High-efficiency Organic Solar Cells Research Articles

Suppressing Static and Dynamic Disorder for High-Efficiency and Stable Thick-Film Organic Solar Cells via Synergistic Dilution Strategy.

Developing stable and highly efficient thick-film organic solar cells (OSCs) is crucial for the large-scale commercial application of organic photovoltaics. A novel synergistic dilution strategy to address this issue, using Polymethyl Methacrylate (PMMA) -modified zinc oxide (ZnO) as the interfacial layer, is introduced. This strategy effectively mitigates oxygen defects in ZnO while also regulating the self-assembly process of the active layer to achieve an ordered distribution of donors and acceptors. In synergistic diluted devices, the dynamic disorder is reduced owing to the suppression of electron-phonon coupling, while the static disorder is suppressed by improved molecular stacking and enhanced intermolecular interactions. Consequently, the 300nm PM6:L8-BO device post-synergistic dilution manifests a marked enhancement in device performance, achieving a photovoltaic power conversion efficiency (PCE) >17% with excellent thermal stability. A typical ternary system is selected to explore the general applicability of synergistic dilution strategy, the PCE has been enhanced significantly from 17.89% to 18.72%, which falls within the range of the highest values among inverted single junction OSCs. As a practical application that depends on the pivotal synergy between high efficiency and stability, this approach paves the way for large-scale implementation of OSCs and ensures cost-effectiveness.

Morphology Optimization by Non-Halogenated and Twisted Volatile Solid Additive for High-Efficiency Organic Solar Cells.

Recently, volatile solid additives have attracted tremendous interest in the field of organic solar cells (OSCs), which can effectively improve device efficiency without sacrificing the reproducibility and stability of the device. However, the structure of reported solid additives is onefold and its working mechanism needs to be further investigated. Herein, a novel non-halogenated and twisted solid additive 1,4-diphenoxybenzene (DPB) is employed to optimize the morphology of the active layer in OSCs. The properties of additive DPB, morphology of active layer, and carrier dynamics behaviors have been systematically investigated through theoretical calculations, in situ and ex situ spectroscopy, grazing-incidence wide-angle X-ray scattering (GIWAXS), and grazing-incidence small-angle X-ray scattering (GISAXS) measurement, as well as ultrafast spectroscopy technology. The results reveal that the twisted additive DPB selectively interacts with acceptor Y6, and thus forms optimized morphology of active layer with increased molecular crystallinity, tight molecular packing, and favorable phase separation. As a result, the optimized devices deliver a remarkable power conversion efficiency (PCE) of 19.04%, which is the highest value for the D18-Cl:N3 system to date. These results demonstrate that non-halogenated and twisted solid additive DPB has broad prospects in the preparation of highly efficient OSCs, providing theoretical and experimental guidance for the development of high-performance solid additives.

Ionized Phenanthroline Derivatives Suppressing Interface Chemical Interactions with Active Layer for High-efficiency Organic Solar Cells with Exceptional Device Stability.

The contact interface between the charge transport interlayer and the active layer is crucial for the non-fullerene organic solar cells (NF OSCs) to achieve high efficiency and long-term stability. In this study, two novel phenanthroline (Phen) derivatives, tbp-Phen and tbp-PhenBr, are developed as efficient cathode interfacial materials (CIMs). The larger steric hindrance substituents and the ionization of nitrogen atoms on the Phen framework jointly enable the tbp-PhenBr CIM with a stable film morphology and immensely suppress the detrimental interface chemical interactions with the NF active layer. Consequently, tbp-PhenBr-based OSC achieves a higher efficiency (PCE=16.34%) than bathocuproine (BCP)-based control device (PCE=13.70%) using PM6:Y6 as the active layer. More importantly, the tbp-PhenBr-based device maintains 80% of its initial efficiency (T80) for 3264 h in dark conditions and 220 h after being heated at 85°C, significantly outperforming the BCP-based device. The tbp-PhenBr CIM also shows broad applicability across various binary and ternary active layer systems, affording a notable PCE of 19.49%. Additionally, the tbp-PhenBr CIM can be processed via a thermal evaporation technique and the prepared devices exhibit high reproducibility. This work provides innovative insights into the molecular design of the CIMs for stable and efficient NF OSCs.

