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1.
    
Solution‐processed small molecule (SM) solar cells have the prospect to outperform their polymer‐fullerene counterparts. Considering that both SM donors/acceptors absorb in visible spectral range, higher expected photocurrents should in principle translate into higher power conversion efficiencies (PCEs). However, limited bulk‐heterojunction (BHJ) charge carrier mobility (<10‐4 cm2 V‐1 s‐1) and carrier lifetimes (<1 µs) often impose active layer thickness constraints on BHJ devices (≈100 nm), limiting external quantum efficiencies (EQEs) and photocurrent, and making large‐scale processing techniques particularly challenging. In this report, it is shown that ternary BHJs composed of the SM donor DR3TBDTT (DR3), the SM acceptor ICC6 and the fullerene acceptor PC71BM can be used to achieve SM‐based ternary BHJ solar cells with active layer thicknesses >200 nm and PCEs nearing 11%. The examinations show that these remarkable figures are the result of i) significantly improved electron mobility (8.2 × 10‐4 cm2 V‐1 s‐1), ii) longer carrier lifetimes (2.4 µs), and iii) reduced geminate recombination within BHJ active layers to which PC71BM has been added as ternary component. Optically thick (up to ≈500 nm) devices are shown to maintain PCEs >8%, and optimized DR3:ICC6:PC71BM solar cells demonstrate long‐term shelf stability (dark) for >1000 h, in 55% humidity air environment.  相似文献   

2.
    
The effects of solvent additive (1,8‐diiodooctane (DIO)) on the morphology, charge generation, transport, and recombination in solution‐processed small‐molecule solar cells are studied and these parameters are correlated with device performance. In the optimum nanoscale morphology, which is processed with 0.4% DIO, the phase separation is large enough to create a percolating pathway for carrier transport, yet still small enough to form large interfacial area for efficient charge separation. Complete phase separation in this film reduces the interfacial defects, which occurs without DIO, and hence suppresses the monomolecular recombination. Moreover, balanced charge transport and weak bimolecular recombination lead to a high fill factor (72%). On the other hand, an excess amount of DIO (0.8%) in the solvent results in the over‐aggregation of the donor phase, which disturbs the percolating pathway of the acceptor phase and reduces the electron mobility. The over‐aggregation of the donor phase also shrinks the interfacial area for charge separation and consequently reduces the photocurrent generation.  相似文献   

3.
    
Organic bulk heterojunction solar cells based on small molecule acceptors have recently seen a rapid rise in the power conversion efficiency with values exceeding 13%. This impressive achievement has been obtained by simultaneous reduction of voltage and charge recombination losses within this class of materials as compared to fullerene‐based solar cells. In this contribution, the authors review the current understanding of the relevant photophysical processes in highly efficient nonfullerene acceptor (NFA) small molecules. Charge generation, recombination, and charge transport is discussed in comparison to fullerene‐based composites. Finally, the authors review the superior light and thermal stability of nonfullerene small molecule acceptor based solar cells, and highlight the importance of NFA‐based composites that enable devices without early performance loss, thus resembling so‐called burn‐in free devices.  相似文献   

4.
    
Symmetry breaking provides a new material design strategy for nonfullerene small molecule acceptors (SMAs). The past 10 years have witnessed significant advances in asymmetric nonfullerene SMAs in organic solar cells (OSCs) with power conversion efficiency (PCE) increasing from ≈1% to ≈14%. In this review, the progress of asymmetric nonfullerene SMAs, including early reports of asymmetric nonfullerene SMAs, asymmetric PDI‐based nonfullerene SMAs, and asymmetric acceptor–donor–acceptor (A–D–A)‐type nonfullerene SMAs, is summarized. The structure–property relationships and the perspectives for future development of asymmetric nonfullerene SMAs are also discussed.  相似文献   

5.
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6.
    
All‐inorganic CsPbIBr2 perovskite solar cells (pero‐SCs) exhibit excellent overall stability, but their power conversion efficiencies (PCEs) are greatly limited by their wide bandgaps. Integrated solar cells (ISCs) are considered to be an emergent technology that could extend their photoresponse by directly stacking two distinct photoactive layers with complementary bandgaps. However, rising photocurrents always sacrifice other photovoltaic parameters, thereby leading to an unsatisfactory PCE. Here, a recast strategy is proposed to optimize the spatial distribution components of low‐bandgap organic bulk‐heterojunction (BHJ) film, and is combined with an all‐inorganic perovskite to construct perovskite/BHJ ISCs. With this strategy, the integrated perovskite/BHJ film with a top‐enriched donor‐material spatial distribution is shown to effectively improve ambipolar charge transport behavior and suppress charge carrier recombination. For the first time, the ISC is not only significantly extended and enhanced the photoresponse achieving a 20% increase in current density, but also exhibits a high open‐circuit voltage and fill factor at the same time. As a result, a record PCE of 11.08% based on CsPbIBr2 pero‐SCs is realized; it simultaneously shows excellent long‐term stability against heat and ultraviolet light.  相似文献   

7.
    
