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1.
In this work, sidechain engineering on conjugated fused‐ring acceptors for conformation locking is demonstrated as an effective molecular design strategy for high‐performance nonfullerene organic solar cells (OSCs). A novel nonfullerene acceptor (ITC6‐IC) is designed and developed by introducing long alkyl chains into the terminal electron‐donating building blocks. ITC6‐IC has achieved definite conformation with a planar structure and better solubility in common organic solvents. The weak electron‐donating hexyl upshifts the lowest unoccupied molecular orbital level of ITC6‐IC, resulting in a higher VOC in comparison to the widely used ITIC. The OSCs based on PBDB‐T:ITC6‐IC reveal a promising power conversion efficiency of 11.61% and an expected high VOC of 0.97 V. The weaker π–π stacking induced by steric hindrance affords ITC6‐IC with enhanced compatibility with polymer donors. The blend film treated with suitable thermal annealing exhibits a fibril crystallization feature with a good bicontinuous network morphology. The results indicate that the molecular design approach of ITC6‐IC can be inspirational for future development of nonfullerene acceptors for high efficiency OSCs.  相似文献   

2.
A novel Ru π‐expanded terpyridyl sensitizer, referred to as HIS‐2, is prepared based on the molecular design strategy of substitution with a moderately electron‐donating 4‐methylstyryl group onto the terpyridyl ligand. The HIS‐2 dye exhibits a slightly increased metal‐to‐ligand charge transfer (MLCT) absorption at around 600 nm and an intense π–π* absorption in the UV region compared with a black dye. Density functional theory calculations reveal that the lowest unoccupied molecular orbital (LUMO) is distributed over the terpyridine and 4‐methylstyryl moieties, which enhances the light‐harvesting capability and is appropriate for smooth electron injection from the dye to the TiO2 conduction band. The incident photon‐to‐electricity conversion efficiency spectrum of HIS‐2 exhibits better photoresponse compared with black dye over the whole spectral region as a result of the extended π‐conjugation. A DSC device based on black dye gives a short‐circuit current (JSC) of 21.28 mA cm?2, open‐circuit voltage (VOC) of 0.69 V, and fill factor (FF) of 0.72, in an overall conversion efficiency (η) of 10.5%. In contrast, an HIS‐2 based cell gives a higher JSC value of 23.07 mA cm?2 with VOC of 0.68 V, and FF of 0.71, and owing to the higher JSC value of HIS‐2, an improved η value of 11.1% is achieved.  相似文献   

3.
Two non-fullerene small molecule acceptors (TFQ-F and TFQ-Cl) based on quinoxaline unit were designed and synthesized for efficient organic solar cells (OSCs). These two acceptors showed intense absorption up to 900 nm and high thermal stabilities with decomposition temperatures over 360 °C due to their fused-ring skeletons. TFQ-F and TFQ-Cl are the A-D-A′-D-A type acceptors (A/A′ for acceptor unit and D for donor unit). TFQ-F and TFQ-Cl have the same D-A′-D fragment, which was flanked with different ending groups. The effect of different ending groups on their photophysical properties, electrochemical behaviors, micro-structures and charge recombination properties of active layers, and device performance were investigated systematically. PM6 with the complementary absorption to the two acceptors was used as the donor material. The pristine PM6:TFQ-F blend films displayed the optimal morphologies as revealed by AFM and TEM measurement. Organic solar cells based on PM6:TFQ-Cl blend film showed high JSC of 25.19 mA/cm2 and PCE of 13.2%. The Voc, JSC and PCE for PM6:TFQ-F film based device were 0.857 V, 23.70 mA/cm2 and 13.51%, respectively. The dependence of VOC/JSC on various light intensities indicated that PM6:TFQ-F/Cl based device had low charge recombination.  相似文献   

