Thieno[3,4-c]pyrrole-4,6-dione Research Articles

Development of Two Novel Dibenzosilole-Based Conjugated Polymers with Thieno[3,4-c]pyrrole-4,6-dione for Use in Polymer Solar Cells

The donor-acceptor (D-A) strategy has proven to be one of the most effective methods for tuning the band gaps, absorption characteristics, and optoelectronic properties in conjugated polymers. Two novel D-A conjugated polymers, PDBSTPD-1T and PDBSTPD-2T, were synthesized using dibenzosilole (DBS) and thieno[3,4-c]pyrrole-4,6-dione (TPD) as the building blocks. These polymers were linked through either a single thiophene or two thiophene rings as π-bridges and were copolymerized using a Suzuki coupling reaction. The effect of the incorporation of the different π-bridges on the electrical/optical properties of the prepared copolymers was also investigated. The synthesized polymers, PDBSTPD-1T and PDBSTPD-2T, were soluble in organic solvents and demonstrated high molar mass along with excellent thermal stability. The conjugation of the electron-accepting TPD unit with the electron-donating DBS unit produced relatively deep HOMO levels, which were fine-tuned to be −5.44 and −5.36 eV via the addition of the different π-bridges. PDBSTPD-1T and PDBSTPD-2T displayed absorption wavelengths between 350 and 650 nm with high Eg opt of 2.01 and 1.97 eV, respectively. X-ray diffraction analysis presented several diffraction peaks, and the π-π stacking distances of PDBSTPD-1T and PDBSTPD-2T were 3.45 and 3.65°A, respectively.

Isomers of n-Type Poly(thiophene-alt-co-thiazole) for Organic Thermoelectrics.

n-Type polythiophene represents a promising category of n-type polymer thermoelectric materials known for their straightforward structure and scalable synthesis. However, n-type polythiophene often suffers from a twisted backbone and poor stacking property when introducing high-density electron-withdrawing groups for a lower lowest unoccupied molecular orbital (LUMO) level, which is considered to be beneficial for n-doping efficiency. Herein, we developed two isomers of polythiophene derivatives, PTTz1 and PTTz2, by inserting thiazole units into the polythiophene backbone composed of thieno[3,4-c]pyrrole-4,6-dione (TPD) and thiophene-3,4-dicarbonitrile (2CNT). Although PTTz1 and PTTz2 share a similar polymer skeleton, they differ in thiazole configuration, with the nitrogen atoms of the thiazole units oriented toward TPD and 2CNT, respectively. The insertion of thiazole units significantly planarizes the polythiophene backbone while largely preserving low LUMO levels. Notably, PTTz2 exhibits a more coplanar backbone and closer π-stacking compared to PTTz1, resulting in a greatly enhanced electron mobility. Both PTTz1 and PTTz2 can be easily n-doped due to their deep LUMO levels. PTTz2 demonstrates superior thermoelectric performance, with an electrical conductivity of 50.3 S cm-1 and a power factor of 23.8 μW m-1 K-2, which is approximately double that of PTTz1. This study highlights the impact of the thiazole unit on n-type polythiophene derivatives and provides valuable guidelines for the design of high-performance n-type polymer thermoelectric materials.

Impact of the alkyl side-chain length on solubility, interchain packing, and charge-transport properties of amorphous π-conjugated polymers

