Donors For Cells Research Articles

Accelerated discovery of polymer donors for organic solar cells through machine learning: From library creation to performance forecasting

The design of novel polymer donors for organic solar cells has been a major research focus for decades, but discovering unique materials remains challenging due to the high cost of experimentation. In this study, machine learning models are employed to predict power conversion efficiency (PCE), Mordred descriptors are used for model training. Among the four machine learning models evaluated, the gradient boosting regressor emerged as the best-performing model. Additionally, a chemical library of polymer donors was generated and analyzed using various measures. 30 donors with highest PCE are selected and their synthetic accessibility is evaluated. Similarity analysis has indicated much resemblance in selected polymer donors.

A Fluorinated Imide-Functionalized Arene Enabling a Wide Bandgap Polymer Donor for Record-Efficiency All-Polymer Solar Cells.

All-polymer solar cells (all-PSCs) present compelling advantages for commercial applications, including mechanical durability and optical and thermal stability. However, progress in developing high-performance polymer donors has trailed behind the emergence of excellent polymer acceptors. In this study, we report a new electron-deficient arene, fluorinated bithiophene imide (F-BTI) and its polymer donor SA1, in which two fluorine atoms are introduced at the outer β-positions in the thiophene rings of BTI to fine-tune the energy levels and aggregation of the resulting polymers. SA1 exhibits a deep HOMO level of -5.51 eV, a wide bandgap of 1.81 eV and suitable miscibility with the polymer acceptor. Polymer chains incorporating F-BTI result in a highly ordered π-π stacking and favorable phase-separated morphology within the all-polymer active layer. Thus, SA1 : PY-IT-based all-PSCs exhibit an efficiency of 16.31 % with excellent stability, which is further enhanced to a record value of 19.33 % (certified: 19.17 %) by constructing ternary device. This work demonstrates that F-BTI offers an effective route for developing new polymer materials with improved optoelectronic properties, and the emergence of F-BTI will change the scenario in terms of developing polymer donor for high-performance and stable all-PSCs.

Quinoxaline based A-A Type Polymer Donors for Non-Fullerene Polymer Solar Cells

Quinoxaline based A-A Type Polymer Donors for Non-Fullerene Polymer Solar Cells

Terminal group engineering of oligothiophene donors for efficient organic solar cells

All-small-molecule organic solar cells exhibit high reproducibility than polymer-based cells. Benzodithiophene and oligothiophene based derivatives are the most widely studied small molecule donors. The lower synthetic complexity and superior stability make oligothiophene based derivatives more promising for large scale production. Recently, a thiazole-centered oligothiophene donor Tz6T yields a high efficiency but deserves further improving. Substitution of halogen atoms on the end groups is proven to affect molecular packing through various non-covalent intermolecular interactions. Here we adopt terminal group engineering to regulate the optoelectronic properties of Tz6T. Through chlorine substitution, highest efficiency (9.60 %) is achieved in Tz6T-PH-Cl-4: eC9-4F binary device. Our results shed light on the structure-function relationship, and provide valuable insights into the regulation of phase separation.

Design of Isoindigo-Based Small-Molecule Donors for Bulk Heterojunction Organic Solar Cell Applications in Combination with Nonfullerene Acceptors.

The development of small-molecule organic solar cells with the required efficiency depends on the information obtained from molecular-level studies. In this context, 39 small-molecule donors featuring isoindigo as an acceptor moiety have been meticulously crafted for potential applications in bulk heterojunction organic solar cells. These molecules follow the D2-A-D1-A-D2 and D2-A-π-D1-π-A-D2 framework. Similar molecules considered in the previous experimental study (molecules R1 ((3E,3″E)-6,6″-(benzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(1,1'-dimethyl-[3,3'-biindolinylidene]-2,2'-dione)) and R2 ((3E,3″E)-6,6″-(4,8-dimethoxybenzo[1,2-b:4,5-b']dithiophene-2,6-diyl)bis(1,1'-dimethyl-[3,3'-biindolinylidene]-2,2'-dione))) have been chosen as reference molecules. Molecules with and without π-spacers have been considered to understand the impact of the length of the π-spacer on intramolecular charge-transfer transitions and absorption properties. A detailed investigation is carried out to establish the relationship between the structure and photovoltaic parameters using density functional theory and time-dependent density functional theory methods. The newly developed molecules exhibit better electronic, excited-state, and charge transport properties than the reference molecules. Additionally, model donor-acceptor interfaces are constructed by integrating the designed donor molecules with fullerene/nonfullerene acceptors. The electronic and excited-state properties of these interfaces are rigorously evaluated. Results elucidate that the donor comprising of isoindigo-bithiophene-pyrroloindacenodithiophene (IIG-T2-PIDT) emerges as a promising candidate for bulk heterojunction solar cells based on nonfullerene acceptors. This research provides systematic design strategies for the development of small-molecule donors for organic solar cells.