4.
The elaborate balance between the open-circuit voltage (VOC) and the short-circuit current density (JSC) is critical to ensure efficient organic solar cells (OSCs). Herein, the chalcogen containing branched chain engineering is employed to address this dilemma. Three novel nonfullerene acceptors (NFAs), named BTP-2O , BTP-O-S , and BTP-2S , featuring different peripheral chalcogen containing branched chains are synthesized. Compared with symmetric BTP-2O and BTP-2S grafting two alkoxy or alkylthio branched chains, the asymmetric BTP-O-S grafting one alkoxy and one alkylthio branched chains shows mediate absorption range, applicable miscibility, and favorable crystallinity. Benefiting from the enhanced π–π stacking and charge transport, an optimal power conversion efficiency (PCE) of 17.3% is obtained for the PM6: BTP-O-S -based devices, with a good balance between VOC (0.912 V) and JSC (24.5 mA cm−2), and a high fill factor (FF) of 0.775, which is much higher than those of BTP-2O (16.1%) and BTP-2S -based (16.4%) devices. Such a result represents one of the highest efficiencies among the binary OSCs with VOC surpassing 0.9 V. Moreover, the BTP-O-S -based devices fabricated by using green solvent yield a satisfactory PCE of 17.1%. This work highlights the synergistic effect of alkoxy and alkylthio branched chains for high-performance OSCs by alleviating voltage loss and enhancing FF.  相似文献   

5.
The contradiction between enlarging the offset between energy levels of donor/acceptor and the required driving force for exciton split leads to a trade‐off between open circuit voltage (VOC) and short circuit current density (JSC), which is a big challenge for development of high performance polymer solar cells (PSCs). Some advanced works reported the PSCs with low photon energy loss (Eloss) and small driving force, but the correlation of molecular structures of light‐harvesting system and driving force is still unclear. In this work, a new alkylsilyl functionalized copolymer donor PBDS‐T (PBDST: poly[(2,6trialkylsilyl thiophen2yl)benzo[1,2b:4,5b′]dithiophene))alt(5,5(1′,3′di2thienyl5′,7′bis(2ethylhexyl)benzo[1′,2′c:4′,5′c′]dithiophene4,8dione))]) with low‐lying energy levels was designed for efficient PSCs. By monitoring the Photoluminescence quenching of the bulk and bilayer heterojunctions, small driving forces, ?EHOMO of 0.15 eV and ?ELUMO of 0.22 eV were founded to allow for efficient charge transfer, which were observed to correlate with the crystalline PBDS‐T and the optimal morphology in PBDS‐T:ITIC (ITIC: 3,9bis(2methylene(3(1,1dicyanomethylene)indanone))5,5,11,11tetrakis(4hexylphenyl)dithieno[2,3d:2′,3′d′]sindaceno[1,2b:5,6b′]dithiophene). Simultaneously improved VOC, JSC and small Eloss boosted the PCE over 11%, which is one of the highest values for annealing‐free device. These results shield a light on precise design of a light‐harvesting system with small driving force to simultaneously improve the VOC and JSC for highly efficient PSCs.  相似文献   

6.
One of the most promising approaches to achieve high‐performance polymer solar cells (PSCs) is to develop nonfullerene small molecule acceptors (SMAs) with an absorption extending to the near‐infrared (NIR) region. In this work, two novel SMAs, namely, BTTIC and BTOIC, are designed and synthesized, with optical bandgaps (Egopt) of 1.47 and 1.39 eV, respectively. Desipte the narrow Egopt, the PBDB‐T:BTTIC‐ and PBDB‐T:BTOIC‐based PSCs can maintain high VOCs of over 0.90 and 0.86 V, respectively, with low energy losses (Eloss) < 0.6 eV. Meanwhile, due to the favorable morphology of the PBDB‐T:BTTIC blend, balanced carrier mobilities are achieved. The high external quantum efficiencies enable a high power conversion efficiency (PCE) up to 13.18% for the PBDB‐T:BTTIC‐based PSCs. In comparison, BTOIC shows an excessive crystallization propensity owing to its oxyalkyl side groups, which eventually leads to a relatively low PCE for the PBDB‐T:BTOIC‐based PSCs. Overall, this work provides insights into the design of novel NIR‐absorbing SMAs for nonfullerene PSCs.  相似文献   