Increasing the length of alkyl side chains is a typical way to improve the solubility of π-conjugated polymers designed for use in solution-processed devices. However, these modifications have also been reported to alter the film morphology. Given that the mechanism leading to improved solubility is not well documented yet and the nanoscale (local) morphologies of amorphous π-conjugated polymer films are difficult to characterize experimentally, here, we combine molecular dynamics simulations and long-range corrected density functional theory calculations to examine at the molecular scale the impact that the alkyl side-chain length has on polymer solubility and film morphologies. As a representative example, we consider poly(thieno[3,4-c]pyrrole-4,6-dione-alt-3,4-difluorothiophene) (PTPD[2F]T) with two different lengths of the alkyl side chains on the thieno[3,4-c]pyrrole-4,6-dione (TPD) moieties, i.e., 2-hexyldecyl (2HD) and 2-decyltetradecyl (2DT). A detailed analysis of polymer–solvent and polymer–polymer interactions provides a picture that describes the underlying mechanism for improved solubility in going from 2HD to 2DT. We then underline an intrinsic characteristic that decreasing the side-chain length brings a greater extent of backbone planarity and lesser side chain-TPD interactions, which leads to higher interchain π-π packing density and order, while the interchain π-π packing patterns remain similar in the two films. These morphologies are discussed in terms of the charge-transport properties between neighboring PTPD[2F]T chains, which point to a higher electron mobility in the PTPD[2F]T films with shorter alkyl side chains. Overall, our findings offer guidance in the field of solution-processed electronic devices by pointing out that the polymer alkyl side-chain length could be minimized to improve carrier mobility while ensuring polymer solubility.

Donor-acceptor-donor type AIEgens based on thieno[3.4-c]pyrrole-4,6-dione: Synthesis, electropolymerization, and electrochromism.

Photoelectric functional materials with electrochemical reversible activity and fluorescence intensities have attracted significant interest due to their wide range of applications in optoelectronic devices. In this work, a series of photoresponsive and electroactive monomers based on thieno[3.4-c]pyrrole-4,6-dione (TPD) are synthesized and characterized. They possess planar geometry with smaller dihedral angles owing to the existence of a noncovalent conformation lock coming from the S atoms and the O atoms. Crystallographic, spectroscopic, and computational results reveal that the introduction of the TPD unit can endow the monomers with aggregation-induced emission (AIE), reduced energy levels, and increased electrochemical activity. The monomers were successfully polymerized through the electrochemical method, and the corresponding polymers displayed reversible electrochemical activity and stability. Moreover, polymer films based on 3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (ProE)-TPD have electrochromic properties in the near-infrared field with a high value of optical contrast ratio (∆T) of 27.1% at 1000 nm.

Design, Synthesis, and Theoretical Studies on the Benzoxadiazole and Thienopyrrole Containing Conjugated Random Copolymers for Organic Solar Cell Applications.

In this study, six different donor-π-acceptor1-π-donor-acceptor2 type random co-polymers containing benzodithiophene as a donor, benzooxadiazole (BO), and thieno[3,4-c]pyrrole-4,6-dione (TPD) as acceptor, have been synthesized and characterized. In addition to the acceptor core ratio at different values, the effect of aromatic bridge structures on the optical, electronic, and photovoltaic properties of six different random co-polymers is investigated by using thiophene and selenophene structures as aromatic bridge units. To investigate how the acceptor unit ratio and replacement of aromatic bridge units impact the structural, electronic, and optical properties of the polymers, density functional theory (DFT) calculations are carried out for the tetramer models. The open-circuit voltage (VOC), which is strongly correlated with the HOMO levels of the donor material, is enhanced with the increasing ratio of the TPD moiety. On the other hand, the short-circuit current (JSC), which is associated with the absorption ability of the donor material, is improved by the increasing ratio of BO moiety with the π-bridges. BO moiety dominant selenophene π-bridged co-polymer (P4) showed the best performance with a power conversion efficiency (PCE) of 6.26%, a JSC of 11.44mAcm2, a VOC of 0.80V, and a fill factor (FF) of 68.81%.

Direct C–H arylation vs Stille polymerization: Rational design, synthesis, and systematic examinations of π-conjugated polymers for organic solar cells

Direct C–H arylation (DA) polymerization, often known as DArP, is an emerging protocol to the synthesis of π-functional polymers that has garnered a lot of attention due to its virtues of requiring a minimum number of synthetic steps and producing a simpler byproduct. However, the regioselectivity of the C–H bonds is significantly less effective in the DArP-derived polymers, which is one of the reasons why only a small number of these polymers exhibit photovoltaic characteristics that are equal to counterparts generated via Stille coupling. In this work, a low-defect π-polymer PBDTF-TPD (DA) is facilely obtained via DArP between 4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']-dithiophene (BDTF) and thieno [3,4-c]pyrrole-4,6-dione (TPD) that possesses regioselective π-C−H bonds toward arylation. As a result, DArP-derived PBDTF-TPD (DA) and Stille-derived PBDTF-TPD (St) share the similar opto-electrochemical properties, photovoltaic performance, and morphology, indicating that DArP polymerization leads to defined structures with minimal branching defects. Specifically, this study demonstrates that the (PCE = 8.91%) of a rationally designed monomer for DArP using an ideal approach is equivalent to that of the Stille-derived analogue PBDTF-TPD (St, PCE = 9.57%).

