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Tuning the molecular packing and energy level of fullerene acceptors for polymer solar cells
摘要： Fullerenes are considered to be promising acceptor materials for fabrication of bulk-heterojunction polymer solar cells (PSCs) due to their excellent physical and chemical properties. Herein, two novel fullerene derivatives with different specific functional groups, 2-benzylthiophene-C60 bis-adduct (BTCBA) and 2-(4-methoxybenzyl)thiophene-C60 bis-adduct (MBTCBA), were synthesized and utilized as the acceptors for PSCs with the purpose of investigating the influence of the fullerene derivative substituents on the device performance. Compared with BTCBA, MBTCBA exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level due to the electron donating properties of the 2-(4-methoxybenzyl)thiophene functional group. Meanwhile, the appropriate intermolecular interaction of MBTCBA molecules promotes favorable nanophase separation of the P3HT/MBTCBA based blending film, resulting in higher electron mobility. Therefore, the PSCs incorporating P3HT as donor and MBTCBA as acceptor yield a power conversion efficiency (PCE) of 5.29% with an open-circuit voltage (VOC) of 0.81 V, which is obviously higher than that of BTCBA (3.54%) and PCBM (3.76%) based devices. Our work proves that the PSCs performance can be readily improved by modification of fullerene acceptors using electron donating group, tuning the LUMO energy level and the molecular packing behavior.
关键词： Bis-adduct fullerene derivatives,Fullerenes,LUMO energy level,Molecular packing,Polymer solar cells
更新于2025-09-11 14:15:04
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Optimizing domain size and phase purity in all-polymer solar cells by solution order aggregation and confinement effect of the acceptor
摘要： Domain size, phase purity, and the interpenetrating network within the active layer of all-polymer solar cells (all-PSCs) are crucial for efficient charge generation and carrier transport. However, it is a great challenge to decrease domain size and enhance phase purity simultaneously because of the energetically disfavoring polymer-polymer mixing and chain entanglement. In this work, we manipulated the domain size and phase purity of J51:N2200 blends by promoting their solution ordered aggregation and the confinement of acceptor N2200 to J51 during phase separation. Thus, three solvents, chloroform (CF), mesitylene (Mes), and cyclopentyl methyl ether (CPME) were selected. The solubility of J51 and N2200 in these three solvents decreases solubility differences between J51 and N2200 increases gradually. Among these three solvents, only in CPME solution, N2200 possesses ordered structures, which reduces nucleation barrier to increase nucleation density and boosts template effect of N2200. During phase separation, the ordered aggregation of N2200 dominates solid-liquid phase separation and has the confinement effect of J51. Thus, the blend films cast from CPME have fine-scale phase separation in contrast to the films from CF. In addition, the "memory" effect of ordered aggregations transferred to films can enforce the order of blend films. As a result, the blend film with small domain size (≈21 nm), interpenetrating network structure, and a higher degree of crystallinity was obtained by processed from green solvent CPME. The improved morphology facilitated charge-generating process and carrier transport, resulting in higher short-circuit current (Jsc), fill factor (FF), and the power conversion efficiency (PCE).
关键词： all-polymer solar cells,domain size,phase purity,solution ordered aggregation,confinement effect
更新于2025-09-11 14:15:04
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Small Band gap Boron Dipyrromethene-Based Conjugated Polymers for All-Polymer Solar Cells: The Effect of Methyl Units
摘要： Naphthalene diimide (NDI)-based conjugated polymers have been widely used as the nonfullerene electron acceptor for all-polymer solar cells (all-PSCs), but their low absorption coefficient in the near-infrared (NIR) region severely limits the light harvesting ability in solar cells and hence lowers their photovoltaic performance. In this work, two narrow band gap donor?acceptor conjugated polymers based on boron dipyrromethene (BODIPY) as the electron-deficient unit were developed as the electron donor to combine with a NDI-polymer acceptor in order to significantly improve the photoresponse in the NIR region. More importantly, we found that methyl substitution on the BODIPY segment played an important role in charge transport in these polymers. When methyl units were attached to the α-position of BODIPY, the polymer PMBBDT exhibited high-lying energy levels, improved crystallinity, and dramatically high hole mobility compared to the polymer PBBDT without methyl substitution. Consequently, the power conversion efficiencies (PCEs) could be enhanced from 0.32% for PBBDT- to 5.8% for PMBBDT-based all-PSCs, and the photoresponse covered from 300 to 900 nm. Our results demonstrate that methyl-substituted BODIPY-based conjugated polymers are promising candidates to solve the NIR absorption issue in NDI polymers and, therefore, can be potentially used to further boost the PCEs of all-PSCs similar with organic solar cells based on NIR-fused ring electron acceptors.
