P3HT Donor Research Articles

Acceptor molecules with Carbon–Carbon singly bonded central and terminal units for efficient P3HT-based organic solar cells

Herein, we synthesized two small molecules named as 4TBTCN and 6TBTCN with strongly electron-rich 4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydrothieno[3′,2′:4,5]cyclopenta[1,2-b]thieno[2″,3′′:3′,4′]cyclopenta[1′,2′:4,5]thieno[2,3-d]thiophene or 6,6,12,12-tetrakis(4-hexylphenyl)-6,12-dihydrothieno[2″,3′′:4′,5′]thieno[3′,2′:4,5]cyclopenta[1,2-b]thieno[2‴,3‴:4″,5′′]thieno[2″,3′′:3′,4′]cyclopenta[1′,2′:4,5]thieno[2,3-d]thiophene as central unit and weak electron-withdrawing benzo[c] [1,2,5] thiadiazole-4-carbonitrile as termini, which were connected by C–C single bond. Both molecules exhibited medium optical bandgap and high-lying frontier molecular orbital energy levels, which were matched with those of the representative low-cost polymer donor P3HT. Moreover, 4TBTCN and 6TBTCN showed high stability under continuous illumination and base condition, owing to a lack of exocyclic vinyl group between the central unit and end group. Compared to P3HT:6TBTCN, P3HT:4TBTCN blend system displayed lower miscibility and thus more distinct phase separation, leading to more efficient charge transport and collection. Although the LUMO energy level of 4TBTCN was 0.15 eV deeper than that of 6TBTCN, the energy loss for P3HT:4TBTCN based device was similar to that of P3HT:6TBTCN based device. As a result, P3HT:4TBTCN based device displayed a similar open-circuit voltage but higher fill factor and short-circuit current density, yielding a superior power conversion efficiency, in comparison to P3HT:6TBTCN based device. This work provides a new strategy for design of efficient and stable acceptor molecules.

Fluorinated carbon nanotubes as nonvolatile additive to the active layer of polymer/fullerene solar cells

Highly dispersed fluorinated SWCNTs of submicron length were prepared, characterized and tested as nonvolatile additive to the active layer of polymer/fullerene organic solar cells. Two types of initial SWCNT materials – TUBALL® (OCSiAl) and Super purified plasma tubes (Nanointegris Inc.) – were used. The absence of big CNT aggregates was revealed by atomic force microscopy. The absence of metallic SWCNTs is confirmed by optical spectra of fluorinated SWCNT dispersions. Reproducible increase of the main performance parameters of solar cells (short circuit current, open circuit voltage, fill factor and power conversion efficiency) was obtained upon admixing a small amount of fluorinated SWCNTs (less than 1% weight) into the polymer/fullerene active layer, with either P3HT or PCDTBT donor and either PC60BM or PC70BM acceptor for both direct and inverted device architectures. Since effective charge mobility did not change upon fluorinated SWCNT admixture, the improvement of solar cell performance is not related to SWCNT-induced modification of the electronic structure of the active layer components or charge transfer via fluorinated SWCNTs. Presumably, the origin of this improvements is geometric optimization of the active layer morphology (improving connectivity of donor and acceptor domains) by fluorinated SWCNTs due to their high aspect ratio.

Janus organic semiconductor nanoparticles prepared by simple nanoprecipitation

Nanoparticles (NPs) of donor–acceptor organic semiconductors are produced by a one-step nanoprecipitation with Janus morphology. Electron donor P3HT was blended with electron acceptor PC61BM in tetrahydrofuran and then precipitated in water, first with surfactant and second without surfactant. Cryogenic transmission electron microscopy reveals an internal Janus structure at high magnification, for NPs which have, in the past, been reported to have a molecularly intermixed morphology. Synchrotron-based scanning transmission X-ray microscopy confirmed the segregation of the organic semiconductors and photoluminescence experiments showed an efficient electron transfer from P3HT to PC61BM. Organic field effect transistors were fabricated with these Janus NPs and showed that the positive charges can be efficiently transported through thin films. This behavior proves that the NPs possess an electron-accepting face (the PC61BM face) able to transport electrons and a hole-accepting face (the P3HT face) for the conduction of holes. Finally, the deposition of silver via the photoreduction of a silver salt (AgNO3(aq)) was demonstrated, as a proof of concept. These experiments show the potential of the Janus NPs for photovoltaics but also photocatalytic reactions in which reduction and oxidation reactions can occur at opposite sides of the nanoreactor (the individual Janus NPs).

