Application In Organic Solar Cells Research Articles

Fully Non-Fused Ring Electron Acceptors Enable Effective Additive-Free Organic Solar Cells with Enhanced Exciton Diffusion Length.

Low-cost photovoltaic materials and additive-free, non-halogenated solvent processing of photoactive layers are crucial for the large-scale commercial application of organic solar cells (OSCs). However, high-efficiency OSCs that possess all these advantages remain scarce due to the lack of insight into the structure-property relationship. In this work, three fully non-fused ring electron acceptors (NFREAs), DTB21, DTB22, and DTB23, are reported by utilizing a simplified 1,4-di(thiophen-2-yl)benzene (DTB) core with varied alkoxy chain lengths on the thiophene bridge. The material-only costs of these acceptors are only 11-13$ per gram. Importantly, DTB22 has an exciton diffusion length (LD) of up to 25.5nm. The DTB21 and DTB23 exhibit decreased LDs of 20.1 and 23.1nm, respectively. After blending with the polymer donor PBQx-TF, the PBQx-TF:DTB22 film exhibits the fastest hole transfer and the longest carrier recombination lifetime among these OSCs. Consequently, the optimal PBQx-TF:DTB22-based OSC achieves an excellent PCE of 17.00%, which is among the highest values for fully NFREAs. In contrast, the PBQx-TF:DTB21- and PBQx-TF:DTB23-based OSCs show relatively lower PCEs of 15.13% and 15.63%, respectively. Notably, all these OSCs are fabricated using toluene as the solvent, without any additives. Additionally, the DTB22-based OSC also demonstrates good stability, retaining 95% of its initial efficiency after 500 h without encapsulation in a glovebox.

Regulating Intermolecular Interactions and Film Formation Kinetics for Record Efficiency in Difluorobenzothiadizole‐Based Organic Solar Cells

AbstractThe difluorobenzothiadizole (ffBT) unit is one of the most classic electron‐accepting building blocks used to construct D‐A copolymers for applications in organic solar cells (OSCs). Historically, ffBT‐based polymers have achieved record power conversion efficiencies (PCEs) in fullerene‐based OSCs owing to their strong temperature‐dependent aggregation (TDA) characteristics. However, their excessive miscibility and rapid aggregation kinetics during film formation have hindered their performance with state‐of‐the‐art non‐fullerene acceptors (NFAs). Herein, we synthesized two ffBT‐based copolymers, PffBT‐2T and PffBT‐4T, incorporating different π‐bridges to modulate intermolecular interactions and aggregation tendencies. Experimental and theoretical studies revealed that PffBT‐4T exhibits reduced electrostatic potential differences and miscibility with L8‐BO compared to PffBT‐2T. This facilitates improved phase separation in the active layer, leading to enhanced molecular packing and optimized morphology. Moreover, PffBT‐4T demonstrated a prolonged nucleation and crystal growth process, leading to enhanced molecular packing and optimized morphology. Consequently, PffBT‐4T‐based devices achieved a remarkable PCE of 17.5 %, setting a new record for ffBT‐based photovoltaic polymers. Our findings underscore the importance of conjugate backbone modulation in controlling aggregation behavior and film formation kinetics, providing valuable insights for the design of high‐performance polymer donors in organic photovoltaics.

A leap forward in the optimization of organic solar cells: DFT-based insights into the design of NDI-based donor-acceptor-donor structures

This study presents the design and analysis of four novel small molecules with a donor-acceptor-donor (D-A-D) architecture, incorporating naphthalene diimide (NDI) as the central electron acceptor core, flanked by different electron-donating units: 4H-dithieno [3,2-b:2′,3′-d]pyrrole (DTP), isomeric 7H-dithieno-[2,3-b:3′,2′-d]pyrrole (iso-DTP), phenothiazine, and diphenylamine. The optical, electronic, and photovoltaic properties of these structures were evaluated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at the WB97XD/6-311+G (d,p) theoretical level. The selected calculation method showed excellent agreement with experimental data for the synthesized NDI-C3 molecule, validating the computational approach. Our findings highlight the significant role of electron-donating groups in enhancing photovoltaic properties, including increased open-circuit voltage, improved charge density distribution, and enhanced parameters such as fill factor, radiation lifetime, and light harvesting efficiency compared to the NDI-C3 structure. These promising results underscore the potential of our designed molecules for efficient application in organic solar cells and their significant contribution to the advancement of photovoltaic technology.