关键词： Boron dipyrromethene,Methyl substitution,Conjugated polymers,Near-infrared absorption,All-polymer solar cells
更新于2025-09-11 14:15:04
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A distorted lactam unit with intramolecular hydrogen bonds as the electron donor of polymer solar cells
摘要： A novel distorted lactam motif, namely 4,40-dialkyl-[6,60-bithieno[3,2-b]pyridine]-5,50(4H,40H)-dione (BTP), could lock itself by intramolecular hydrogen bonds. In view of the potential of the motif, two D–A conjugated polymers, PBDT-BTP-HD and PBDT-BTP-OD, with two different long side chains consisting of 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b0]dithiophene (BDT) as a donor unit and BTP as an acceptor unit were designed and synthesized. Furthermore, the photophysical, electrochemical and photovoltaic properties of both polymers were investigated. The morphologies and molecular ordering of the neat polymers and blend films were also probed to relate the side chain structures with aggregation states and device parameters. The device based on PBDT-BTP-OD with IT-M exhibited a power conversion efficiency of up to 9.54% thanks to the synergistic effect of the building blocks and side-chain engineering. As a result, it is successfully demonstrated that the novel distorted lactam BTP is a promising building block in organic solar cells.
关键词： side-chain engineering,intramolecular hydrogen bonds,electron donor,distorted lactam,polymer solar cells
更新于2025-09-11 14:15:04
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Toxic Solvent‐ and Additive‐Free Efficient All‐Polymer Solar Cells via a Simple Random Sequence Strategy in Both Donor and Acceptor Copolymer Backbones
摘要： It is extremely important to develop nontoxic solvent and additive-processed high-performance all-polymer solar cells (all-PSCs) that are suitable for printing preparation of large-scale devices. Herein, it is demonstrates that a simple random copolymerization of two acceptor monomers (benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) and 5,6-difluoro-2H-benzo[d][1,2,3] triazole (FTAZ)), alternating with Si atom-containing benzo[1,2-b:4,5-b′] dithiophene donor comonomer, forms a successful approach by which to synthesize donor copolymers with excellent solubility/processability for nontoxic-solvent-processed all-PSCs. The incorporation of a higher degree of BDD in the backbone lowers the frontier energy levels, as well as redshifts, with higher absorption coefficients; however, it adversely affects solubility in a 2-methyltetrahydrofuran (MeTHF). An impressive power conversion efficiency, of about 8.0%, is achieved from PJ25 (25 mol% BDD)-based all-PSC when paired with N2200-F30 acceptor random copolymer by using MeTHF as the processing solvent without any additive. Another interesting point is that the air stability of the all-PSCs increases with increasing FTAZ content due to strong noncovalent interaction and resistance to humidity and oxidation caused by the F-atoms in FTAZ units. Not only does this study establish a structure–property–performance relationship through a series of structural, morphological, and electrical characterization techniques, but it also provides a promising and easy way to develop nontoxic-solvent-processed high-performance all-PSCs.
关键词： compatibility,nontoxic solvents,random copolymers,additive-free processing,all-polymer solar cells
更新于2025-09-11 14:15:04
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Comparative study on the effects of alkylsilyl and alkylthio side chains on the performance of fullerene and non-fullerene polymer solar cells
摘要： Two novel high gap donor polymers – PBDTTSi-TzBI and PBDTTS-TzBI, based on imide fused benzotriazole (TzBI) with asymmetric side chains and alkylsilyl (Si) or alkylthio (S) substituted 4,8-di(thien-2-yl)benzo[1,2-b:4,5-b′]dithiophene (BDTT) – are successfully synthesized. The effect of the side chain variation on the photophysical, morphological and photovoltaic properties of blends of these polymers with fullerene and non-fullerene acceptors is investigated. The PBDTTSi-TzBI polymer shows a deeper highest occupied molecular orbital energy level, which results in higher open-circuit voltages. Nevertheless, the polymer solar cells fabricated using PBDTTS-TzBI in combination with PC71BM afford a higher power conversion efficiency of 7.3% (vs 4.0% for PBDTTSi-TzBI:PC71BM). By using the non-fullerene acceptor ITIC, the absorption of the blends extends to 850 nm and better device efficiencies are achieved, 6.9% and 9.6% for PBDTTSi-TzBI:ITIC and BDTTS-TzBI:ITIC, respectively. The better performance for PBDTTS-TzBI:ITIC is attributed to the strong and broad absorption and balanced charge transport, and is among the best so far for non-fullerene solar cells based on TzBI-containing polymer donors.