Designing easily synthesizable non-fused small acceptors for organic solar cells

A new strategy of implementing intramolecular noncovalent interactions (INCIs) has been adopted to design readily synthesizable acceptors for enhancing power conversion efficiency (PCE) and interfacial modifications of organic solar cells (OSCs). Computational approaches like density functional theory (DFT) have contributed to enterprise and analyze in what manner distinct chromophore components interact to produce optical transitions as well as orbital energy levels. This research focuses on a thorough and general overview of five designed conjugated molecular systems (BTZM1-BTZM5) possessing non-covalent conformational locking as well as evaluations using DFT. After incorporating INCIs (SO, SN, and S-F) into structured backbones, the resultant acceptor materials (BTZM1-BTZM5) showed tunable energy levels, reduced band gaps, enhanced absorption maximum, minimum binding energy, improved dipole moments and charge mobilities. Upon coupling BTZM5 acceptor with P3HT donor the blended film created a uniform surface and tighter π-π stacking ensuing VOC of 2.20 eV. Various computational analysis of molecules has been conducted to further confirm the nature of interactions such as TDM, DOS, FMOs, and RDG. Thus, the occurrence of many INCIs to closely lock the conformation of organic π-conjugated molecules is essential to improve the effectiveness of OSCs.

Influence of Cathode Materials on the Efficiency of PTB7:PC70BM Bulk Heterojunction Solar Cells

Herein, studies on the influence of the cathode metal work function (W) on electric parameters of PEDOT:PSS/PTB7:PC70BM/metal solar cells, especially their power conversion efficiency (PCE) and open‐circuit voltage (Voc), are reported. Along with standard cathode materials, like Al and Ag, 12 more metals and metal bilayers, In, InAl, Al3004 alloy, CaAl, MgAl, ZnAl, Sn, Ti, Au, TiAu, and Ni, are checked. It is found that although the photo‐voltage is generated mainly in the active layer, the W of cathode also affects Voc and the overall efficiency. Voc increases with W and the linear coefficient is about 0.33–0.39. A similar effect is observed for solar cells with P3HT donor material. The electrical and optical properties of the cells with different cathodes just after preparation are investigated and aging measurements are also conducted. The highest PCE is obtained for InAl cathode, 4.9%, which is better than for pure Al cathode. Moreover, long‐time measurements show that the cells with InAl cathode degrade about two times slower than the cells with Al electrode. Photocurrent spectroscopy reveals a blue shift of the solar cell sensitivity spectrum with an increase of W which is probably due to state filling (Burstein–Moss effect).

Quantum chemical approach to study TIPSTAP derivatives with anticipated minimized crystal roughness for photovoltaic application with estimated PCE of over 20%

In this study, we probed the TIPSTAP molecule, which is highly appropriate for developing organic photovoltaic cells, but its use was hampered due to crystal brittleness and limpidity. As an alternate to TIPSTAP, we disclosed four molecules derived from the TIPSTAP thanks to the alteration with the acceptor groups at the hub and ter. butyl group to substitute phenylic hydrogen atoms. All the molecular structures have been analyzed with a DFT approach, and obtained results are compared with TIPSTAP. The bandgap curtails up to 24% in engineered molecules, enhancing the charge transfer properties. These molecules showed improved photophysical properties at the longer wavelength relevant for photovoltaic cells. To enhance the open-circuit voltage, designed acceptors molecules are aligned with the P3HT donor, improving photovoltaic performance. The power conversion efficiency of TIPSTAP, TAPTA1, TAPTA2, TAPTA3, and TAPTA4 with short circuit current density of 9, 12, and 15 mAcm−2 ranges from 20 to 35% at a constant molecular open-circuit voltage that is better than pristine TIPSTAP or P3HT.