Design, Synthesis, and Theoretical Studies on the Benzoxadiazole and Thienopyrrole Containing Conjugated Random Copolymers for Organic Solar Cell Applications

Design, Synthesis, and Theoretical Studies on the Benzoxadiazole and Thienopyrrole Containing Conjugated Random Copolymers for Organic Solar Cell Applications

Optimizing non-fullerene acceptor molecules constituting fluorene core for enhanced performance in organic solar cells: a theoretical methodology.

Looking for novel outstanding performance materials suitable for organic solar cells, we constructed a range of non-fullerene acceptors (NFAs) evolved from the recently synthesized acceptor molecule identified as DICTIF, structured around fluorene core where 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene) propanedinitrile presented the terminals end-groups. Employing density functional theory (DFT) and time dependent-DFT (TD-DFT) simulations, we have simulated the impact of altering the end groups of DICTIF molecule by five assorted acceptors molecules, for the purpose of exploring their opto-electronic properties and their performance in organic solar cell (OSC) applications. We proved that the designed non-fullerene acceptors provide enhanced efficiency compared to the synthesized molecule, such as planar geometries and narrower energy gap ranging from 1.51 to 1.95 eV. A red shift in absorption was observed for all tailored molecules (λmax = 583.5-711.4 nm) as compared to the reference molecule (λmax = 578 nm).Various decisive factors such as frontier molecular orbitals (FMOs), exciton binding energy (EB), absorption maximum (λmax), open circuit voltage (VOC), reorganization energies (RE), transition density matrix (TDM), reduced density gradient (RDG), and electron-hole overlap have also been computed for analyzing the performance of NFAs. Low reorganizational energy values facilitate charge mobility which improves the conductivity of all the designed molecules. This study showed that our novel tailored molecules might be suitable candidates for the fabrication of highly efficient photovoltaic materials. After testing various hybrid functionals, optimized geometries were assigned using DFT HSEH1PBE/6-31G(d) level of theory. Electronic excitations and absorption spectra were investigated using the TD-DFT MPW1PW91/6-31G(d) level of theory. We ascertained that HSEH1PBE/6-31G(d) level of theory yield the closest calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the DICTIF to the corresponding experimental ones and that TD-MPW1PW91//6-31G(d) was the most suitable level of theory for exploring electronic excitations and finding the maximum of absorption (λmax).

Linkage Regulation of Back‐To‐Back Connected Dimers as Guest Acceptors Enables Organic Solar Cells with Excellent Efficiency, Stability and Flexibility

AbstractHigh efficiency, stability, and flexibility are key prerequisites for the commercial applications of organic solar cells (OSCs). Herein, three back‐to‐back connected dimers (2Qx‐TT, 2Qx‐C3, 2Qx‐C6) are developed as the guest acceptors for OSCs with improved comprehensive performance. By regulating the linkage from rigid bithiophene to flexible alkyl chain, the back‐to‐back connected dimers display quite different molecular geometry and intermolecular interactions, consequently influencing their packing arrangement, film‐forming process, carrier mobilities, and the device efficiency, stability, and flexibility. By introducing these dimer acceptors as the guest into active layer, these dimers form alloy phases with the host acceptor, promoting film‐forming process and charge dynamics. All ternary devices exhibit improved PCEs of over 18% than the control binary device. Among them, 2Qx‐C3‐based ternary device obtains the best efficiency of as high as 19.03%. Moreover, thanks to the stronger entanglement favored by the dimers with flexible linkage, the PM6:BTP‐eC9:2Qx‐C3‐based device shows outstanding stability and flexibility. The flexible device displays an improved PCE of 16.09% with a crack‐onset strain of 15.0%, showing excellent mechanical robustness close to the all‐polymer devices. This work demonstrates the potential of the back‐to‐back connected dimer acceptors as the guest for highly efficient, stable and flexible OSCs.