Computational design and experimental investigation of novel thiophene-based organic dyes with N,N-dimethylaminophenyl and morpholinophenyl donors for dye-sensitized solar cells

A new series of thiophene-based organic chromophores (4–7 a, b) has been developed through structural engineering of the electron donor (D) group, incorporating N,N-dimethylaminophenyl and morpholinophenyl, and acceptor moieties such as benzonitrile and flurobenzonitrile. Additionally, a π-linkage of phenylthiophene was inserted. The effects of various donating and accepting groups, as well as the spacer, on the geometrical, energetic, absorption, and photovoltaic properties of these sensitizers were investigated using Density Functional Theory (DFT) and Time-Dependent DFT. The sensitizers were optimized in their ground state using selected functional methods. Furthermore, key properties such as absorbance, frequency, energies of Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO), energy gap, dipole moment, and global reactivity descriptors were calculated using quantum chemical calculations. These spectral properties and quantum chemical calculations provide valuable insights into the potential use of these sensitizers in photonic devices. The results obtained from analyzing light harvesting efficiency (LHE), free energy injection (ΔGinj), and open circuit voltage (Voc) demonstrate that these dyes show promising characteristics for future experimental studies and offer guidelines for improving the performance of dye-sensitized solar cells. By employing structural modifications and investigating the electronic properties of these newly developed chromophores, this study contributes to the understanding of their behavior and potential applications in photonic devices. The findings provide a foundation for further experimental investigations and offer valuable insights for the development of more efficient dye-sensitized solar cells.

Tetracyclic aromatic lactam-substituted tin-free donors for high-efficiency ternary organic solar cells via regulation of pre-aggregation and crystallization kinetics

Organic solar cells (OSCs) are rapidly developed for next-generation photovoltaic technologies due to low-cost and solution-processability etc. However, so far high-efficiency organic photovoltaic materials are typically prepared by multi-step Stille reactions, which are neither cost-efficient nor atom-economic, even raise safety concerns and incompatible with large-scale process. Large-scale industrial production of photovoltaic materials through simple, cost-effective, and green chemistry remains to be addressed. In this work, we present a case where two isomeric small-molecule donors based on polycyclic aromatic lactams (PAL) unit, named oPh2F and pPh2F with wide-bandgap and high-crystallinity, were designed and synthesized by atom-economic direct C-H activation strategy, modulates pre-aggregation and crystallization kinetics of host system PM6:Y6, induce distinct morphology evolution and effectively boost photovoltaic performance. The best power conversion efficiency (PCE) of 18.40 % for pPh2F-based ternary devices are found to be a fruit of improved light-harvesting ability, favorable vertical phase separation with enhanced crystallinity, the separated crystallization process of host materials and the higher and more balanced charge transport. To our knowledge, this study achieved the highest PCE among PM6:Y6-based ternary OSCs containing tin-free small-molecule donor, which not only highlights the great potential of PAL-based photovoltaic materials, but also promotes the integration of renewable energy with green chemistry.

Optimizing the film formation of high crystalline donors for efficient organic solar cells

The complex morphology regulation of the active layer of organic solar cells (OSCs) remains crucial for enhancing photovoltaic performance. However, understanding the transformation of solution aggregates to films under microstructure remains a challenging task. Reasonably introducing the third component guest is a simple and effective way to improve the molecular stacking and crystallinity of the active layer thin film. For this purpose, we designed and synthesized two highly crystalline polymer donors, D18-Si and D18-SiCl, and used them as the third component to improve molecular aggregation and induce crystallization. The results indicated that in the device with PM6:Y6 system, the OSC with D18-SiCl as the third component crystallization inducer obtains a power conversion efficiency (PCE) of 17.51%, which is significantly better than the PCE value of 16.03% of the control device. And a remarkable PCE of 18.67% is obtained in the ternary OSC based on the active layer of PM6: D18-SiCl: BTP-eC9. The achievement of excellent efficiency is mainly due to the optimization of film formation time, which prompted to the improvement of film morphology, thereby attributed to its higher exciton dissociation and charge transport. Our work provides a strategy for the in-depth study of the film-forming process of high-efficiency three-component.