7.
In recent years, tremendous progresses have been achieved for solution processed organic solar cells (OSCs). The strategy of adding a third component to fabricate ternary solar cells has emerged as an effective method to enhance the power conversion efficiency (PCE) of devices. Furthermore, small molecules feature as lower viscosity and excellent repeatability which facilitate the effective morphology control during fabrication process for enhanced photovoltaic performance. Herein, we report a series of ternary solar cells based on a liquid crystal molecule BTR and two electron acceptors of PC71BM and Y6. These molecules show complementary absorption to broaden spectra coverage and form energy levels cascade for efficient charge transfer. Meanwhile, thanks to the improved molecular packing and formed efficient charge transport network in the ternary blend film, the optimal ternary device possesses the improved charge dynamics and suppressed charge recombination. Thus, ternary solar cells deliver the highest PCE of 11.82% with simultaneously enhanced parameters of JSC, VOC and FF. This finding further illustrates the important roles of synergistic effect of fullerenes and non-fullerene acceptors in fabricating highly efficient ternary solar cells.  相似文献   

8.
Organic solar cells (OSCs) consisting of an ultralow‐bandgap nonfullerene acceptor (NFA) with an optical absorption edge that extends to the near‐infrared (NIR) region are of vital interest to semitransparent and tandem devices. However, huge energy‐loss related to inefficient charge dissociation hinders their further development. The critical issues of charge separation as exemplified in NIR‐NFA OSCs based on the paradigm blend of PTB7–Th donor (D) and IEICO–4F acceptor (A) are revealed here. These studies corroborate efficient charge transfer between D and A, accompanied by geminate recombination of photo‐excited charge carriers. Two key factors restricting charge separation are unveiled as the connection discontinuity of individual phases in the blend and long‐lived interfacial charge‐transfer states (CTS). By incorporation of a third‐component of benchmark ITIC or PC71BM with various molar ratios, these two issues are well‐resolved accordingly, yet in distinctly influencing mechanisms. ITIC molecules modulate film morphology to create more continuous paths for charge transportation, whereas PC71BM diminishes CTS and enhances electron transfer at the D/A interfaces. Consequently, the optimal untreated ternary OSCs comprising 0.3 wt% ITIC and 0.1 wt% PC71BM in the blend deliver higher JSC values of 21.9 and 25.4 mA cm‐2, and hence increased PCE of 10.2% and 10.6%, respectively.  相似文献   

9.
Three asymmetric non-fullerene acceptors (LL2, LL3, and LL4) are designed and synthesized with one norbornyl-modified 1,1-dicyanomethylene-3-indanone (CBIC) terminal group and one chlorinated 1,1-dicyanomethylene-3-indanone (IC-2Cl) terminal group. The three-dimensional shape-persistent CBIC terminal group can effectively enhance the solubility and tune the packing mode of acceptors. Compared with their symmetric counterparts (LL2-2Cl, LL3-2Cl, and LL4-2Cl) bearing two IC-2Cl terminals, the asymmetric acceptors show improved solubilities, giving rise to enhanced crystallinity and favored nanomorphology for charge transport in the blend films with PBDB-T. Asymmetric acceptors based organic solar cells (OSCs) also show much lower voltage loss due to their higher ECT and EQEEL values. Therefore, they exhibit 17−27% higher power conversion efficiency (PCE) than OSCs based on the corresponding symmetric acceptors. Among these six acceptors, LL3 with a central benzotriazole core shows the best PCE of 16.82% with an outstanding Jsc of 26.97 mA cm−2 and a low nonradiative voltage loss (ΔVnr) of 0.18 V, the best values for PBDB-T based OSCs. The Jsc and ΔVnr also represent the best reported for asymmetric non-fullerene acceptors-based OSCs to date. The results demonstrate that the combination of the unique CBIC terminal group with the asymmetric strategy is a promising way to enhance the performance of OSCs.  相似文献   

10.
Introducing a third component into organic bulk heterojunction solar cells has become an effective strategy to improve photovoltaic performance. Meanwhile, the rapid development of non-fullerene acceptors (NFAs) has pushed the power conversion efficiency (PCE) of organic solar cells (OSCs) to a higher standard. Herein, a series of fullerene-free ternary solar cells are fabricated based on a wide bandgap acceptor, IDTT-M, together with a wide bandgap donor polymer PM6 and a narrow bandgap NFA Y6. Insights from the morphological and electronic characterizations reveal that IDTT-M has been incorporated into Y6 domains without disrupting its molecular packing and sacrificing its electron mobility and work synergistically with Y6 to regulate the packing pattern of PM6, leading to enhanced hole mobility and suppressed recombination. IDTT-M further functions as an energy-level mediator that increases open-circuit voltage (VOC) in ternary devices. In addition, efficient Förster resonance energy transfer (FRET) between IDTT-M and Y6 provides a non-radiative pathway for facilitating exciton dissociation and charge collection. As a result, the optimized ternary device features a significantly improved PCE up to 16.63% with simultaneously enhanced short-circuit current (JSC), VOC, and fill factor (FF).  相似文献   