In this study, a comprehensive analytical model to quantify the total nongeminate recombination losses, originating from bimolecular as well as bulk and surface trap‐assisted recombination mechanisms in nonfullerene‐based bulk heterojunction organic solar cells is developed. This proposed model is successfully employed to obtain the different contributions to the recombination current of the investigated solar cells under different illumination intensities. Additionally, the model quantitatively describes the experimentally measured open‐circuit voltage versus light intensity dependence. Most importantly, it is possible to calculate the experimental results with the same fitting parameter values from the presented model. The validity of this model is also proven by a combination of other independent, steady‐state, and transient experimental techniques. This new powerful analytical tool will enable researchers in the photovoltaic community to take into account the synergetic contribution from all relevant types of nongeminate recombination losses in different optoelectronic systems and target their analysis of recombination dynamics at any operating voltage.  相似文献   

8.
    
Reducing energy loss (Eloss) is of critical importance to improving the photovoltaic performance of organic solar cells (OSCs). Although nonradiative recombination ( E loss nonrad ) is investigated in quite a few works, the method for modulating E loss nonrad is seldom reported. Here, a new method of depressing Eloss is reported for nonfullerene OSCs. In addition to ternary‐blend bulk heterojunction (BHJ) solar cells, it is proved that a small molecular material (NRM‐1) can be selectively dispersed into the acceptor phase in the PBDB‐T:IT‐4F‐based OSC, resulting in lower E loss rad and E loss nonrad , and hence a significant improvement in the open‐circuit voltage (VOC); under an optimal feed ratio of NRM‐1, an enhanced power conversion efficiency can also be gained. Moreover, the role of NRM‐1 in the method is illustrated and its applicability for several other representative OSCs is validated. This work paves a new pathway to reduce the Eloss for nonfullerene OSCs.  相似文献   

9.
    
Understanding the correlation between polymer aggregation, miscibility, and device performance is important to establish a set of chemistry design rules for donor polymers with nonfullerene acceptors (NFAs). Employing a donor polymer with strong temperature‐dependent aggregation, namely PffBT4T‐2OD [poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3″′‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2″′‐quaterthiophen‐5,5‐diyl)], also known as PCE‐11 as a base polymer, five copolymer derivatives having a different thiophene linker composition are blended with the common NFA O‐IDTBR to investigate their photovoltaic performance. While the donor polymers have similar optoelectronic properties, it is found that the device power conversion efficiency changes drastically from 1.8% to 8.7% as a function of thiophene content in the donor polymer. Results of structural characterization show that polymer aggregation and miscibility with O‐IDTBR are a strong function of the chemical composition, leading to different donor–acceptor blend morphology. Polymers having a strong tendency to aggregate are found to undergo fast aggregation prior to liquid–liquid phase separation and have a higher miscibility with NFA. These properties result in smaller mixed donor–acceptor domains, stronger PL quenching, and more efficient exciton dissociation in the resulting cells. This work indicates the importance of both polymer aggregation and donor–acceptor interaction on the formation of bulk heterojunctions in polymer:NFA blends.  相似文献   

10.
    
Here, it is investigated whether an energetic cascade between mixed and pure regions assists in suppressing recombination losses in non‐fullerene acceptor (NFA)‐based organic solar cells. The impact of polymer‐NFA blend composition upon morphology, energetics, charge carrier recombination kinetics, and photocurrent properties are studied. By changing film composition, morphological structures are varied from consisting of highly intermixed polymer‐NFA phases to consisting of both intermixed and pure phase. Cyclic voltammetry is employed to investigate the impact of blend morphology upon NFA lowest unoccupied molecular orbital (LUMO) level energetics. Transient absorption spectroscopy reveals the importance of an energetic cascade between mixed and pure phases in the electron–hole dynamics in order to well separate spatially localized electron–hole pairs. Raman spectroscopy is used to investigate the origin of energetic shift of NFA LUMO levels. It appears that the increase in NFA electron affinity in pure phases relative to mixed phases is correlated with a transition from a relatively planar backbone structure of NFA in pure, aggregated phases, to a more twisted structure in molecularly mixed phases. The studies focus on addressing whether aggregation‐dependent acceptor LUMO level energetics are a general design requirement for both fullerene and NFAs, and quantifying the magnitude, origin, and impact of such energetic shifts upon device performance.  相似文献   

11.
    