Regulating Intermolecular Interactions and Film Formation Kinetics for Record Efficiency in Difluorobenzothiadizole-based Organic Solar Cells.

The difluorobenzothiadizole (ffBT) unit is one of the most classic electron-accepting building blocks used to construct D-A copolymers for applications in organic solar cells (OSCs). Historically, ffBT-based polymers have achieved record power conversion efficiencies (PCEs) in fullerene-based OSCs owing to their strong temperature-dependent aggregation (TDA) characteristics. However, their excessive miscibility and rapid aggregation kinetics during film formation have hindered their performance with state-of-the-art non-fullerene acceptors (NFAs). Herein, we synthesized two ffBT-based copolymers, PffBT-2T and PffBT-4T, incorporating different π-bridges to modulate intermolecular interactions and aggregation tendencies. Experimental and theoretical studies revealed that PffBT-4T exhibits reduced electrostatic potential differences and miscibility with L8-BO compared to PffBT-2T. This facilitates improved phase separation in the active layer, leading to enhanced molecular packing and optimized morphology. Moreover, PffBT-4T demonstrated a prolonged nucleation and crystal growth process, leading to enhanced molecular packing and optimized morphology. Consequently, PffBT-4T-based devices achieved a remarkable PCE of 17.5%, setting a new record for ffBT-based photovoltaic polymers. Our findings underscore the importance of conjugate backbone modulation in controlling aggregation behavior and film formation kinetics, providing valuable insights for the design of high-performance polymer donors in organic photovoltaics.

Solvent‐Induced Copper Vacancy in CuSCN Layer: A Strategy to Boost Conductivity and Optimize Energy Levels for Efficient Organic Solar Cells

AbstractCopper(I) thiocyanate (CuSCN) is a prominent wide‐bandgap p‐type semiconductor with desirable transparency and chemical robustness. Whereas intrinsic limitations, such as its relatively low Fermi level (EF) and modest electrical conductivity, have impeded its broader application in organic solar cells (OSCs). This study introduces a novel approach to modify the electronic properties of CuSCN by inducing copper vacancies through the use of specific solvent mixtures, thereby enhancing its suitability for OSCs. The effects of two solvent mixtures, methanol/ammonia (CH3OH/NH4OH) and dimethyl sulfoxide/N,N‐Dimethylformamide (DMSO/DMF) is have systematically investigated, on the CuSCN layer. The findings reveal that these solvent systems induce a higher concentration of copper vacancies within the CuSCN film, resulting in a significant reduction of the EF and a substantial increase in electrical conductivity. These modifications have led to the improved energy level alignment with the PM6:L8‐BO:BTP‐eC9 blended photoactive layers, culminating in a marked enhancement of the power‐conversion efficiencies of 19.10% for the DMSO/DMF processed CuSCN layer. Additionally, it has observed enhanced shelf/thermal stability and thickness tolerance of OSCs based on these CuSCN films. This work not only presents a novel strategy for modifying the performance characteristics of CuSCN but also underscores its potential to contribute to the advancement of photovoltaic technologies.

Preparation and performance study of organic small molecule photovoltaic donor materials in solar cells

Abstract In this study, PDPAT-BDT-BT was used as a donor material, combined with PC61BM and PC71BM as acceptor materials, to prepare a hybrid thin film for organic solar cells. In photovoltaic performance tests, this film shows advantages and good characteristics. The experimental results show that the PDPAT-BDT-BT polymer shows good performance in terms of thermal stability, optical properties, and electrochemical properties. It also shows better photovoltaic performance in the hybrid system with PC71BM, which lays a good foundation for its potential application in organic solar cells.