11.
Small‐molecule acceptors (SMAs)‐based organic solar cells (OSCs) have exhibited great potential for achieving high power conversion efficiencies (PCEs). Meanwhile, developing asymmetric SMAs to improve photovoltaic performance by modulating energy level distribution and morphology has drawn lots of attention. In this work, based on the high‐performance SMA (Y6), three asymmetric SMAs are developed by substituting the fluorine atoms on the terminal group with chlorine atoms, namely SY1 (two F atoms and one Cl atom), SY2 (two F atoms and two Cl atoms), and SY3 (three Cl atoms). Y6 (four F atoms) and Y6‐4Cl (four Cl atoms) are synthesized as control molecules. As a result, SY1 exhibits the shallowest lowest unoccupied molecular orbital energy level and the best molecular packing among these five acceptors. Consequently, OSCs based on PM6:SY1 yield a champion PCE of 16.83% with an open‐circuit voltage (VOC) of 0.871 V, and a fill factor (FF) of 0.760, which is the best result among the five devices. The highest FF for the PM6:SY1‐based device is mainly ascribed to the most balanced charge transport and optimal morphology. This contribution provides deeper understanding of applying asymmetric molecule design method to further promote PCEs of OSCs.  相似文献   

12.
Interdigitated back contact silicon heterojunction (IBC‐SHJ) solar cells have the potential for high open circuit voltage (VOC) due to the surface passivation and heterojunction contacts, and high short circuit current density (JSC) due to all back contact design. Intrinsic amorphous silicon (a‐Si:H) buffer layer at the rear surface improve the surface passivation hence VOC and JSC, but degrade fill factor (FF) from an “S” shape JV curve. Two‐dimensional (2D) simulation using “Sentaurus device” demonstrates that the low FF is related to the valence band offset (energy barrier) at the hetero‐interface. Three approaches to the buffer layer are suggested to improve the FF: (1) reduced thickness, (2) increased conductivity, and/or (3) reduced band gap. Experimental IBC‐SHJ solar cells with reduced buffer thickness (<5 nm) and increased conductivity with low boron doping significantly improves FF, consistent with simulation. However, this has only marginal effect on efficiency since JSC and VOC also decrease due to poor surface passivation. A narrow band gap a‐Si:H buffer layer improves cell efficiency to 13.5% with unoptimized passivation quality. These results demonstrate that tailoring the hetero‐interface band structure is critical for achieving high FF. Simulations predicts that efficiences >23% are possible on planar devices with optimized pitch dimensions and achievable surface passivation, and 26% with light trapping. This work provides criterion to design IBC‐SHJ solar cell structures and optimize cell performance. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
Four acceptor1-acceptor2-donor-acceptor2-acceptor1 (A1-A2-D-A2-A1) structural electron acceptors with different end-chains were designed and synthesized which all possessed indacenodithiophene (IDT) core, benzothiadiazole (BT) bridge as acceptor2, and rhodanine (R) end groups as acceptor1. The non-fullerene acceptor attached with ethyl group is called IDT-BT-R2 and used as control compound. And the other three of them are attached with methoxymethyl, trifluoroethyl and 1-piperidino groups generating IDT-BT-RO, IDT-BT-RF3 and IDT-BT-RN, respectively. The influence of end-chains on their optoelectronic properties were compared between four non-fullerene acceptors. Compared with IDT-BT-R2, the molecule IDT-BT-RF3 show red-shifted light absorption and lower LUMO level because of the electron withdrawing property of fluorine atoms. OSCs based on IDT-BT-RF3 display more efficient charge separation and lower degree of monomolecular recombination, allowing OSCs to show higher short-circuit current (Jsc) than the system of IDT-BT-R2. OSCs based on IDT-BT-RO also show more efficient charge separation and less monomolecular recombination. Due to the elevated LUMO level of the acceptor IDT-BT-RN, organic solar cells (OSCs) utilizing this material as acceptor display high open-circuit voltage (Voc) of 1.10 eV and low energy loss of 0.49 eV when maintaining a relatively high power conversion efficiency (PCE) of 7.09%. We demonstrated that the end-chain engineering could finely tune the light absorption properties and energy levels of novel non-fullerene acceptors and eventually improved OSCs performance can be harvested.  相似文献   