A terthieno[3,2‐b]thiophene ( 6T ) based fused‐ring low bandgap electron acceptor, 6TIC , is designed and synthesized for highly efficient nonfullerene solar cells. The chemical, optical, and physical properties, device characteristics, and film morphology of 6TIC are intensively studied. 6TIC shows a narrow bandgap with band edge reaching 905 nm due to the electron‐rich π‐conjugated 6T core and reduced resonance stabilization energy. The rigid, π‐conjugated 6T also offers lower reorganization energy to facilitate very low VOC loss in the 6TIC system. The analysis of film morphology shows that PTB7‐Th and 6TIC can form crystalline domains and a bicontinuous network. These domains are enlarged when thermal annealing is applied. Consequently, the device based on PTB7‐Th : 6TIC exhibits a high power conversion efficiency (PCE) of 11.07% with a high JSC > 20 mA cm?2 and a high VOC of 0.83 V with a relatively low VOC loss (≈0.55 V). Moreover, a semitransparent solar cell based on PTB7‐Th : 6TIC exhibits a relatively high PCE (7.62%). The device can have combined high PCE and high JSC is quite rare for organic solar cells.  相似文献   

12.
    
Three acceptor–donor–acceptor type nonfullerene acceptors (NFAs), namely, F–F, F–Cl, and F–Br, are designed and synthesized through a halogenation strategy on one successful nonfullerene acceptor FDICTF (F–H). The three molecules show red‐shifted absorptions, increased crystallinities, and higher charge mobilities compared with the F–H. After blending with donor polymer PBDB‐T, the F–F‐, F–Cl‐, and F–Br‐based devices exhibit power conversion efficiencies (PCEs) of 10.85%, 11.47%, and 12.05%, respectively, which are higher than that of F–H with PCE of 9.59%. These results indicate that manipulating the absorption range, crystallinity and mobilities of NFAs by introducing different halogen atoms is an effective way to achieve high photovoltaic performance, which will offer valuable insight for the designing of high‐efficiency organic solar cells.  相似文献   

13.
    
One of the most important factors that limits the efficiencies of bulk‐heterojunction organic solar cells (OSCs) is the modest open‐circuit voltage (Voc) due to their large voltage loss (Vloss) caused by significant nonradiative recombination loss. To boost the performance of OSCs toward their theoretical limit, developing high‐performance donor: acceptor systems featuring low Vloss with suppressed nonradiative recombination losses (<0.30 V) is desired. Herein, high performance OSCs based on a polymer donor benzodithiophene‐difluorobenzoxadiazole‐2‐decyltetradecyl (BDT‐ffBX‐DT) and perylenediimide‐based acceptors (PDI dimer with spirofluorene linker (SFPDI), PDI4, and PDI6) are reported which offer a high power conversion efficiency (PCE) of 7.5%, 56% external quantum efficiency associated with very high Voc (>1.10 V) and low Vloss (<0.60 V). A high Voc up to 1.23 V is achieved, which is among the highest values reported for OSCs with a PCE beyond 6%, to date. These attractive results are benefit from the suppressed nonradiative recombination voltage loss, which is as low as 0.20 V. This value is the lowest value for OSCs so far and is comparable to high performance crystalline silicon and perovskite solar cells. These results show that OSCs have the potential to achieve comparable Voc and voltage loss as inorganic photovoltaic technologies.  相似文献   

14.
    
We report on the effects of screening of the electric field by doping‐induced mobile charges on photocurrent collection in operational organic solar cells. Charge transport and recombination were studied using double injection (DI) and charge extraction by linearly increasing voltage (CELIV) transient techniques in bulk‐heterojunction solar cells made from acceptor‐donor blends of poly(3‐n‐hexylthiophene):phenyl‐C61‐butyric acid methyl ester (P3HT:PC60BM). It is shown that the screening of the built‐in field in operational solar cells can be controlled by an external voltage while the influence on charge transport and recombination is measured. An analytical theory to extract the bimolecular recombination coefficient as a function of electric field from the injection current is also reported. The results demonstrate that the suppressed (non‐Langevin) bimolecular recombination rate and charge collection are not strongly affected by native doping levels in this materials combination. Hence, it is not necessary to reduce the level of doping further to improve the device performance of P3HT‐based solar cells.  相似文献   

15.
    
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16.
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17.
    