Exploration of the effect of multiple acceptor and π–spacer moieties coupled to indolonaphthyridine core for promising organic photovoltaic properties: a first principles framework

Herein, the indolonaphthyridine-based molecules (INDTD1–INDTD8) with A1–π–A2–π–A1 configuration were designed by the end-capped modification of INDTR reference with various acceptors. The density functional theory (DFT) and time-dependent DFT (TD-DFT) analyses at M06/6-31G(d,p) level were reported in this research to explore their optoelectronic and photovoltaic features. Their geometrical structures were initially optimized at the afore-said level and followed by various calculations such as the frontier molecular orbitals (FMOs), UV–Visible, density of states (DOS), transition density matrix (TDM), binding energy (Eb), open circuit voltage (Voc) and fill factor (FF). Moreover, their global reactivity parameters (GRPs) were depicted by using the HOMO–LUMO band gaps obtained from the FMOs study. The tailored molecules demonstrated lower band gaps (2.183–2.269 eV) than INDTR (2.288 eV). They also showed bathochromic shifts in the visible region in chloroform (735.937–762.318 nm) and gas phase (710.384–729.571 nm) as compared to INDTR (724.710 and 698.498 nm, respectively). Further, intramolecular charge transfer (ICT) was demonstrated via the DOS and TDM graphical maps. Among all the entitled chromophores, INDTD7 showed significantly reduced band gap (2.183 eV), red-shifted absorption value (760.914 nm) in chloroform solvent and minimal Eb value (0.554 eV). The presence of –SO3H groups on the terminal acceptors of INDTD7 may enhance the mobility of charges. The results suggested that the newly designed chromophores can be effective candidates for the future organic solar cell applications. Moreover, this study may encourage the experimentalists to develop photovoltaic materials.

Thiophene Oligomers with Low Cost and Easy Synthesis for Efficient Organic Solar Cells

Hole‐transporting layer (HTL) materials with sufficient hole collection ability, noncorrosive nature, and easy preparation are strongly desired for the field of organic solar cells (OSCs). The development of new materials and synthetic methods has been proved to be the essential approach to improve the HTL performances. Herein, a series of thiophene oligomers TO‐P1, TO‐P2, and TO‐P3 are designed and synthesized through coupling reaction by using the polyoxometalates as the oxidizing reagents. The thiophene oligomers can be readily synthesized under ambient condition with high yield. Among the as‐prepared thiophene oligomers, TO‐P2 exhibits neutral pH, sufficient work function, and high conductivity, endowing the HTL with excellent hole collection ability. Also, TO‐P2 possesses good chemical stability and satisfied solution processability, which is important for practical use. By using TO‐P2 as HTL, OSC shows a photovoltaic efficiency of 17.25%. Furthermore, TO‐P2 is a universal HTL that can be used to fabricate efficient OSCs with various active layers. More importantly, TO‐P2 shows good compatibility with large‐area processing technique. A 1 cm2 OSC is fabricated by using a blade‐coated TO‐P2 HTL, exhibiting a power conversion efficiency of 15.0%. The easy preparation and noncorrosive nature endow TO‐P2 with great potential application in OSCs.

Non-fused ring electron acceptor based on phenyl-substituted benzodithiophenedione unit via chlorinated terminal groups for constructing efficient organic solar cells

Non-fused ring electron acceptors (NFREAs) have displayed promising candidates for practical application of organic solar cells (OSCs) owing to their short synthesis routes and cost effectiveness. The terminal groups halogenation have facilitated the optimization the physicochemical properties of NFREAs. In this work, we developed two NFREAs using a phenyl-substituted benzodithiophenedione unit as central core and electron-withdrawing groups 2-(3-oxo-2,3-dihydro-1 H-inden-1-ylidene) malononitrile (IC) or chlorinated IC (IC-2Cl) as the terminal groups. These NFREAs were designated as BDDPh-H and BDDPh-Cl, respectively. DFT calculations revealing that both NFREAs exhibited good backbone coplanarity due to S…O noncovalent interactions, and BDDPh-Cl exhibited red-shifted absorption compared with BDDPh-H owing to the stronger molecular stacking caused by chlorinated terminal groups. Moreover, BDDPh-Cl-based blended film demonstrated better nano-scale morphology, facilitating exciton dissociation and charge transport. Thus, PM6: BDDPh-Cl-based OSCs achieved a higher power conversion efficiency (PCE) of 12.69 %, outperforming BDDPh-H-based device (3.20 %) due to the enhanced short-circuit current and fill factor. Our findings indicate that combining phenyl-substituted benzodithiophenedione as central unit with chlorinated terminal groups showed great potential to construct highly efficient NFREAs.