2D g-C3N5 p-Doping of Donor Material for High-Efficiency Organic Solar Cells.

Molecular doping of organic semiconductor is a great strategy for significantly regulating the electronic band structure of organic semiconductor while increasing charge mobility and carrier concentration. Here, a facile strategy is presented by introducing 2D g-C3N5 as a p-dopant into PM6, improving the charge mobility and hole carrier concentration of PM6. Moreover, the electron transfer between PM6 and g-C3N5 can effectively downshift the Fermi energy level and highest occupied molecular orbital (HOMO) energy level of PM6, which leads to the increase the built-in electric field of organic solar cells (OSCs). The addition of g-C3N5 also effectively enhances the crystallization of active layer, thereby improving the stability of OSCs. As a result, a champion bulk-heterojunction (BHJ) and layer-by-layer (LbL) structure OSCs are successfully achieved featuring a high-power conversion efficiency of 18.10%/18.25%, simultaneously having excellent device stability. This work shows that introducing a low concentration dopant into organic donor is an effective method for improving the electrical performance of organic donor and the efficiency of OSCs.

Endgroup engineering of the third component for high-efficiency ternary organic solar cells

In this study, we carefully designed and synthesized three A-D-A type molecules, namely YF-C8-CN, YF-C8-S, and YF-C8-O. These molecules feature a 2,2′-bithiophene core, which bears two 2,4,6-tripropylbenzene steric hindrance groups, as the central electron-donating unit, and utilize rhodanine (Rh), thiazolidinedione, and dicyanoyl-modified benzotriazole (BTA) respectively as the electron acceptor unit (A-unit). We investigated their impact as the third component on the performance of ternary organic solar cells (OSCs). Our studies indicate that YF-C8-S, with rhodanine terminal groups, exhibits complementary absorption characteristics and cascaded energy levels when combined with the host binary system (D18:eC9-4F). Compared to YF-C8-CN and YF-C8-O, ternary OSCs based on YF-C8-S demonstrate significantly higher exciton diffusion and charge transport efficiency, favorably impacting the short-circuit current density (JSC) and fill factor (FF) of the OSCs. Furthermore, devices based on YF-C8-S exhibit reduced non-radiative energy loss, contributing to an enhanced open-circuit voltage (VOC). Consequently, ternary OSCs based on YF-C8-S achieve a remarkable efficiency of 19.12%, positioning it among the highest reported values. This comprehensive research on the third component of the YF-C8 series underscores their significant potential for fabricating high-performance ternary OSCs.

Brominated Perylene Diimides as Cathode Interface Materials for High Efficiency Organic Solar Cells

AbstractThe cathode interface materials (CIMs) are crucial for organic solar cells (OSCs). Herein, excellent CIMs PDINN‐Br and PDINN‐2Br are reported, by bromination of PDINN. Both of them have strong work function (WF) tunability, self‐doping properties, and excellent film‐forming properties. They show higher electron mobility (over 2 × 10−4 cm2 V−1 s−1) and conductivity (≈5 × 10−5 S cm−1) than PDINN. Grazing‐incidence wide‐angle X‐ray scattering measurements (GIWAXS) illustrate that PDINN‐2Br has more ordered arrangement than PDINN and PDINN‐Br. PDINN, PDINN‐Br, and PDINN‐2Br in PM6:Y6‐based OSCs lead to 15.96%, 16.71%, and 17.03% power conversion efficiency (PCE), respectively. The PDINN‐2Br has well performance as well in the PM6:PYIT and D18:L8BO OSCs, PCEs of 18.14% and 18.98% are obtained, respectively, which are higher than PDINN (16.97% and 18.01%).

Magnetic Nanocomposite Modified Hybrid Hole-Transport Layer for Constructing Organic Solar Cells with High Efficiencies.