14.
A new class of thiocyanate‐free Ru(II) sensitizers with 4,4′‐dicarboxyvinyl‐2,2′‐bipyridine anchor and two trans‐oriented pyrid‐2‐yl pyrazolate (or triazolate) functional chromophores is synthesized, characterized, and evaluated in dye‐sensitized solar cells (DSCs). Despite their enhanced red response and absorptivity when compared to the parent sensitizer TFRS‐2 that possesses standard 4,4′‐dicarboxyl‐2,2′‐bipyridine anchor and shows the best conversion efficiency of η = 9.82%, the newly synthesized carboxyvinyl‐pyrazolate sensitizers, TFRS‐11 – TFRS‐13 , exhibit inferior performance characteristics in terms of short‐circuit current density (JSC), open‐circuit voltage (VOC), and power conversion efficiency (η), the latter being recorded to be in the range 5.60–7.62%. The reduction in device efficiencies is attributed to a combination of poor packing of these sensitizers on the TiO2 surface and less positive ground‐state oxidation potentials, which, respectively, increase charge recombination with I3? in electrolytes and impede the regeneration of sensitizers by I? anions. The latter obstacle can be circumvented in part by the replacement of the pyrazolates with triazolates, forming the TFRS‐14 sensitizer, which exhibits an improved JSC, VOC, and η of 16.4 mAcm?2, 0.77 V, and 9.02%, respectively.  相似文献   

15.
Understanding the factors that limit the performance of perovskite solar cells (PSCs) can be enriched by detailed temperature (T)‐dependent studies. Based on p‐i‐n type PSCs with prototype methylammonium lead triiodide (MAPbI3) perovskite absorbers, T‐dependent photovoltaic properties are explored and negative T‐coefficients for the three device parameters (VOC, JSC, and FF) are observed within a wide low T‐range, leading to a maximum power conversion efficiency (PCE) of 21.4% with an impressive fill factor (FF) approaching 82% at 220 K. These T‐behaviors are explained by the enhanced interfacial charge transfer, reduced charge trapping with suppressed nonradiative recombination and narrowed optical bandgap at lower T. By comparing the T‐dependent device behaviors based on MAPbI3 devices containing a PASP passivation layer, enhanced PCE at room temperature is observed but different tendencies showing attenuating T‐dependencies of JSC and FF, which eventually leads to nearly T‐invariable PCEs. These results indicate that charge extraction with the utilized all‐organic charge transporting layers is not a limiting factor for low‐T device operation, meanwhile the trap passivation layer of choice can play a role in the T‐dependent photovoltaic properties and thus needs to be considered for PSCs operating in a temperature‐variable environment.  相似文献   

16.
Ternary polymer solar cells (PSCs) are one of the most promising device architectures that maintains the simplicity of single‐junction devices and provides an important platform to better tailor the multiple performance parameters of PSCs. Herein, a ternary PSC system is reported employing a wide bandgap polymeric donor (PBTA‐PS) and two small molecular nonfullerene acceptors (labeled as LA1 and 6TIC). LA1 and 6TIC keep not only well‐matched absorption profiles but also the rational crystallization properties. As a result, the optimal ternary PSC delivers a state of the art power conversion efficiency (PCE) of 14.24%, over 40% higher than the two binary devices, resulting from the prominently increased short‐circuit current density (Jsc) of 22.33 mA cm?2, moderate open‐circuit voltage (Voc) of 0.84 V, and a superior fill factor approaching 76%. Notably, the outstanding PCE of the ternary PSC ranks one of the best among the reported ternary solar cells. The greatly improved performance of ternary PSCs mainly derives from combining the complementary properties such as absorption and crystallinity. This work highlights the great importance of the rational design of matched acceptors toward highly efficient ternary PSCs.  相似文献   