Incorporating Naphthalene and Halogen into Near-Infrared Double-Cable Conjugated Polymers for Single-Component Organic Solar Cells with Low-Voltage Losses.

The invention of near-infrared pedant-based double-cable conjugated polymers has demonstrated remarkable efficacy in single-component organic solar cells (SCOSCs). This work focuses on the innovative double-cable conjugated polymers aimed at attaining good absorption and suitable energy levels. Specifically, in the aromatic side units, the electron-donating (D) part is designed using a thieno[3,4-c]pyrrole-4,6-dione (TPD) as a core unit, flanked by two cyclopentadithiophene groups on either side. The electron-deficient (A) terminal groups consist of 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene) malononitrile (NC), which can be further modified through fluorination to modulate the physical properties and packing modes of the acceptor material. The resulting double-cable conjugated polymers exhibit broad absorption spectra spanning 500-850 nm and possess lowered Frontier energy levels when incorporating fluorine elements, providing decreased voltage losses in SCOSCs. Therefore, SCOSCs fabricated using these polymers have demonstrated power conversion efficiencies ranging from 7.6 to 10.2%, in which fluorine-containing double-cable conjugated polymers showed higher PCEs due to more favorable crystalline packing, enhanced exciton dissociation probability, and charge-transporting ability.

The effect of branched versus linear side chain on thieno[3,4-c]pyrrole-4,6-dione-based donor-acceptor-donor type monomers and their p- and n-dopable polymers

The conjugated backbone has been the focus of the most research, while the structure of the side chains has received less attention. Here, we focus on making new donor–acceptor–donor (D–A–D) type conjugated monomers by bearing a thieno[3,4-c]pyrrole-4,6-dione (TPD) with octyl chain at the imide nitrogen as the acceptor unit and 3,4-ethylenedioxythiophene (EDOT), and 3,3-didecyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT) as the donor units and their corresponding polymers. The optical and electrochemical properties of octyl substituted monomers and their corresponding polymers were compared with their ethylhexyl counterparts. Changing the alkyl side chain on the TPD unit from linear to branched has no effect on onset potential, optical band gap (Eg), perceived color, electrochromic contrast, or switching time. Nonetheless, donor strength has significant impact on the properties of monomers and their corresponding polymers. EDOT-bearing monomers and polymers have lower onset and oxidation potentials, Eg values than their ProDOT counterparts due to more electron donating ability of ethylenedioxy bridge in comparison to the propylenedioxy bridge. Octyl substituted monomers, P-Octyl and E-Octyl, demonstrated high sensitivity towards the Fe3+ ion, making them viable candidates for use in ion sensing, and their corresponding polymers, PE-Octyl and PP-Octyl, are both p- and n-dopable, which is a desirable property for conjugated polymers. Furthermore, PP-Octyl was found to be soluble in common solvents, and PP-Octyl in toluene can be oxidized with antimony pentachloride (SbCl5).

Effect of phthalimide and thieno[3,4-c]pyrrole-4,6,dione acceptors on π-conjugated donor-acceptor-donor monomers: Experimental and theoretical investigations of photophysical and electrochemical properties