Triselenasumanene-based organic molecules as donor and hole-transporting materials for next-generation solar cells

The optoelectronic and charge transport properties of triselenasumanene-based organic molecules were studied using electronic structure calculations to explore their potential as a hole-transporting material (HTM) in perovskite solar cells (PSCs) and as electron donors in organic solar cells (OSCs). Based on the recently synthesized triselenasumanene (SESUM) molecule, nine molecules (SESUMXn, where X = anthracene (A), tetracene (T) and pentacene (P), n = number of attached A, T and P, i.e. 1, 2 and 3) were designed by extending the π-conjugation. The newly designed molecules possessed suitable energy-level alignment with the energy bands of commonly used perovskite material, CH3NH3PbI3, in PSCs, and are suitable as electron-donor material with the commonly used acceptor material, PC61BM, in OSCs. The calculated ionic state properties and electrophilicity index also showed that the studied molecules were potential donor materials for OSCs. Further, the calculated open circuit voltage and fill factor of SESUM and anthracene- and tetracene-substituted SESUM molecules were comparable with those of recently reported donor molecules. The calculated absorption spectra, effective hole transfer integral and stacking angle distribution showed the suitability of SESUMX2 and SESUMX3 molecules as HTM in PSCs. The results of periodic density functional theory calculations showed that the tri-substituted SESUM molecules, SESUMX3 (where, X = A, T and P), were effectively adsorbed on the CH3NH3PbI3 surface and abstracted the hole carrier from the perovskite surface.

Terpolymer Containing a meta-Octyloxy-phenyl-Modified Dithieno[3,2-f:2',3'-h]quinoxaline Unit Enabling Efficient Organic Solar Cells.

With the rapid development of small-molecule electron acceptors, polymer electron donors are becoming more important than ever in organic photovoltaics, and there is still room for the currently available high-performance polymer donors. To further develop polymer donors with finely tunable structures to achieve better photovoltaic performances, random ternary copolymerization is a useful technique. Herein, by incorporating a new electron-withdrawing segment 2,3-bis(3-octyloxyphenyl)dithieno[3,2-f:2',3'-h]quinoxaline derivative (C12T-TQ) to PM6, a series of terpolymers were synthesized. It is worth noting that the introduction of the C12T-TQ unit can deepen the highest occupied molecular orbital energy levels of the resultant polymers. In addition, the polymer Z6 with a 10% C12T-TQ ratio possesses the highest film absorption coefficient (9.86 × 104 cm-1) among the four polymers. When blended with Y6, it exhibited superior miscibility and mutual crystallinity enhancement between Z6 and Y6, suppressed recombination, better exciton separation and charge collection characteristics, and faster hole transfer in the D-A interface. Consequently, the device of Z6:Y6 successfully achieved enhanced photovoltaic parameters and yielded an efficiency of 17.01%, higher than the 16.18% of the PM6:Y6 device, demonstrating the effectiveness of the meta-octyloxy-phenyl-modified dithieno[3,2-f:2',3'-h]quinoxaline moiety to build promising terpolymer donors for high-performance organic solar cells.

Miro1 improves the exogenous engraftment efficiency and therapeutic potential of mitochondria transfer using Wharton's jelly mesenchymal stem cells

Mitochondria are important for maintaining cellular energy metabolism and regulating cellular senescence. Mitochondrial DNA (mtDNA) encodes subunits of the OXPHOS complexes which are essential for cellular respiration and energy production. Meanwhile, mtDNA variants have been associated with the pathogenesis of neurodegenerative diseases, including MELAS, for which no effective treatment has been developed. To alleviate the pathological conditions involved in mitochondrial disorders, mitochondria transfer therapy has shown promise. Wharton's jelly mesenchymal stem cells (WJMSCs) have been identified as suitable mitochondria donors for mitochondria-defective cells, wherein mitochondrial functions can be rescued. Miro1 participates in mitochondria trafficking by anchoring mitochondria to microtubules. In this study, we identified Miro1 over-expression as a factor that could help to enhance the efficiency of mitochondrial delivery. More specifically, we reveal that Miro1 over-expressed WJMSCs significantly improved intercellular communications, cell proliferation rates, and mitochondrial membrane potential, while restoring mitochondrial bioenergetics in mitochondria-defective fibroblasts. Furthermore, Miro1 over-expressed WJMSCs decreased rates of induced apoptosis and ROS production in MELAS fibroblasts; although, Miro1 over-expression did not rescue mtDNA mutation ratios nor mitochondrial biogenesis. This study presents a potentially novel therapeutic strategy for treating mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), and other diseases associated with dysfunctional mitochondria, while the pathophysiological relevance of our results should be further verified by animal models and clinical studies.