Direct C–H Arylation-Derived Oligomeric Building Blocks Incorporated into Conjugated Polymers for Organic Solar Cell Applications

Direct C–H Arylation-Derived Oligomeric Building Blocks Incorporated into Conjugated Polymers for Organic Solar Cell Applications

Effect of Film Thickness on the Electrical Resistivity and Optical Functions Distribution of Iron Tris(8-hydroxyquinoline) Thin Films

Iron tris(8-hydroxyquinoline) (Feq3) was synthesized and investigated by X-ray photoemission spectroscopy. It crystalizes in triclinic polycrystalline structure in powder form, whereas the Feq3 films, with different thickness values (12, 20, 35, and 42 nm), have an amorphous structure. The influence of film thickness on the electrical resistivity and the optical properties is reported. The morphology of Feq3 was investigated in terms of field-emission scanning electron microscope. Electrical resistivity measurements indicate an inverse proportionality to the film thickness. The optical properties of Feq3 films were investigated in terms of photoluminescence spectra and spectrophotometric measurements of transmittance and reflectance. The optical functions such as absorption coefficient and refractive index of the films were calculated. The dependence of the Feq3 film thickness on the optical energy band gap and dispersion parameters was studied. The outcomes indicate that the Feq3 films are of great importance for applications in organic solar cells and light emitting diodes.

Organic solar cells: Exploring the future and sustainability of clean energy

As a critical technology in renewable energy, organic solar cells play an important role in energy transition and sustainable development. This paper examines the development and significance of organic solar cells in terms of energy demand, environmental requirements, and industrial growth. With the development of China's energy structure adjustment and carbon peak carbon neutral targets, interest in novel energy technologies is growing. The paper then describes the interaction between photons and materials and the electron-hole separation and charge transport mechanism of organic solar cells. In addition, the characteristics and potential applications of organic solar cells with various structures, such as bilayer heterojunction devices, intrinsic heterojunction devices, molecular DA junction devices, and stacked devices, are described in depth. In the outlook section, the paper emphasizes the future potential of organic solar cells, including efficiency enhancements, cost reductions, and integration with energy storage technologies. In conclusion, organic solar cells have tremendous potential in the field of renewable energy, and they are anticipated to lead the energy transition and contribute to sustainable development.

Transfer Printing of Photoactive Layer Enabling Efficient, Wearable, and Dual‐Function Organic Solar Cell Modules for a Wireless Healthcare Monitoring System

AbstractWhile transfer‐printing is a great technique for efficient film fabrication of many emerging devices on various substrates, its application in organic solar cells (OSCs) is rarely explored. Besides, it is highly challenging to fabricate a large‐scale production of a “dual‐function OSC module” that runs two‐objective functions simultaneously in a given single system. Through comprehensive investigation on the transfer‐printing feasibility of various π‐conjugated organic materials, in addition to successful transfer‐printed OSC and flexible OSC module, implementation of dual‐function OSC modules via the transfer‐printing, in which two individual sub‐cell series based on dual‐purpose photoactive layers are separately integrated into a single system is showcased here. Moreover, the fabrication and operation of a wearable integrated self‐powered system for wireless healthcare monitoring with the wearable transfer‐printed dual‐function OSC module are also demonstrated. This study opens the door to fabricating OSCs with multi‐objective structures via the transfer‐printing technique, which enables the extra device‐level values for advanced energy‐related applications.

Design, Synthesis, and Theoretical Studies on the Benzoxadiazole and Thienopyrrole Containing Conjugated Random Copolymers for Organic Solar Cell Applications.