17.
The performance of all‐polymer solar cells (all‐PSCs) is often limited by the poor exciton dissociation process. Here, the design of a series of polymer donors ( P1 – P3 ) with different numbers of fluorine atoms on their backbone is presented and the influence of fluorination on charge generation in all‐PSCs is investigated. Sequential fluorination of the polymer backbones increases the dipole moment difference between the ground and excited states (Δµge) from P1 (18.40 D) to P2 (25.11 D) and to P3 (28.47 D). The large Δµge of P3 leads to efficient exciton dissociation with greatly suppressed charge recombination in P3 ‐based all‐PSCs. Additionally, the fluorination lowers the highest occupied molecular orbital energy level of P3 and P2 , leading to higher open‐circuit voltage (VOC). The power conversion efficiency of the P3 ‐based all‐PSCs (6.42%) outperforms those of the P2 and P1 (5.00% and 2.65%)‐based devices. The reduced charge recombination and the enhanced polymer exciton lifetime in P3 ‐based all‐PSCs are confirmed by the measurements of light‐intensity dependent short‐circuit current density (JSC) and VOC, and time‐resolved photoluminescence. The results provide reciprocal understanding of the charge generation process associated with Δµge in all‐PSCs and suggest an effective strategy for designing π‐conjugated polymers for high performance all‐PSCs.  相似文献   

18.
Two anthracene‐based star‐shaped conjugated small molecules, 5′,5″‐(9,10‐bis((4‐hexylphenyl)ethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), HBantHBT, and 5′,5″‐(9,10‐bis(phenylethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), BantHBT, are used as electron‐cascade donor materials by incorporating them into organic photovoltaic cells prepared using a poly((5,5‐E‐alpha‐((2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,6‐[(1,5‐didecyloxy)naphthalene])) (PBTADN):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) blend. The small molecules penetrate the PBTADN:PC71BM blend layer to yield complementary absorption spectra through appropriate energy level alignment and optimal domain sizes for charge carrier transfer. A high short‐circuit current (JSC) and fill factor (FF) are obtained using solar cells prepared with the ternary blend. The highest photovoltaic performance of the PBTADN: BantHBT :PC71BM blend solar cells is characterized by a JSC of 11.0 mA cm?2, an open circuit voltage (VOC) of 0.91 V, a FF of 56.4%, and a power conversion efficiency (PCE) of 5.6% under AM1.5G illumination (with a high intensity of 100 mW?2). The effects of the small molecules on the ternary blend are investigated by comparison with the traditional poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) system.  相似文献   

19.
Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk‐heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2‐b:2?,3?‐d]pyrrol) core with meta‐ or para‐alkoxyphenyl sidechains are designed and denoted as m‐INPOIC or p‐INPOIC , respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart ( INPIC‐4F ) bearing para‐alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m‐INPOIC presents predominant face‐on orientation to promote charge transport. The as‐cast organic solar cells (OSCs) by blending m‐INPOIC and PBDB‐T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC71BM as the solid processing‐aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as‐cast single‐junction OSCs reported in literature to date. More attractively, PBDB‐T: m‐INPOIC :PC71BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as‐cast devices make m‐INPOIC a promising candidate NFA for large‐scale solution‐processable OSCs.  相似文献   

20.
We report the use of isobenzofulvene–C60 adducts in bulk heterojunction organic solar cells, synthesized via the [4 + 2] cycloaddition of C60 with an in situ generated isobenzofulvene intermediate. The LUMO energy levels of these adducts are 20–180 meV higher than that of PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). This large increase of the LUMO level is attributed to cofacial π-orbital interactions between the fullerene surface and the isobenzofulvene π–system (aromatic ring and double bond). Raised LUMO levels of fullerenes, together with their desirably slow recombination dynamics, led to higher open-circuit voltages (VOC) in bulk heterojunction polymer solar cells (up to 0.75 V for bisadducts) relative to cells tested in parallel using the well-known PCBM as the fullerene acceptor. In addition to enhanced VOC, the short-circuit current densities (JSC) were improved in the devices containing the epoxide analogs of the isobenzofulvene–C60. Notably the epoxide derivative of the monoadduct (IBF–Ep) exhibited ∼20% enhancement of power conversion efficiency (PCE) compared to reference P3HT:PCBM solar cells. A combination of optical and electronic methods was used to investigate the origin of the PCE enhancement observed with these new fullerene acceptors with particular attention to the increased VOCs.  相似文献   

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