In this study, two novel donor-acceptor-donor monomers were synthesized by coupling a phthalimide (PI) acceptor unit with thiophene (T) and ethylenedioxythiophene (EDOT (E)) donor units. These two novel PI-based monomers, namely 2-(2-ethylhexyl)-4,7-di(thiophen-2-yl)isoindoline-1,3-dione (T-PI) and 4,7-bis(2,3-dihydrothieno[3,4-b] [1,4]dioxin-5-yl)-2-(2-ethylhexyl)isoindoline-1,3-dione (E-PI), were fully characterized via UV–vis and fluorescence spectroscopy as well as electrochemical methods, and the results were directly compared with those of previously synthesized thieno[3,4-c]pyrrole-4,6-dione (TPD)-based analogues to report the results for four classes of monomers. In this regard, the effects of different donor groups and structural modifications in the acceptor unit as changed from PI to TPD have been investigated to reveal the precise effect of the donor and acceptor on the optical and electrochemical properties of the monomers. All monomers exhibits an intramolecular charge transfer band in the low energy region due to strong donor and acceptor interactions. The oxidation and reduction potentials of the monomers are found to vary depending on the strengths of both donor and acceptor units. PI-based monomers show more positive oxidation and less negative reduction potentials than TPD-based analogues. Similarly, thiophene-based analogues reveal the same trend in their oxidation and reduction potentials as compared to EDOT-based analogues. Lastly, PI-based monomers could not undergo polymerization via electrochemical method, unlike TPD-based monomers, since the dihedral angle arising between donor and PI acceptor disturbs molecular planarity significantly, as demonstrated by first principle calculations.

Non-fused polymerized small-molecular acceptors containing thieno[3,4-c]pyrrole-4,6-dione core for all-polymer solar cells

The innovation of polymer acceptors through the polymerized small molecular acceptors (PSMAs) strategy has promoted the rapid development of all-polymer solar cells (all-PSCs) in recent years. However, the non-fused PSMAs have been rarely investigated compared with the fused-ring non-fullerene counterpart. In this work, we reported the synthesis of non-fused PSMAs with thieno[3,4-c]pyrrole-4,6-dione (TPD) core, exhibiting planar configuration, simplified synthesis, and near-infrared absorption. Two PSMAs with regiorandom or regioregular structures were prepared based on the TPD core, in which all-PSCs offered efficiencies of 4.00% for the regiorandom polymer and 10.99% for the regioregular polymer, respectively, which is among the highest performance for non-fused PSMAs. Further morphological and electrical characterizations unveiled that higher device performance of regioregular TPD-based PSMAs was due to the efficient exciton separation and charge transport with more ordered backbone packing in the solid state. This work demonstrates that the TPD unit is a promising building block for the construction of PSMA polymers, providing more selections for the design of high-performance all-PSCs.

Synthesis of thieno[3,4-c] pyrrole-4,6-dione-based small molecules for application in organic thin-film transistors

The synthesis of two alternating donor-acceptor (D-A) small molecules revolving around thieno[3,4-c]pyrrole-4,6-dione (TPD) as the main acceptor building block is reported herein. The materials are synthesized using a robust Stille coupling to attach the TPD core with thiophene donors on either of its side, and completed with an aldol condensation under mild conditions for the addition of terminal secondary acceptor building blocks, representing a sought out A2-D-A1-D-A2 structure. The two newly synthesized materials are set to be used as organic semiconductors in organic thin-film transistor (OTFT) devices. Comparative optical, computational, and electrochemical studies were carried out on these new materials to investigate their ability to act as potential n-type organic semiconductors. The materials were then incorporated into bottom-gate bottom-contact OTFT devices, and subsequent thin-film engineering studies were done to probe the effects that solvent and post-deposition annealing conditions had on device performance. From these conditions, the rhodanine-derived D-A material exhibited the greatest electron field-effect mobility (0.011 cm2 V−1 s−1), and a threshold voltage of 20.1 V under vacuum.

Wide‐Bandgap Donor–Acceptor Copolymer Based on BDTTz Donor and TPD Acceptor for Polymer Solar Cells Using Fullerene and Nonfullerene Acceptors