A series of narrow bandgap electron acceptors is designed and synthesized for efficient near‐infrared (NIR) organic solar cells. Extending π‐conjugation of donor frameworks leads to an intense intramolecular charge transfer, resulting in broad absorption profiles with band edge reaching 950 nm. When blended with an electron donor polymer PTB7‐Th, IOTIC‐2F exhibits efficient charge transfer even with a small energetic offset, so as to achieve a large photogenerated current over 22 mA cm?2 with small energy losses (≈0.49 eV) in solar cell devices. With an intense NIR absorbance, PTB7‐Th:IOTIC‐2F‐based cells achieve a power conversion efficiency of 12.1% with good visible transparency (52% transmittance from 370 to 740 nm). Analysis of film morphology reveals that processing with solvent additives enhances crystalline features of acceptor components, while keeping an appropriate level of donor:acceptor intermixing in the binary blends. The incorporation of the third component, ITIC‐2F, into the PTB7‐Th:IOTIC‐2F blends increases the device efficiency up to 12.9%. The improvement is assigned to the cascaded energy‐level structure and desirable nanoscale phase separation of the ternary blends, which is beneficial to the photocurrent generation. This work provides an efficient molecular design strategy to optimize nonfullerene acceptor properties for efficient NIR organic photovoltaics.  相似文献   

18.
    
Developing efficient organic solar cells (OSCs) with relatively thick active layer compatible with the roll to roll large area printing process is an inevitable requirement for the commercialization of this field. However, typical laboratory OSCs generally exhibit active layers with optimized thickness around 100 nm and very low thickness tolerance, which cannot be suitable for roll to roll process. In this work, high performance of thick‐film organic solar cells employing a nonfullerene acceptor F–2Cl and a polymer donor PM6 is demonstrated. High power conversion efficiencies (PCEs) of 13.80% in the inverted structure device and 12.83% in the conventional structure device are achieved under optimized conditions. PCE of 9.03% is obtained for the inverted device with active layer thickness of 500 nm. It is worth noting that the conventional structure device still maintains the PCE of over 10% when the film thickness of the active layer is 600 nm, which is the highest value for the NF‐OSCs with such a large active layer thickness. It is found that the performance difference between the thick active layer films based conventional and inverted devices is attributed to their different vertical phase separation in the active layers.  相似文献   

19.
    
The introduction of rigid and extended ladder‐type fused‐ring cores, such as indacenodithiophene, has enabled the synthesis of a variety of nonfullerene small molecules for use as electron acceptors in high‐performance organic photovoltaic cells. Contrasting with recent trends, a very simple‐structured nonfullerene acceptor (NFA), T2‐ORH , consisting of a bithiophene core and octyl‐substituted rhodanine ends, is synthesized in two steps from inexpensive commercially available raw materials. Its relatively short π‐conjugation results in a wide bandgap and a blue‐shifted UV–vis absorption profile complementary to those of poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐co‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th). Despite a sufficient offset between T2‐ORH and PTB7‐Th, the lowest unoccupied molecular orbital (LUMO) energy level of T2‐ORH is still higher than the LUMOs of other NFAs (e.g., ITIC). Therefore, the PTB7‐Th: T2‐ORH blend film exhibits an efficiency of 9.33% with a high open‐circuit voltage of 1.07 V and a short‐circuit current of 14.72 mA cm?2 in an additive‐free single‐junction cell. Importantly, the optimized device displays a remarkably low energy loss of 0.51 eV, in which bimolecular and monomolecular charge recombination is effectively suppressed by solvent vapor annealing treatment. The blend film has a very smooth and homogeneous morphology, providing both vertical and parallel charge transport in the devices.  相似文献   

20.
    
Nonfullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. However, there is very little investigation into the molecular processes of degradation, which is critical to guiding design of novel NFAs for long‐lived, commercially viable OPVs. Here, the important role of molecular structure and conformation in NFA photostability in air is investigated by comparing structurally similar but conformationally different promising NFAs: planar O‐IDTBR and nonplanar O‐IDFBR. A three‐phase degradation process is identified: i) initial photoinduced conformational change (i.e., torsion about the core–benzothiadiazole dihedral), induced by noncovalent interactions with environmental molecules, ii) followed by photo‐oxidation and fragmentation, leading to chromophore bleaching and degradation product formation, and iii) finally complete chromophore bleaching. Initial conformational change is a critical prerequisite for further degradation, providing fundamental understanding of the relative stability of IDTBR and IDFBR, where the already twisted IDFBR is more prone to degradation. When blended with the donor polymer poly(3‐hexylthiophene), both NFAs exhibit improved photostability while the photostability of the polymer itself is significantly reduced by the more miscible twisted NFA. The findings elucidate the important role of NFA molecular structure in photostability of OPV systems, and provide vital insights into molecular design rules for intrinsically photostable NFAs.  相似文献   

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