPDTBT:PC 61 BM device.

Novel bis-nitrile grafted [6]Helicenes through a photochemical pathway: Chiroptical and photophysical properties

New suitably nitrile grafted [6]Helicene derivatives have been synthesized, in 36%-54% over all yields, through a UV-light photochemical pathway making use of inexpensive materials and mild experimental conditions. The target hexacylic helicenes have been characterized by 1H and 13C NMR and FT-IR spectroscopies. The enantiomeric separation of these helical compounds was accomplished by chiral HPLC leading to (P)- and (M)-enantiomers with high optical purity (94.3–100% ee) demonstrating a large optical rotatory dispersion and significant electronic circular dichroism (ECD) signals. UV–vis absorption and photoluminescence of these helical compounds have been evaluated showing a notable behavior and a strong fluorescence in the blue region of the visible spectrum making them promising candidates for applications in electronic and optoelectronic devices. Their electrochemical behavior was also experimentally examined revealing an important charge transfer interaction owing to their π-conjugated electronic system. These helicenes were found to be potential donor materials for polymer solar cells, with broad electrochemical band gap in the range of 2.63–2.80 eV.

VOC enhancement of thienobenzofuran and benzotriazole backboned photovoltaic polymer by side chain sulfuration or fluoridation

In this work, four wide-bandgap (WBG) conjugated polymers based on asymmetrical building block thieno [2,3f]benzofuran (TBF) and fluorobenzotriazole (BZ), are synthesized and applied as donor materials in polymer solar cells (PSCs). The effect of conjugated side chains (alkylthiothiophenyl, alkylthiophenyl, alkylphenyl and fluoroalkoxyphenyl) on the optical absorption, electrochemical and photovoltaic properties are investigated in detail. These polymers exhibit similar properties, strong absorption from 300 to 650 nm with wide bandgaps ranging from 1.87 to 1.96 eV, excellent thermal stability, the high and balanced carrier mobility. Notably, the open-circuit voltages (VOC) of PTSDO-BZ increases by 0.16 V compared with PTDO-BZ. Similarly, larger VOC changes have also occurred in PPEH-BZ and PPFOEH-BZ comparation. The enhanced VOC can be ascribed to the low-lying highest occupied molecular orbital (HOMO) energy level by incorporating sulfur and fluorine substituents on the conjugated side chains. The as-cast devices of PTSDO-BZ:ITIC exhibit the highest power conversion efficiency (PCE) of 8.66%, with a VOC of 0.88 V, a short-circuit current density (JSC) of 15.06 mA cm−2, and a fill factor (FF) of 65.12%. The results indicate that the modification of the side chains of the TBF unit can effectively lower the HOMO energy levels and thereby obtaining high VOC.

Recent advances on aromatic-diimide based cathode interfacial materials for polymer solar cells

As an emerging photovoltaic technology, polymer solar cells (PSCs) have attracted broad interest for both academic and industry communities due to their outstanding advantages, such as lightweight, low cost and easy to process in large areas. In recent years, the power conversion efficiency of PSCs has been improved rapidly, exceeding 17% for the state-of-the-art devices. For device optimization, it has been demonstrated that the efficiency and stability can be significantly improved by constructing efficient organic cathode interfacial materials. Specially, aromatic-diimide based cathode interfacial materials have attracted much attention due to their advantages of excellent electron transport, easily chemical modification and suitable energy levels. In this review, along with the briefly introduction on the basic functions of cathode interlayer, recent progress of cathode interlayer based on perylene diimides and naphthalene diimides was summarized. At last, the perspective and challenge were proposed according to the requirements of practical application.

Optimization of Graphene Quantum Dots as Doping Materials in Polymer Solar Cells

Optimization of Graphene Quantum Dots as Doping Materials in Polymer Solar Cells

Nonhalogenated-Solvent-Processed Efficient Polymer Solar Cells Enabled by Medium-Band-Gap A-π-D-π-A Small-Molecule Acceptors Based on a 6,12-Dihydro-diindolo[1,2-b:10,20-e]pyrazine Unit.