In this study, six different donor-π-acceptor1-π-donor-acceptor2 type random co-polymers containing benzodithiophene as a donor, benzooxadiazole (BO), and thieno[3,4-c]pyrrole-4,6-dione (TPD) as acceptor, have been synthesized and characterized. In addition to the acceptor core ratio at different values, the effect of aromatic bridge structures on the optical, electronic, and photovoltaic properties of six different random co-polymers is investigated by using thiophene and selenophene structures as aromatic bridge units. To investigate how the acceptor unit ratio and replacement of aromatic bridge units impact the structural, electronic, and optical properties of the polymers, density functional theory (DFT) calculations are carried out for the tetramer models. The open-circuit voltage (VOC), which is strongly correlated with the HOMO levels of the donor material, is enhanced with the increasing ratio of the TPD moiety. On the other hand, the short-circuit current (JSC), which is associated with the absorption ability of the donor material, is improved by the increasing ratio of BO moiety with the π-bridges. BO moiety dominant selenophene π-bridged co-polymer (P4) showed the best performance with a power conversion efficiency (PCE) of 6.26%, a JSC of 11.44mAcm2, a VOC of 0.80V, and a fill factor (FF) of 68.81%.

Material and Application of Semitransparent Organic Solar Cells

Material and Application of Semitransparent Organic Solar Cells

Simultaneously Improving Stretchability and Efficiency of Flexible Organic Solar Cells by Incorporating a Copolymer Interlayer in Active Layer

AbstractMechanical stretchability is a vital criterion for the wearable application of organic solar cells (OSCs), while the excessive rigidity of fused‐ring small molecular acceptors make the photovoltaic film hard to meet the stretchable requirements. Herein, an effective strategy is developed to construct an intrinsically stretchable active layer by inserting copolymer PM6‐b‐PYSe as an interlayer between layer‐by‐layer processed D18 and BTP‐eC9. The copolymer interlayer shunts the penetration of BTP‐eC9 and facilitates an appropriate phase separation, favoring the enhanced crack onset strain of 17.69% compared to the D18/BTP‐eC9 film (9.67%). Combining with the optimal energy levels, prolonged carrier lifetime, and suppressed bimolecular recombination aroused by the incorporation of PM6‐b‐PYSe, the D18/PM6‐b‐PYSe/BTP‐eC9‐based OSC yields an encouraging efficiency of 17.97%. In particular, the device demonstrates excellent mechanical property, which can retain over 80% after 4000 bending cycles. This work provides an effective strategy to simultaneously enhance the intrinsic mechanical stretchability and photovoltaic performance of flexible OSCs.

Strategies to Enhance the Stability of Non‐Fullerene Acceptor‐Based Organic Solar Cells

AbstractThrough comprehensive density functional theory calculations, the photodegradation mechanisms, including cis–trans isomerization, electrocyclization, and sigmatropic rearrangement reactions are investigated in indacenodithieno [3,2‐b] thiophene (IT)‐based non‐fullerene acceptors (NFAs). Various functional group substitutions on the core (fluorine, ethyl, and cyano groups) and end groups (fluorine) of NFA are introduced to elucidate the influence of chemical modifications on photodegradation pathways. The findings reveal that the core substitution can effectively suppress electrocyclization and 1,5‐sigmatropic shift reactions, which are major contributors to photodegradation. Furthermore, the electronic, excited‐state, and charge transport properties of pristine and degraded products are studied to gain insights into the impact of degradation on photovoltaic parameters. The results suggest that photodegradation leads to the formation of shallow energy trap states, hindering charge transport and increasing charge recombination, ultimately affecting the power conversion efficiency of organic solar cells (OSCs). The study not only provides a comprehensive understanding of photodegradation mechanisms but also offers valuable molecular design strategies to enhance the stability of NFAs for future large‐scale applications of OSCs. By establishing a clear connection between the chemical structure and photostability of NFA, this research represents a pivotal contribution to the field of organic electronics and sustainable energy technologies.