Low Cost Synthesis and Characterization of Donor P3HT Polymer for Fabrication of Organic Solar Cell

Over the years, the conjugated polymers acts as electron donor material in the active layer of Organic solar cells (OSCs). By altering means of doping, prepare a composite with suitable materials from Poly (p-phenylene vinylene) PPV polymer toPM6 polymer which gives Power conversion efficiency (PCE) can vary from ~ 2% to ~15%. But these are expensive, complicated synthetic procedure and less availability. To overcome this,the conjugated polymer Poly (3-Hexyl Thiophene)(P3HT) synthesized through oxidative coupling of 3-HT monomer and Ferric chloride (FeCl3) as an oxidant which is low cost, available and very easy method of synthesis. We investigated synthesized P3HT material that shows the Fourier Transform Infrared(FTIR) peaks shows that intramolecular interactions from thiophene ring, alkyl chain and polymer chain, FESEM Images reveals morphology consists of condensed layers in micrometer dimensions and Cyclic voltammetry studies gives oxidation and reduction potentials to promote the higher ionization potential of the compound to use as donor material in OSCs.

Investigation of Dye Dopant Influence on Electrooptical and Morphology Properties of Polymeric Acceptor Matrix Dedicated for Ternary Organic Solar Cells.

The publication presents the results of investigations of the influence of dye dopant on the electrooptical and morphology properties of a polymeric donor:acceptor mixture. Ternary thin films (polymer:dye:fullerene) were investigated for potential application as an active layer in organic solar cells. The aim of the research is to determine the effect of selected dye materials (dye D131, dye D149, dye D205, dye D358) on the three-component layer and their potential usefulness as an additional donor in ternary cells, based on P3HT donor and PC71BM acceptor. UV–vis spectroscopy studies were performed, and absorption and luminescence spectra were determined. Ellipsometry parameters for single dye and ternary layers have been measured. The analyses were performed using the Raman spectroscopy method, and the Raman spectra of the mixtures and single components have been determined. Organic layers were prepared and studied using scanning electron microscope and atomic force microscope. For dyes, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy studies were carried out and the ternary system was presented and analyzed in terms of energy bands.

Unfused Nonfullerene Acceptors Based on Simple Dipolar Merocyanines.

Merocyanine (MC) dyes exhibit facile synthesis and attractive optical properties, making them widely studied as the donor materials in organic solar cells (OSCs). In this study, for the first time, simple indole-based MCs are successfully designed as unfused nonfullerene acceptors (NFAs) for OSCs by forming dimers with A-D-π-D-A structure, which possess enhanced photostability compared to the well-known ITIC acceptor and high electron mobility in blend films. When blended with P3HT donor, one of the dimers, i. e. Z2, shows a good cell efficiency of 3.53 %, which outperforms the performance of most of P3HT/NFA blends, particularly for unfused systems, and thus indicates good potential of simple MCs as NFAs.

Calamitic-Type Dipolar and Quadrupolar Chromophores with a Twisted Peripheral Handle: Structure–Property Outlook as Nonfullerene Acceptors for Binary Solar Cells

Symmetrical (14, 15) and unsymmetrical (16, 17) molecules possessing tetracyanobutadiene (TCBD) as a twisted end group on the carbazole/fluorene backbone were synthesized as nonfullerene acceptors (NFAs). Systematic structural correlation of these chromophores on the optoelectronic, electrochemical, and physicochemical properties revealed better acceptor properties for symmetrical (14, 15) compared to unsymmetrical analogues (16, 17). High molar absorptivity, deep HOMO–LUMOs, better electron-accepting capacity, along with other complementary molecular properties are some of the associated factors for the better acceptor character. In a binary solar cell configuration blended with P3HT donor, quadrupolar-type symmetrical chromophores (14, 15) displayed higher power conversion efficiencies over dipolar-type unsymmetrical chromophores (16, 17). In particular, 14 with an efficiency of 5.37% emerged as the best candidate with further enhancement to 6.30% upon additive processing. The dependence of processing on the improved photoinduced current was attributed to the better nanoscale morphology, crystallinity, and electron mobility. In terms of efficiency, it is the third highest for any TCBD-based NFA solar cells. Overall, this work validates the impact of a nonplanar TCBD auxiliary positioned within a calamitic-type π-framework to realize alternative NFAs. Viewed from a fundamental perspective, the initial results are promising, and further fine tuning of the molecular structure could possibly form an ideal acceptor for organic photovoltaics.