In this contribution, a series of A-π-D-π-A small molecules (SMs), IPY-T-IC, IPY-T-ICCl, and IPY-T-ICF, containing the central donor unit (D) of 6,12-dihydro-diindolo[1,2-b:10,20-e]pyrazine (IPY), the π-conjugated bridge of thiophene, and the end-accepting group (A) of 3-(dic yanomethylidene)indol-1-one, 5,6-dichloro-3-(dicyanomethylidene)indol-1-one, or 5,6-difluoro-3-(dicyanomethylene)indol-1-one, were developed, characterized, and employed as the acceptor materials for polymer solar cells (PSCs). Influences of the different end-accepting groups on thermal properties, spectral absorption, energy levels, photovoltaic performance, and film morphology of these small-molecule acceptors (SMAs) were investigated in detail. These SMAs exhibit an excellent thermal stability and strong crystallization. The absorption spectra of these SMs mainly locate the wavelength between 400 and 700 nm, associated with the optical band gaps in the range of 1.75-1.90 eV. Compared with nonhalogenated IPY-T-IC, the halogenated SMAs IPY-T-ICCl and IPY-T-ICF present better absorption abilities, wider absorption region, and downshifted highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels. With regard to the complementary spectral absorption and matched HOMO/LUMO levels, PTB7-Th as a low-band gap polymer was chosen to be an electron donor to pair with these SMAs for fabricating bulk-heterojuntion PSCs. Under optimized conditions, among these SMAs, the PTB7-Th:IPY-T-IC-based PSC processed from a halogenated solvent system (chlorobenzene + 1-chloronaphthalene) delivers the best power conversion efficiency (PCE) of 7.32%, mainly because of more complementary spectral absorption, upper-lying LUMO level, higher and balanced carrier mobility, more efficiently suppressed trap-assisted recombination, better charge collection property, and blend morphology. Encouragingly, an improved PCE of up to 7.68% is achieved when the IPY-T-IC-based solar cell was processed from a nonhalogenated solvent system (o-xylene + 2-methylnaphthalene). In view of the large band gap of these IPY-based SMAs, the PCE of over 7.5% is notable and attractive for the related community. Our study argues that the IPY moiety is a potential electron-donating building moiety to develop medium-band-gap high-performance A-π-D-π-A SMAs for nonhalogenated-solvent-processed photovoltaic devices.

Enhanced JSC of P3HT-based non-fullerene polymer solar cells by modulating aggregation effect of P3HT in solution state

Abstract Poly(3-hexylthiophene) (P3HT) is a broadly used donor material for polymer solar cells (PSCs) due to its simple molecular structure and low production cost. In recent years, the P3HT-based non-fullerene PSCs have been extensively studied as the rapid development of the non-fullerene small molecular acceptors (NFSMAs). However, the active layers based on the P3HT and NFSMAs blend usually exhibit unfavorable phase separation morphologies, resulting in relatively low short-circuit currents (JSCs) and power conversion efficiencies (PCEs) of the corresponding PSC devices. Herein, we utilized the chloroform (CF)/anisole solvent mixture to adjust the aggregation effect of P3HT in solution state to optimize the phase separation morphology of the active layers. As a result, the combination of CF, anisole, and 1,8-diiodooctane (DIO) affords an enhanced JSC of 14.23 mA cm−2 for a P3HT:IEICO-based PSC.

High-performance conjugated polymer donor materials for polymer solar cells with narrow-bandgap nonfullerene acceptors

The state-of-the-art conjugated polymer donor materials for high-performance polymer solar cells based on narrow-bandgap nonfullerene acceptors are summarized and discussed.

A novel alkylsilyl-fused copolymer-based non-fullerene solar cell with over 12% efficiency

A new alkylsilyl-fused copolymer PBDS-TZ unit was developed as donor material for polymer solar cells. When blended with IT-4F, an appropriate micromorphology with vertical component distribution in active layer was obtained. A notably PCE of 12.01% with a high FF of 73.1% and JSC of 20.45 mA cm−2 for the devices.