An interface modification layer holds paramount significance in reducing interface carrier recombination and improving the ohmic contact between the active layer and the electrode in organic solar cells (OSCs). Modifying or doping the widely used hole-transport layer (HTL) PEDOT:PSS to adjust the work function, conductivity, and acidity has become a common strategy for achieving high-performance OSCs. Metal oxides and two-dimensional materials as secondary dopants into PEDOT:PSS, respectively, as well as a replacement of PEDOT:PSS both exhibit immense potential for achieving high-performance OSCs due to their excellent electrical properties. Herein, we report a method utilizing a Fe3O4/GO magnetic nanocomposite as a secondary dopant for PEDOT:PSS to modulate its inherent properties for constructing high-efficiency OSCs. The magnetic nanocomposite hybrid HTL exhibits a suitable optical transmittance and higher work function. Meanwhile, it is found that the addition of Fe3O4/GO magnetic nanoparticles expands the domain of PEDOT and enhances the phase separation between PEDOT and PSS segments, thereby improving the conductivity of PEDOT:PSS. By fine-tuning the doping ratio of a Fe3O4/GO magnetic nanocomposite in PEDOT:PSS, the best power conversion efficiency of OSCs based on PM6:L8-BO was up to 18.91%. The notable enhancement of the device's performance was due to the enhanced hole mobility and the improved charge extraction, further complemented by the decreased likelihood of interface recombination brought about by the hybrid HTL. Compared with PEDOT:PSS-based OSCs, an enhanced stability of the hybrid HTL-based device was also obtained. In addition, the diverse adaptability of the hybrid HTL was demonstrated in enhancing the performance of OSCs that are based on PM6:Y6 and PBDB-T:ITIC. The effectiveness and versatility of a magnetic nanocomposite hybrid HTL present opportunities for achieving high-performance OSCs.

Suppressing non-radiative recombination and tuning morphology via central core asymmetric substitution for efficient organic solar cells

It is necessary and challenging to achieve high-efficiency organic solar cells (OSCs) by suppressing nonradiative energy loss (ΔEnr) and fine-tuning active layer morphology through the delicate active material design. In this study, we design two asymmetric acceptors, a-CH-ThCl and a-CH-Th2Cl, featuring asymmetric conjugated substitutions on central cores via single bond linkages. Single crystals analysis indicate that these two acceptors exhibit intense J-aggregation induced by the asymmetric substitution, which favours for their high photoluminescence quantum yields and contributes to reducing non-radiative recombination. Meanwhile, the two asymmetric acceptors demonstrate enhanced miscibility and optimized morphology with the donor D18. Consequently, the binary device based on D18: a-CH-Th2Cl demonstrates an impressive efficiency of up to 19.10 % with a high open-circuit voltage of 0.935 V, attributed to the remarkably low ΔEnr of 0.179 eV and optimized morphology. These results provide an effective strategy for material design to optimize molecular packing, reduce non-radiative recombination and tune active layer morphology to achieve high-efficiency OSCs.

Frenkel and Charge-Transfer Excitonic Couplings Strengthened by Thiophene-Type Solvent Enables Binary Organic Solar Cells with 19.8 % Efficiency.

Overcoming the trade-off between short-circuited current (Jsc) and open-circuited voltage (Voc) is important to achieving high-efficiency organic solar cells (OSCs). Previous works modulated the energy gap between Frenkel local exciton (LE) and charge-transfer (CT) exciton, which served as the driving force of exciton splitting. Differently, our current work focuses on the modulation of LE-CT excitonic coupling (tLE-CT) via a simple but effective strategy that the 2-chlorothiophene (2Cl-Th) solvent utilizes in the treatment of OSC active-layer films. The results of our experimental measurements and theoretical simulations demonstrated that 2Cl-Th solvent initiates tighter intermolecular interactions with non-fullerene acceptor in comparison with that of traditional chlorobenzene solvent, thus suppressing the acceptor's over-aggregation and retarding the acceptor crystallization with reduced trap. Critically, the resulting shorter distances between donor and acceptor molecules in the 2Cl-Th treated blend efficiently strengthen tLE-CT, which not only promotes exciton splitting but also reduces non-radiative recombination. The champion efficiencies of 19.8 % (small-area) with superior operational reliability (T80: 586 hours) and 17.0 % (large-area) were yielded in 2Cl-Th treated cells. This work provided a new insight into modulating the exciton dynamics to overcome the trade-off between Jsc and Voc, which can productively promote the development of the OSC field.