Comparative Investigation of Fullerene PC71BM and Non-fullerene ITIC-Th Acceptors Blended With P3HT or PBDB-T Donor Polymers for PV Applications

Fundamentally, organic solar cells (OSCs) with a bulk-heterojunction active layer are made of at least two electronically dissimilar molecules, in which photoabsorption in one (donor) generates Frenkel excitons. The formation of free charge carriers emerge after exciton dissociation at the donor:acceptor interface. In the past decade, most of the progress in enhanced device performance has been steered by the rapid development of novel donor and acceptor materials and on device engineering. Among these donor materials, regioregular poly(3-hexylthiophene) (P3HT) produced better performance despite the mismatch of its absorption coefficient with the solar emission spectrum. Comparatively the donor PBDB-T exhibits an outstanding absorption coefficient with a deeper-lying highest occupied molecular orbital (HOMO) level. Previously most of the efficient acceptors were based on fullerene molecules characterized by limited photoabsorption and stability. In contrast, the recently developed non-fullerene OSCs have a tunable absorption spectrum and exhibit improved stability. In this work, we explore the fundamental sources of the differences in the device performance for different blend compositions made of fullerene derivative (PC71BM) and non-fullerene (ITIC-Th) when paired with the polymer donors P3HT and PBDB-T. The characteristic changes of the optical properties of these blends and their roles in device performance are also investigated. We also studied charge generation where PBDB-T:PC71BM showed the highest maximum exciton generation rate (Gmax) of 3.22 × 1028 s–1 while P3HT: ITIC-Th gave the lowest (0.96 × 1028 s–1). Also noted, PC71BM based counterparts gave better charge transfer capabilities as seen from the lower PL quenching and higher charge carrier dissociation plus collection probability P(E,T) derived from a plot of Jph/Jsat ratio under short-circuit conditions against the effective voltages.

Bis(pyrrolidino)[60]fullerenes: promising photostable fullerene-based acceptors suppressing light-induced absorber degradation pathways

Two novel highly soluble bis(pyrrolidino)[60]fullerenes were synthesized and investigated as promising electron acceptor materials for organic solar cells. Reduced electron affinity of bis(pyrrolidino)[60]fullerenes as compared to the reference [60]PCBM enabled a spectacular increase in open-circuit voltage of organic bulk heterojunction solar cells by ~200 mV while using model P3HT and PCDTBT electron donor polymers. In addition to the improved optoelectronic properties, bis(pyrrolidino)[60]fullerenes were found to be resistant towards the photochemical cross-linking in contrast to conventional [60]PCBM and conjugated polymers. Most importantly, the designed fullerene derivatives efficiently suppressed photooxidation of conjugated polymers as revealed by ESR spectroscopy, which features a tremendous potential of applying these materials in the development of efficient and durable organic photovoltaics.

On the physical and photo-electrical properties of organic photovoltaic cells based on 1,10-Phenanthroline and 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphine non-fullerene thin films

The active layer of the bulk heterojunction organic photovoltaic cells is typically based on a polymeric blend containing a donor polymer and a fullerene-based polymer electron acceptor. However, in the last decade non-fullerene polymer-based solar cells have seen a rapid progress, due to their extraordinary chemical, thermal and photo stability, and because of their ability to decrease the voltage loss. The conventional Organic Photovoltaic Cells (OPVs), structures based on either P3HT:PCBM bulk heterojunction (BHJ) polymeric blend or P3HT/PCBM bilayer heterojunction, have limited efficiency and stability, in principal due to the fullerene derivatives used as acceptor component. PCBM for example, as many other fullerene derivatives, exhibits some deficiencies, such as: limited chemical and energetic tunability, small range of absorption spectra, morphological instability and relatively high production costs. That is why in the last years, novel non-fullerene materials started to be used in order to overcome the above limits associated with the fullerene acceptors. In this paper two different non-fullerene acceptor materials have been tested as potential candidates for the efficient OPVs based on P3HT donor polymer as main absorber: a new conjugated polymer containing chelating ligands like 1,10-Phenanthroline (Phen), and a small-molecule acceptor like 5,10,15,20-Tetra(4-pyridyl)-21H,23H-porphine (TPyP). For both cell configurations a decrease of the voltage loss was obtained, and it was also observed that the thickness of the P3HT donor layer has an important contribution to the output power (Pmax) and fill factor (FF) of the OPV structures (FF and Pmax increased almost two times by decreasing the thickness of the P3HT donor layer).