A donor–acceptor copolymer based on thiazole substituted benzodithiophene (BDTTz) (donor unit) and thieno[3,4‐c]pyrrole‐4‐6‐dione (TPD) (acceptor unit) P(BDTTz‐TPD) denoted as P132 is investigated. P132 shows an absorption profile from 300 to 680 nm and the low‐lying highest occupied molecular orbital (HOMO) energy level of −5.54 eV. P132 as donor along with fullerene derivative (PC71BM) or nonfullerene denoted as BThIND‐Cl as acceptor are used for the fabrication of polymer solar cells. The P132:BThIND‐Cl‐based polymer solar cell shows high open‐circuit voltage as compared with P132:PC71BM which is attributed to the upshifted lowest unoccupied molecular orbital level of BThIND‐Cl and low energy loss. Moreover, P132:BThIND‐Cl attains higher short‐circuit current than that for P132:PC71BM which is attributed to the broader absorption spectra and low optical band gap of BThIND‐Cl, which leads to high light‐harvesting ability of the P132:BThIND‐Cl active layer. The polymer solar cells based on P132:PC71BM and P132:BThIND‐Cl attain power conversion efficiencies of 7.03% and 15.52%, respectively. The charge transport is more balanced in P132:BThIND‐Cl and results in a high value of fill factor. Small energy loss in P132:BThIND‐Cl‐based PSCs is attributed to the low HOMO offsets between P132 and BThIND‐Cl.

Acceptor-donor-acceptor π-extended systems based on α-dithiophenetetrathiafulvalene (α-DT-TTF): Facile synthesis and photoconductivity studies

π-Extended derivatives of the electron donor (D) α-dithiophenetetrathiafulvalene (α-DT-TTF) were prepared for the first time. The compounds consisting of α-DT-TTF covalently linked to N-alkylated phthalimides (Phth) or thieno[3,4-c]pyrrole-4,6-dione (TPD), as the acceptors (A), in a A-D-A arrangements, were synthesized through microwave-assisted Stille cross-coupling reactions. DFT calculations reveal that the α-DT-TTF unit is coplanar with the TPD plane while a light twist occurs with the Phth end-unit, causing highly planar conjugated cores which are favorable for stacking and intermolecular charge transport. The A-D-A molecular design leads to red-shifted absorption spectra, in comparison with α-DT-TTF, and accessible reduction potentials, as indicated by electrochemical studies. Finally, photoconductivity in the UV–visible, up to 550 nm, was measured in crystals of one of the new compounds with the acceptor phthalimide. This work opens the way for the synthesis of new α-DT-TTF derivatives which can have applications in the optoelectronics field.

Effect of random copolymerization on the optical properties of selenophene and thieno[3,4-c]pyrrole-4,6-dione conjugated polymers

For the preparation of conjugated polymers having targeted band gaps, absorption, and optoelectronic properties, the Donor-Acceptor (D-A) approach has been one of the most convenient methods. We synthesized four new conjugated polymers, bearing selenophene and thieno[3,4-c]pyrrole-4,6-dione (TPD) for this study via Suzuki Stille Polycondensation. The effect of selenophene that was inserted as π-bridge and the introduction of a second TPD unit into the polymer backbones through random polymerization were investigated. Optoelectronic properties of the polymers were analyzed via electrochemical and spectroelectrochemical studies. The study reveals the effects of TPD and selenophene moieties on absorption and band gaps of the polymer and provides a concise approach for the preparation of D-A conjugated polymers.

Thieno[3,4‐c]pyrrole‐4,6‐dione‐Based Conjugated Polymers for Nonfullerene Organic Solar Cells

AbstractDonor–acceptor (D–A) conjugated polymers have gotten significant attention in the past decades. Wide application area, ease of production, and cost‐effectiveness have made the D–A conjugated polymers a pivotal class of organic electronics. Organic solar cells (OSCs) became one of the most critical application areas of conjugated polymers among many. Up to the last decade, intensive research has been conducted on fullerene‐based OSCs. Drawbacks of fullerene derivatives like high cost, production obstacles, and difficulties in modifying molecular structure made the academia seek new alternatives. Emerging nonfullerene acceptors (NFAs) draw a new path for academia to tune OSCs' power conversion efficiency (PCE). With the ease of synthesis and purification, modification of molecular structure via various functional groups, NFAs start outperforming fullerene‐based acceptors. Thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) is widely used in D–A conjugated polymers for high‐performance OSCs. As a strong electron‐withdrawing group, TPD provides deepened lowest unoccupied molecular orbital energy level and wide bandgaps when introduced into polymer backbones, enhancing optoelectronic properties photovoltaic performance. Herein, an overview of the applications of TPD‐based donor and acceptor type conjugated polymers for nonfullerene and all‐polymer solar cells in the last 5 years is provided.