Interpretable AI and Machine Learning Classification for Identifying High-Efficiency Donor-Acceptor Pairs in Organic Solar Cells.

To enhance the efficiency of organic solar cells, accurately predicting the efficiency of new pairs of donor and acceptor materials is crucial. Presently, most machine learning studies rely on regression models, which often struggle to establish clear rules for distinguishing between high- and low-performing donor-acceptor pairs. This study proposes a novel approach by integrating interpretable AI, specifically using Shapely values, with four supervised machine learning classification models, namely, support vector machines, decision trees, random forest, and gradient boosting. These models aim to identify high-efficiency donor-acceptor pairs based solely on chemical structures and to extract important features that establish general design principles for distinguishing between high- and low-efficiency pairs. For validation purposes, an unsupervised machine learning algorithm utilizing loading vectors obtained from the principal component analysis is employed to identify crucial features associated with high-efficiency donor-acceptor pairs. Interestingly, the features identified by the supervised machine learning approach were found to be a subset of those identified by the unsupervised method. Noteworthy features include the van der Waals surface area, partial equalization of orbital electronegativity, Moreau-Broto autocorrelation, and molecular substructures. Leveraging these features, a backward-working model can be developed, facilitating exploration across a wide array of materials used in organic solar cells. This innovative approach will help navigate the vast chemical compound space of donor and acceptor materials essential in creating high-efficiency organic solar cells.

Highly electronegative additives suppress energetic disorder to realize 19.19 % efficiency binary organic solar cells

Additive engineering plays an important role in realizing high efficiency organic solar cells (OSCs). The introduction or residual of additives usually increases the energetic disorder of the active layer, which in turn causes a significant reduction of the open-circuit voltage (VOC). Herein, this work proposes a novel additive design approach, that is, using the highly electronegative groups trifluoromethyl and trifluoromethoxy to replace one bromine atom of 1,3,5-tribromobenzene (TBB) to obtain 3,5-Dibromobenzotrifluoride (DBTF) and 3,5-Dibromo-triffluoromethoxybenzene (DBOF). This series of additives can induce strong π-π coupling with acceptor, modulating molecular crystallization and orderly stacking, and thus reducing the non-radiative energy loss and energetic disorder of the OSCs. Furthermore, DBTF and DBOF have good volatility and can be removed from the active layer without any post-processing. Consequently, a high power conversion efficiency (PCE) of 18.78 % is obtained in D18: Y6-based OSCs and a remarkable PCE of 19.19 % is realized in D18-Cl/ Y6-based OSCs. Compared with the OSCs without or with conventional TBB additives, the DBOF-treated OSCs effectively suppress the reduction of VOC while enhancing PCE. This work provides guidance for the design and synthesis of additives with selectivity, auto-removability, and the ability to reduce the energetic disorder of the OSCs.

Conjugation-Broken Dimer Acceptors Enable High-Efficiency, Stable, and Flexibility-Robust Organic Solar Cells.

Dimer acceptors in organic solar cells (OSCs) offer distinct advantages, including a well-defined molecular structure and excellent batch-to-batch reproducibility. Their high glass transition temperature (Tg) aids in achieving an optimal kinetic morphology, thereby enhancing device stability. Currently, most of dimer acceptor materials are linked with conjugated units in order to obtain high power conversion efficiencies (PCEs). In this study, different from previous works on conjugation-linked dimer acceptors, a novel series of dimer acceptors are synthesized (named T1, T4, T6, and T12), each linked with different flexible alkyl linkers, and investigated their PCEs, device stability, and flexibility robustness. When blended with PM6, the T6-based device achieves a PCE of 17.09%, comparable to the fully conjugated T0-based device's PCE of 17.12%. The molecular dynamics simulations anddensity functional theorycalculations suggested that flexible conjugation-broken linkers (FCBLs) promote intermolecular electronic couplings, thereby maintaining good electron mobilities of dimer acceptors. Notably, the T6-based device exhibits impressive long-term stability with a T80 lifetime of 1427h, while in the T0-based device, T80 is only 350h. The present work has thus established the relationship between the length of flexible alkyl linkers in such dimer acceptors and the performance and stability of OSCs, which is important to further designing new materials for the fabrication of efficient and stable OSCs.