Blending with a phthalocyanine leads to improved P3HT donor layers for OPVs

Ternary blended solar cells have been intensively studied in recent years, where the addition of a second donor material in the active layer tends to increase the current density through improved photon absorption along with improving the charge transport properties and the inhibition of charge recombination processes. Here, we investigated a donor layer composed of a liquid crystalline cobalt phthalocyanine (CoPc) and poly(3-hexylthiophene-2,5-diyl) – P3HT. The CoPc presents a complementary absorption spectrum in the near infrared region and compact anisotropic molecular arrangement to promote efficient charge migration. The energy levels of CoPc are properly located between the corresponding levels of P3HT and PCBM, forming an energy cascade alignment. The P3HT/CoPc blend showed improved photophysical and electrical response depending on the CoPc concentration and thermal annealing. We demonstrated that molecular order, morphology and energetic barrier at cluster interfaces are competing effects and need to be taken into account to optimize charge transport.

Star-shaped A-D-A compounds synthesized by different methods and used as donor or acceptor materials in organic photovoltaics

Star-shaped small molecule has lots of fascinating advantages compare with the linear small molecule. In this paper, two star-shaped small-molecules (S-TT and S-TT-R) with vinyl trithiophene with or without alkyl substituents as core, N-ethylrhodanine as terminal and withdrawing groups, vinyl as bridge group were synthesized by different synthetic routes. Both of the two materials demonstrate high thermal stability and broad absorption. Both S-TT and S-TT-R exhibit narrow bandgap (1.72 and 1.82 eV), low LUMO energy levels (− 3.92 eV) for S-TT and high HOMO energy levels (− 5.37 eV) for S-TT-R which could be applied as acceptor or donor materials for photovoltaics, respectively. Both of the two compounds were used as donor materials with PC61BM acceptor and S-TT were used as acceptor material with P3HT donor.

Effects of interfacial ligand type on hybrid P3HT:CdSe quantum dot solar cell device parameters

A series of CdSe quantum dot acceptors possessing six different ligand frameworks (i.e., pivalic acid, pyridine, butylamine, tert-butylthiol, thiophenol, and tetrahydrothiophene) were used as platforms for investigating the influence of quantum dot surface chemistry on the performance of hybrid poly(3-hexythiophene-2,5-diyl) (P3HT):CdSe quantum dot bulk heterojunction (BHJ) solar cells. We confirm that the device parameters used to evaluate solar cell performance are significantly influenced by the nature of the quantum dot surface ligand. The dependence of short circuit current density (JSC) on the CdSe ligand type was probed using ultrafast time-resolved photoluminescence (PL) measurements, and good correlations between the ligand-dependent trends in JSC and excited state lifetime were found, in which the P3HT:CdSe quantum dot BHJs with the shortest PL lifetimes possess the largest device current densities. The frontier energy levels of the quantum dot acceptors are significantly influenced by surface ligands, wherein the device open circuit potentials (VOC) were found to linearly correlate with the energy difference (ΔEDA) between the HOMO of the P3HT donor and the electrochemically determined LUMO of the CdSe quantum dot acceptors over a range of 220 mV. This work demonstrates the versatility of quantum dot ligand engineering for tuning the device parameters and performance of hybrid solar cells.

Rhodanine-based nonfullerene acceptors for organic solar cells

Significant progress on the development of non-fullerene acceptors (NFAs) for organic solar cells (OSCs) has been made in the past several years, and the power conversion efficiency (PCE) exceeding 17% has been already realized based on a tandem non-fullerene device. To date, NFAs with a linearly fused acceptor-donor-acceptor (A-D-A) structure are of great interest, due to their attracting synthetic flexibility and high photovoltaic performance. Rhodanine is one of the most studied electron-withdrawing moieties to construct such A-D-A type NFAs, and the resulting single-junction OSCs have produced PCEs of ~10%. More interestingly, those rhodanine-based NFAs have demonstrated a particularly excellent compatibility with well-known P3HT donor, enabling respectable PCEs over 7%. Thus in this review, we summarize the important advances on rhodanine-based NFAs with a main focus on discussing the molecular design strategies, providing a better understanding of the structure-property relationship for those rhodanine-based NFAs.