Efficient triisopropylsilylethynyl-substituted benzo[1,2-b:4,5-b′]dithiophene-based random terpolymers enable non-fullerene organic solar cells with enhanced efficiency

Recent work has highlighted the pivotal role of ternary random polymers in the development of efficient high-performance polymer donors for organic solar cells (OSCs) and most of these D-A copolymer donors are so far constituted of an equal proportion of D and A-units. In this contribution, we report series of PM6-based ternary random terpolymers with unequal D- and A-units, namely, PM-TIPS10, PM-TIPS20 and PM-TIPS20, respectively by adding the 10%, 20% and 30% of simple and low-cost triisopropylsilylethynyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-TIPS) unit as second donor (D1) unit in polymer backbone based on D1-A-D2-A molecular design. Ascribed from the structural similarity of the two building blocks in the terpolymer backbone, these polymers showed orderly molecular packing, broadened light absorption, and the face-on orientation of the active layer to facilitate charge transport. Additionally, the new polymers displayed much deeper highest occupied molecular orbital (HOMO) energy levels than host PM6 polymer, which helped in enhancing the open circuit voltage (Voc) in the PM-TIPS-based OSCs. As a result, when combined with BTP-eC9 acceptor unit, PM-TIPS10 and PM-TIPS20 displayed best efficiency of 16.7 and 16.5% with a small energy loss of 0.484 and 0.473 eV, producing overall superior device parameters compared to PM6-based devices tested parallelly (PCE of 15.7%). This study reveals the correlation between introduction of the BDT-TIPS unit on polymer properties and photovoltaic performance and thus contributes to the design of high-PCE polymer donors by adapting a ternary random copolymerization strategy.

Fluorinated Polymer Donors for Nonfullerene Organic Solar Cells.

The rapid development of narrow-bandgap nonfullerene acceptors (NFAs) has boosted the efficiency of organic solar cells (OSCs) over 19 %. The new features of high-performance NFAs, such as visible-NIR light absorption, moderate the highest occupied molecular orbitals (HOMO), and high crystallinity, require polymer donors with matching physical properties. This emphasizes the importance of methods that can effectively tune the physical properties of polymers. Owning to very small atom size and strongest electronegativity, the fluorination has been proved the most efficient strategy to regulate the physical properties of polymer donors, including frontier energy level, absorption coefficient, dielectric constant, crystallinity and charge transport. Owing to the success of fluorination strategy, the vast majority of high-performance polymer donors possess one or more fluorine atoms. In this review, the fluorination synthetic methods, the synthetic route of well-known fluorinated building blocks, the fluorinated polymers which are categorized by the type of donor or acceptor units, and the relationships between the polymer structures, properties, and photovoltaic performances are comprehensively surveyed. We hope this review could provide the readers a deeper insight into fluorination strategy and lay a strong foundation for future innovation of fluorinated polymers.

Cyanoesterthiophene Based Low‐Cost Polymer Donors for High Efficiency Organic Solar Cells

AbstractTo achieve commercial application of organic solar cells (OSCs), it is necessary to reduce material costs and improve device efficiency. This paper reports on the utilization of a multifunctional building block, namely 3‐cyanoesterthiophene, which exhibits simple structure and accessibility of synthetic for cost‐effective and high‐performance polymer donors (PDs). Meanwhile, ternary and terpolymerization strategies have been studied. Two similar PDs, PBTCl0‐TCA and PBTCl100‐TCA, are synthesized, and the devices exhibit less‐than‐satisfactory efficiency of 13.21% and 11.53% due to mismatching energy level and imperfect morphology. The two PDs with comparable structures and commendable compatibility easily form alloy‐like phase in active layer, which can effectively boost the efficiency of ternary devices to 14.17% with retained high JSC and significant improved open‐circuit voltage (VOC) and fill factor (FF). Encouraged by the ternary blending phenomenon, a polymer donor (PBTCl50‐TCA) with same ratio by random terpolymerization is designed. And over 17% efficiency binary OSCs using terpolymerization donor are demonstrated. The synergies of incorporation of the cyanoester‐group and terpolymer endow the developed PDs with deep‐lying energy levels, face‐on orientation, thermodynamic miscibility with the prevailing nonfullerene acceptor and appropriate polymer crystallinity. The findings study provide valuable insights and support for the advancement of cost‐effective and high‐performance PDs.

Effect of Length of Ethylene Glycol Sigma‐Linkers on Triphenylamine‐Based Dimers Used as Molecular Donors for Organic Solar Cells

AbstractThe direct comparison of two push‐pull based dimers prepared in only three steps from commercially and affordable building blocks is reported herein. Built around similar absorbing units, two ethylene glycol sigma‐connectors of different lengths were used to investigate, and rationalize, their impact on the optical, self‐assembly and therefore photovoltaic properties. With significant differences from the charge transport, morphology and therefore power conversion efficiencies, results gathered in this study emphasized the potential of such simple yet efficient strategy to fine tune the processability of an active compound.