关键词： Alkylthio,Benzotriazole,Alkylsilyl,Polymer solar cells,Non-fullerene acceptors,Photovoltaic properties
更新于2025-09-11 14:15:04
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Ambient Processable and Stable All-Polymer Organic Solar Cells
摘要： In this work, the way in which ambient moisture impacts the photovoltaic performance of conventional PCBM and emerging polymer acceptor–based organic solar cells is examined. The device performance of two representative p-type polymers, PBDB-T and PTzBI, blended with either PCBM or polymeric acceptor N2200, is systemically investigated. In both cases, all-polymer photovoltaic devices processed from high-humidity ambient conditions exhibit significantly enhanced moisture-tolerance compared to their polymer–PCBM counterparts. The impact of moisture on the blend film morphology and electronic properties of the electron acceptor (N2200 vs PCBM), which results in different recombination kinetics and electron transporting properties, are further compared. The impact of more comprehensive ambient conditions (moisture, oxygen, and thermal stress) on the long-term stability of the unencapsulated devices is also investigated. All-polymer solar cells show stable performance for long periods of storage time under ambient conditions. The authors believe that these findings demonstrate that all-polymer solar cells can achieve high device performance with ambient processing and show excellent long-term stability against oxygen and moisture, which situate them in an advantageous position for practical large-scale production of organic solar cells.
关键词： recombination,long-term air stability,all-polymer solar cells,ambient processability
更新于2025-09-11 14:15:04
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A non-fullerene acceptor based on alkylphenyl substituted benzodithiophene for high efficiency polymer solar cells with a small voltage loss and excellent stability
摘要： In this work, a new non-fullerene small molecule acceptor (NF-SMA) named BP-4F, based on benzo[1,2-b:4,5-b’]di(cyclopenta[2,1-b:3,4-b’]dithiophene) with 4-(2-ethylhexyl)phenyl conjugated side chains (BDT-P) as an electron-donating core, flanked with the strong electron-withdrawing 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)-malononitrile (2FIC) unit, is designed and synthesized for polymer solar cells application. BP-4F exhibits strong absorption in the 550 to 830 nm region with a narrow optical band gap of 1.49 eV, suitable energy levels with a lowest unoccupied molecular orbital (LUMO) of -3.90 eV and an effective electron mobility of 2.10×10-4 cm2 V-1 s-1. When blended with the wide bandgap polymer PM6 as the active layer, the polymer solar cells (PSCs) achieve an average power conversion efficiency (PCE) of 13.9% with an energy loss (Eloss) as low as 0.59 eV, which is of benefit to overcome the trade-off between Jsc and Voc. Furthremore, the BP-4F-based PSCs achieve an excellent PCE of 12.3% with a device area of 1.10 cm2. Notably, the devices show an excellent storage stability and photo-stability with retaining near 90% of the initial PCE in air under dark and 93.5% in glovebox under continuous illumination for 720 hours, respectively. These results indicate that BP-4F is an effective electron acceptor for high efficiency and stable polymer solar cells.
关键词： PM6,polymer solar cells,energy loss,stability,BP-4F,non-fullerene small molecule acceptor
更新于2025-09-11 14:15:04
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Self-doping small molecular conjugated electrolytes enabled by n-type side chains for highly efficient non-fullerene polymer solar cells
摘要： We developed a series of novel small molecular conjugated electrolytes (SMCEs) via side chain engineering. The introduced n-type 1,3,4-thiadiazole/1,3,4-oxadiazole side chains featured the related SMCEs with self-doping nature and high electron conductive property. On using as cathode interlayers in non-fullerene-polymer solar cells, a high power conversion efficiency (PCE) of up to 13.21% was achieved with an excellent thickness-insensitive property.
关键词： thickness-insensitive property,side chain engineering,power conversion efficiency,non-fullerene polymer solar cells,small molecular conjugated electrolytes
更新于2025-09-11 14:15:04
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Effects of Monofluorinated Positions at the End-Capping Groups on the Performances of Twisted Non-Fullerene Acceptor-Based Polymer Solar Cells
摘要： Recently, the main-chain twisted small molecules are attractive as electron-acceptors in polymer solar cells (PSCs) for their up-shifted molecular energy levels, enhanced extinction coefficients, better charge extraction properties along with longer carrier lifetime and lower recombination rate relative to their planar analogues, which are conducive to the power conversion efficiency (PCE) promotion of PSCs. To further probe the ‘structure-performance’ correlation of main-chain twisted acceptors, in particular the mono-fluorine substituted sites on the performances of the resultant acceptors, two new main-chain twisted small molecules were synthesized, in which a fluorine atom was introduced at different sites on the end-capping group 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN). Although finely structural modification was adopted, quite different performances were obtained in the two acceptors. Compared to the 3-fluorinated analogue (i-IEICO-F3), the mixture of 4-florinated and 5-fluorinated isomers (i-IEICO-2F) exhibited higher dipole moment, enlarged molar extinction coefficient with bathochromic-shifted absorption region, suppressed charge recombinations with balanced charge mobilities, and slightly enhanced crystallinity. In combination with a fluorobenzotriazole-based medium-bandgap polymer (J52), a high efficiency of 12.86% was resultantly achieved in i-IEICO-2F-based device, which is superior to the result (7.65%) of i-IEICO-F3 device, revealing the importance of mono-fluorinated positions on the performances of main-chain twisted non-fullerene acceptors.
关键词： Power conversion efficiency,Fluorinated position effects,Main-chain twisted small molecular acceptors,Polymer solar cells,Non-fullerene acceptors
更新于2025-09-11 14:15:04