Excitation Wavelength-Dependent Internal Quantum Efficiencies in a P3HT/Nonfullerene Acceptor Solar Cell

The authors declare no competing financial interests. The author CH Tan thanks Malaysian Government MyBrainSc for the funding and also Matthew Davies from Swansea University for providing PL excitation spectroscopy instrument. Funding from the KAUST project OSR-2015-CRG-2572 is gratefully acknowledged. The authors also thank KAUST for financial support and acknowledge EC FP7 Project SC2 (610115), EC H2020 (643791), and EPSRC Projects EP/G037515/1 and EP/M005143/1.

Tuning charge transfer at the electron donor/acceptor assembly through vibration-induced aggregation of P3HT chains in solution

Abstract In this report, we developed a test platform to probe charge transfer at a model electron donor/acceptor system in which charge transfer rate is investigated through electrical contact resistance in a metal oxide/organic semiconductor/metal oxide structure using transmission line method (TLM). Aluminum (Al)-doped zinc oxide (AZO) films were adopted as source and drain electrodes. Molecular ordering of the organic semiconductor was systematically varied through vibration-induced aggregation (VIA) treatment of poly(3-hexylthiophene) (P3HT) polymer chains in solution to probe the effect of molecular ordering of P3HT (donor) in contact with AZO (acceptor) on interfacial charge transfer at the electron donor (P3HT)/acceptor (AZO) interface crucial in determining device performance of optoelectronic devices. Enhanced charge transfer at the donor/acceptor interface containing P3HT film treated with VIA process was demonstrated by reduction of the contact resistance via TLM. More efficient charge transfer at the AZO/sonicated-P3HT/AZO compared with AZO/pristine-P3HT/AZO results from enhanced charge carrier mobility of P3HT near the interface, blocking back-transfer of injected holes from P3HT to the AZO electrode, as demonstrated by theoretical prediction. Effect of VIA treatment on charge transfer at the electron donor/acceptor interface is confirmed through comparing the AZO/P3HT contact resistance depending on the degree of VIA for P3HT polymer chains by varying sonication time. Our work presented here demonstrates that improvement in structural arrangement of polymer chains leads to efficient charge transfer at interface.

Sulfanilic Acid Pending on a Graphene Scaffold: Novel, Efficient Synthesis and Much Enhanced Polymer Solar Cell Efficiency and Stability Using It as a Hole Extraction Layer.

In this contribution, we describe a novel, facile, and scalable methodology for high degree functionalization toward graphene by the reaction between bulk graphite fluoride and in situ generated amine anion. Using this, the rationally designed sulfanilic acid pending on a graphene scaffold (G-SO3H), a two-dimensional (2D) π-conjugated counterpart of poly(styrenesulfonate), is available. Combined reliable characterizations demonstrate that a very large quantity of sulfanilic blocks are linked to graphene through the foreseen substitution of carbon-fluorine units and an unexpected reductive defluorination simultaneously proceeds during the one-step reaction, endowing the resultant G-SO3H with splendid dispersity in various solvents and film-forming property via the former, and with recovered 2D π-conjugation via the latter. Besides, the work function of G-SO3H lies at -4.8 eV, well matched with the P3HT donor. Awarded with these fantastic merits, G-SO3H behaves capable in hole collection and transport, indicated by the enhanced device efficiency and stability of polymer solar cells (PSCs) based on intensively studied P3HT:PCBM blends as an active layer. In particular, comparison with conventional poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) and recently rising and shining graphene oxide, G-SO3H outperforms above 17 and 24%, respectively, in efficiency. More impressively, when these three unencapsulated devices are placed in a N2-filled glovebox at around 25 °C for 7 weeks, or subject to thermal treatment at 150 °C for 6 h also in N2 atmosphere, or even rudely exposed to indoor air, G-SO3H-based PSCs exhibit the best stability. These findings enable G-SO3H to be a strongly competitive alternative of the existing hole extraction materials for PSC real-life applications.