Polyhedral oligomeric silsesquioxanes appended conjugated soluble polymers based on thieno[3,4-c]pyrrole-4,6‑dione acceptor unit

A series of new donor-acceptor-donor type fluorescent molecules incorporating thieno[3,4-c]pyrrole-4,6‑dione (TPD) as the acceptor unit were synthesized. TPD acceptor unit was modified with polyhedral oligomeric silsesquioxanes (POSS) cages and integrated with thiophene and alkylenedioxythiophene derivatives (3,4-ethylenedioxythiophene (EDOT) and 3,4-propylenedioxythiophene (ProDOT)) using Stille coupling reaction. The monomers, T2-POSS, E2-POSS, and P2-POSS, were polymerized successfully via electrochemical and chemical polymerization techniques. As a fingerprint of d-A-D monomers, all monomers showed dual band characteristics due to intramolecular charge transfer. Soluble polymers exhibited reversible electrochromic responses electrochemically and chemically with fast switching times and high coloration efficiencies. E2-POSS and its polymer PE2-POSS exhibited the lowest oxidation potential and band gap values as compared to their thiophene and ProDOT analogs. Also, P2-POSS and its chemically obtained fluorescent polymer PP2-POSS-C represented high sensitivity towards Fe2+ and Fe3+ ions, which makes them potential candidates to be amenable for use in ion sensing.

The alkyl chain positioning of thieno[3,4-c]pyrrole-4,6-dione (TPD)-Based polymer donors mediates the energy loss, charge transport and recombination in polymer solar cells

Tailoring the alkyl chains of polymeric photovoltaic materials is a cost-effective strategy towards efficient polymer solar cells (PSCs). However, the alkyl chain positioning effect of polymers on the photovoltaic performance remains a crucial issue to be examined. In this contribution, three thieno [3,4-c]pyrrole-4,6-dione (TPD)-based donor polymers 2HD/C8, C8/2BO/C6, and 2BO/C6/C6, in which alkyl side chains are appended at different positions, are developed and examined. Studies show that polymer 2HD/C8 largely outperforms its other two analogues C8/2BO/C6 and 2BO/C6/C6. Results make clear that (i) dispersing alkyl side-chain from the N-site of thieno [3,4-c]pyrrole-4,6-dione (TPD) motifs to the 4,8-di(thiophen-2-yl)benzo [1,2-b:4,5-b']dithiophene (BDTT) or to the backbone thiophene units leads to less crystallinity and decreased face-on packing ratio in correlated BHJ films; (ii) the hole (μh) and electron mobility (μe) show gradual reduction from 2HD/C8- to 2BO/C6/C6-, and further to 2BO/C8/C6-based BHJ devices, which result in serious charge recombination, decreased FF and JSC in the corresponding BHJ devices; (iii) the alkyl chain positioning also impacts the energy levels due to the hyperconjugation effect of alkyl chains, consequently, distinct VOC and energy loss are observed. This examination sheds light on that meticulous tailoring the alkyl chain positions should be considered when developing high-performing polymeric photovoltaic materials.

A comprehensive study: Theoretical and experimental investigation of heteroatom and substituent effects on frontier orbitals and polymer solar cell performances