Asymmetric Alkylthio Branched Chain on Pentacyclic Small Molecular Acceptors Enables High Efficiency Organic Solar Cells

Solution‐processible organic solar cells (OSCs) have gained much attention as one of the most promising options for sustainable energy. With rapidly increasing efficiency of OSCs, developing small molecular acceptors (SMAs) with simple molecular structures are critical for reducing the cost of photovoltaics. Herein, three new SMAs (BZ4F‐C2SEH, BZ4F‐2C2SEH, BZ4F‐SEH) are designed by the incorporation of ethyl(2‐ethylhexyl)sulfane or (2‐ethylhexyl)‐sulfane at the β‐position of thiophene. As a result, the BZ4F‐C2SEH‐based devices obtained an optimal PCE of 15.08% with a good balance between open‐circuit voltage (Voc = 0.87 V) and short‐circuit current density (Jsc = 23.27 mA cm−2) by blending with low‐cost polymer donor PTQ10. Besides, the BZ4F‐C2SEH based devices treated by thermal annealing (TA) and solvent annealing (SVA) deliver a satisfactory power conversion efficiency (PCE) of 16.18% with a Voc of 0.88 V, and a Jsc of 23.98 mA cm−2. This work highlights that attaching asymmetric alkylthio side chain at the β‐position of thiophene can be used as an effective molecular design strategy to trade off Voc and Jsc, thus improving the photovoltaic performance of OSCs.

Synergistically Modulating the Bay and Amid Sites of a Perylene Diimide Cathode Interface Layer for High-Efficiency and High-Stability Organic Solar Cells

Synergistically Modulating the <i>Bay and Amid</i> Sites of a Perylene Diimide Cathode Interface Layer for High-Efficiency and High-Stability Organic Solar Cells

A polymer bilayer hole transporting layer architecture for high-efficiency and stable organic solar cells

A polymer bilayer hole transporting layer architecture for high-efficiency and stable organic solar cells

Efficient and Stable Air-Processed Organic Solar Cells Enabled by an Antioxidant Additive.

Current high-efficiency organic solar cells (OSCs) are generally fabricated in an inert atmosphere that limits their real-world scalable manufacturing, while the efficiencies of air-processed OSCs lag far behind. The impacts of ambient factors on solar cell fabrication remain unclear. In this work, the effects of ambient factors on cell fabrication are systematically investigated, and it is unveiled that the oxidation and doping of organic light absorbers are the dominant reasons causing cell degradation when fabricated in air. To address this issue, a new strategy for fabricating high-performance air-processed OSCs by introducing an antioxidant additive (4-bromophenylhydrazine, BPH) into the precursor solutions, is developed. BPH can effectively inhibit oxygen infiltration from the ambient to the photoactive layer and suppress trap formation caused by oxidation. Compared with conventional air-processed OSCs, this strategy remarkably increases the cell power conversion efficiency (PCE) from 16.7% to 19.3% (independently certified as 19.2%), representing the top value of air-processed OSCs. Furthermore, BPH significantly improves the operational stability of the cells in air by two times with a T80 lifetime of over 500 h. This study highlights the potential of using antioxidant additives to fabricate high-efficiency and stable OSCs in air, significantly promoting the industrialization of OSCs.