Design and virtual screening of donor and non-fullerene acceptor for organic solar cells using long short-term memory model

In this study, we trained long short-term memory models to predict photovoltaic performance parameters. Additionally, we cleaved and reorganized molecules to obtain novel high-performance donor–acceptor pairs.

Designing dithieno-benzodithiophene-based small molecule donors for thickness-tolerant and large-scale polymer solar cells

The small molecule donor SD62-doping strategy with an excellent universality is beneficial to fabricating thickness-tolerant and large-scale high-performance polymer solar cells and solar modules.

Carboxylic-substituted polymer design strategy enabled halogen-free solvent processed efficient organic solar cells

Carboxylic ester groups can be rationally utilized to regulate the energy levels and crystallinity in molecular design of conjugated polymer donors for organic solar cells (OSCs). In this work, a new polymer named PB4T was designed and prepared by copolymerization of a carboxylate substituted tetra-thiophene unit with the commonly used BDT unit. Due to the strong electron-withdrawing capability and the symmetric conformation of carboxylic ester substitution, PB4T exhibits appropriate HOMO energy level and stable planar geometry. When matching PB4T with five different NFAs with varied energy levels and bandgaps, including eC9, eC9-2Cl, IT-4F, BTA3, and A4T-3, all the OSCs processed with the halogen-free solvent show good photovoltaic performance. The PB4T:eC9- and PB4T:eC9-2Cl-based OSCs can realize high PCEs of 15.50 % and 15.32 %, respectively. This work demonstrates that PB4T has good universality to work well with newly-emerging NFAs, and carboxylate substituted thiophene units show great potential in constructing high-efficiency polymer donors.

Alkoxythiophene-Directed Fibrillization of Polymer Donor for Efficient Organic Solar Cells.

Realizing fibrillar molecular framework is highly encouraged in organic solar cells (OSCs) due to the merit of efficient charge carrier transport. This is however mainly achieved via the chemical structural design of photovoltaic semiconductors. In this work, through the utilization of three alkoxythiophene additives, T-2OMe, T-OEH, and T-2OEH, the intermolecular interactions among a series of BDT-type polymer donors, i.e., PM6, D18, PBDB-T, and PTB7-Th, are tuned to self-assemble into nanofibrils during solution casting. X-ray technique and molecular dynamics simulation reveal that the alkoxythiophene with (2-ethylhexyl)oxy (─OEH) chains can attach on the 2-ethylhexyl (EH) chains of these polymer donors and promote their self-assembly into 1D nanofibrils, in their neat films as well as photovoltaic blends with L8-BO. By adapting these fibrillar polymer donors to construct pseudo-bulk heterojunction (P-BHJ) OSCs via layer-by-layer deposition, generally improved device performance is seen, with power conversion efficiencies enhanced from 18.2% to 19.2% (certified 18.96%) and from 17.9% to 18.7% for the PM6/L8-BO and D18/L8-BO devices, respectively. This work provides a physical approach to promote the fibrillar charge transport channels for efficient photovoltaics.

18.6% Efficiency All-Polymer Solar Cells Enabled by a Wide Bandgap Polymer Donor Based on Benzo[1,2-d:4,5-d']bisthiazole.

The limited selection of wide bandgap polymer donors for all-polymer solar cells (all-PSCs) is a bottleneck problem restricting their further development and remains poorly studied. Herein, a new wide bandgap polymer, namely PBBTz-Cl, is designed and synthesized by bridging the benzobisthiazole acceptor block and chlorinated benzodithiophene donor block with thiophene units for application as an electron donor in all-PSCs. PBBTz-Cl not only possesses wide bandgap and deep energy levels but also displays strong absorption, high-planar structure, and good crystallinity, making it a promising candidate for application as a polymer donor in organic solar cells. When paired with the narrow bandgap polymer acceptor PY-IT, a fibril-like morphology forms, which facilitates exciton dissociation and charge transport, contributing to a power conversion efficiency (PCE) of 17.15% of the corresponding all-PSCs. Moreover, when introducing another crystalline polymer acceptor BTP-2T2F into the PBBTz-Cl:PY-IT host blend, the absorption ditch in the range of 600-750nm is filled, and the blend morphology is further optimized with the trap density reducing. As a result, the ternary blend all-PSCs achieve a significantly improved PCE of 18.60%, which is among the highest values for all-PSCs to date.