AbstractBenzochalcogendiazole derivatives are incorporated with thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) acceptor and 4,8‐diethoxybenzo[1,2‐b:4,5‐b′]dithiophene donor to synthesize tree‐component random copolymers. Four different copolymers are synthesized and their electronic, optical and photovoltaic properties are compared. Comparisons are aligned in the course of two different strategies, which are the replacement of benzochalcogendiazole moiety and the modification of side group on benzothiadiazole. Theoretical calculations by comparing the HOMO‐LUMO levels, band gaps and other electronic descriptors of pristine and 2 + 2 two acceptor‐based copolymers are investigated. Random copolymer bearing benzoxadiazole moiety, PO exhibits the highest photovoltaic performance of 8.29% with a Jsc of 14.96 mA cm−2, Voc of 0.87 V, fill factor (FF) of 63.70%. PF possesses the highest Voc with a value of 0.88 V, Jsc of 14.40 mA cm−2, power conversion efficiency (PCE) of 7.32% with 58% FF. PS exhibits average feature with Jsc 11.82 mA cm−2, Voc 0.80 V, FF 50%, and 4.72% PCE. Lowest performing selenadiazole containing random copolymer (PSe) copolymer exhibits maximum PCE as 3.65%. These results demonstrate the promising effectiveness of benzoxadiazole selection as an alternative acceptor unit and F atom substitution for the design of (A1‐D)‐(A2‐D) type random copolymers for organic solar cells.

Synthesis of random copolymer using Zig-Zag Naphthodithiophene for bulk Heterojunction polymer solar cell applications

Synthesized a random copolymer here, namely P(zNDT-TPDBT), consisting of an electron-rich unit ‘zig-zag’ 4,9-bis-(2-ethylhexyloxy)naphtho[1,2-b:5,6-b’]dithiophene (zNDT) and different ratio of two-electron acceptor units of thieno[3,4-c]pyrrole-4,6-dione (TPD) and benzodiathiazole (BT) via Stille coupling polymerization. The photophysical, electrochemical, and photovoltaic properties of P(zNDT-TPDBT) were investigated. The differences in the photophysical property of P(zNDT-TPDBT) indicate (i) red-shifted and broadening absorption spectrum located at 509 nm in thin-film as compared to solution (λmax = 492 nm) (ii) the fluorescence spectrum shows dual emission bands at 545 nm and 608 nm in the longer wavelength in solution, however, relatively complete quenching fluorescence property was observed in blended film with PC71BM. The copolymer exhibited an optical bandgap of 2.03 eV, with a highest occupied molecular orbital (HOMO) level of −5.87 eV. The optimized structure for the copolymer was also determined through DFT calculation. The bulk-heterojunction (BHJ) polymer solar cell (PSC) with a device structure of ITO/PEDOT:PSS/P(zNDT-TPDBT):PC71BM/Al exhibited a promising efficiency of 2.4% with the short circuit current density (Jsc) of 5.7 mA cm−2, open-circuit voltage (Voc) of 0.91 V, and fill factor (FF) of 47%, without processing addictive. The clear correlations between film morphology and device efficiency were observed through atomic force microscopy technique.

Shorter alkyl chain in thieno[3,4-c]pyrrole-4,6-dione (TPD)-based large bandgap polymer donors – Yield efficient non-fullerene polymer solar cells

Typically, conjugated polymers are composed of conjugated backbones and alkyl side chains. In this contribution, a cost-effective strategy of tailoring the length of alkyl side chain is utilized to design high-performing thieno[3,4-c]pyrrole-4,6-dione (TPD)-based large bandgap polymer donors PBDT-BiTPD(Cχ) (χ = 48, 52, 56), in which χ represents the alkyl side chain length in term of the total carbon number. A combination of light absorption, device, and morphology examinations make clear that the shorter alkyl side chains yield (i) higher crystallinity and more predominant face-on crystallite orientation in their neat and BHJ blend films, (ii) higher charge mobilities (6.7 × 10−4 cm2 V−1 s−1 for C48 vs. 3.2 × 10−4 cm2 V−1 s−1 for C56), and negligible charge recombination, consequently, (iii) significantly improved fill-factor (FF) and short current (JSC), while almost the same open circuit voltage (VOC) of ca. 0.82 V in their corresponding BHJ devices. In parallel, as alkyl side chain lengths decrease from C56 to C48, power conversion efficiencies (PCEs) increased from 7.8% for C56 to 11.1% for C52, and further to 14.1% for C48 in their BHJ solar cells made with a narrow bandgap non-fullerene acceptor Y6. This systematic study declares that shortening the side chain, if providing appropriate solubility in device solution processing solvents, is of essential significance for developing high-performing polymer donors and further improving device photovoltaic performance.