Elucidating different roles of solvent additives in organic photovoltaics under solar and indoor light emission environments

Incorporation of solvent additive in bulk heterojunction layer has been effective method for the optimization of film morphology and crystallinity, enabling high efficiency organic solar cells under standard 1 SUN illumination. However, the effects of the additives in low-intensity indoor light environment have not been investigated much so far. In this study, a new donor polymer (PBz-ET) having an efficient spectral matching with LED was synthesized and employed. Moreover, we elucidate the different roles of additives for organic solar cell operations depending on 1 SUN and low-intensity LED illuminations. Through systemic characterizations on morphology, crystallinity, and electrical properties, we found that the additive boosting nanoscale phase separation is compatible for the organic solar cells working in 1 SUN illumination while the additive being capable of increasing crystallinity is more adaptable to those used for indoor light environment. The results in this study suggest a rational selection rule of additives for designing organic solar cells in different light environments.

Deuterated chloroform replaces ultra-dry chloroform to achieve high-efficient organic solar cells

Chloroform is a common and excellent solvent for preparing high-efficient organic solar cells (OSCs), however, it is toxic and poisonable chemical. In comparisons, deuterated chloroform (DC) is less toxic and costly, and particularly, it is non-poisonable chemical. In this paper, we use DC to replace ultra-dry chloroform (UC) as the processing solvent for preparation of active layers of organic solar cells. First, we selected PM6:BTP-eC9 as the basic binary and counted 100 solar cells’ data, from which comparable device performance were obtained with use of DC and UC. Interestingly, DC showed better reproducibility, superior storage under a nitrogen atmosphere and a little better performance than UC. Both DC and UC gave rise of comparable hole and electron mobilities and similar charge recombination losses. Second, we based PM6:Y6 and D18-Cl:Y6 as the binaries and similar effects were obtained from both UC and DC when counting 30 devices for each binary. Third, the universality of the use of DC for preparing high-efficient OSCs were again checked with several binary and ternary systems. In all, this study demonstrate that DC can replace UC for use in the field of OSCs.

Efficiency enhancement of non-fullerene organic solar cells using PEDOT:PSS diluted with alcohol solvents as the hole transport layer

The poly3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) hole transport layer (HTL) has always played a crucial role in achieving high-efficiency organic solar cells (OSCs) owing to its unique advantages of suitable energy levels and high optical transparency. However, the inherent insulation and easy aggregation property of PSS results in relatively low conductivity and high surface roughness of the PEDOT:PSS film, which is unfavorable for charge transport and the morphology of the top layer. To address these problems, we use PEDOT:PSS diluted in a series of alcoholic solvents and evaluate them on the PM6:Y6 system. Among these, the PM6:Y6 devices using PEDOT:PSS modified with ethanol as the HTL demonstrate the best vertical phase segregation and carrier extraction. In addition, the PEDOT:PSS film with added ethanol also has the smoothest surface compared to those diluted in the other alcoholic solvents. Finally, a high power conversion efficiency of 18.13% was obtained with the PM6:Y6 devices based on PEDOT:PSS modified by ethanol. This work provides a sufficient reference for the alcoholic modification of PEDOT:PSS and also proposes a feasible solution for high-efficiency OSCs.

An Asymmetric Coumarin-Anthracene Conjugate as Efficient Fullerene-Free Acceptor for Organic Solar Cells.

Asymmetric wide-band gap fullerene-free acceptors (FFAs) play a crucial role in organic solar cells (OSCs). Here, we designed and synthesized a simple asymmetric coumarin-anthracene conjugate named CA-CN with optical band gap of 2.1 eV in a single-step condensation reaction. Single crystal X-ray structure analysis confirms various multiple intermolecular non-covalent interactions. The molecular orbital energy levels of CA-CN estimated from cyclic voltammetry were found to be suitable for its use as an acceptor for OSCs. Binary OSCs fabricated using CA-CN as acceptor and PTB7-Th as the donor achieve a power conversion efficiency (PCE) of 11.13 %. We further demonstrate that the insertion of 20 wt % of CA-CN as a third component in ternary OSCs with PTB7-Th : DICTF as the host material achieved an impressive PCE of 14.91 %, an improvement of ~43 % compared to the PTB7-Th : DICTF binary device (10.38 %). Importantly, the ternary blend enhances the absorption coverage from 400 to 800 nm and improves the morphology of the active layer. The findings highlight the efficacy of an asymmetric design approach for FFAs, which paves the way for developing high-efficiency OSCs at low cost.