Efficient Organic Solar Cells Research Articles

Does the substrate and a buffer layer have a greater influence on poly(3-Hexylthiophene) films deposited by the chronocoulometry technique?

Abstract In this study, we investigate the interface morphology and optical properties of electrochemical poly(3-hexylthiophene) (P3HT) films deposited by electrochemical synthesis using the chronocoulometry technique on tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO) and how the substrate used influences in the deposition of the films and their optical and morphological properties, as well as the buffer layer and the interface effect, with and without spin-coating films of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). P3HT polymeric films were synthesized and deposited via the oxidation of the 3-hexylthiophene (3-HT) monomer and characterized via Raman spectroscopy. The morphology and thickness of the P3HT layer present in the samples ITO/P3HT, FTO/P3HT, ITO/PEDOT:PSS/P3HT, and FTO/PEDOT:PSS/P3HT were carried out using atomic force microscopy (AFM). The optical and electronic gap energy of P3HT were calculated from UV‒Vis spectra and cyclic voltammetry curves, respectively. The photoluminescence (PL) spectra showed broad and asymmetrical line shapes fitted by multi-Gaussian functions identifying different emission species. Emission ellipsometry spectroscopy was performed to study the energy transference between adjacent polymer chains. Our results show a higher linear polarized light emitted by ITO/PEDOT:PSS/P3HT film, ∼37%, thus demonstrating a significant decrease in the energy transfer. Based on these results, the efficiency of organic solar cells can be improved via the interaction of the polymer/polymer interface.

Integrated Omnidirectional Design of Non‐Volatile Solid Additive Enables Binary Organic Solar Cells with Efficiency Exceeding 19.5 %

AbstractSolid additives have drawn great attention due to their numerous appealing benefits in enhancing the power conversion efficiencies (PCEs) of organic solar cells (OSCs). To date, various strategies have been reported for the selection or design of non‐volatile solid additives. However, the lack of a general design/evaluation principles for developing non‐volatile solid additives often results in individual solid additives offering only one or two efficiency‐boosting attributes. In this work, we propose an integrated omnidirectional strategy for designing non‐volatile solid additives. By validating the method on the 4,5,9,10‐pyrene diimide (PyDI) system, a novel non‐volatile solid additive named PyMC5 was designed. PyMC5 is capable of enhancing device performance by establishing synergistic dual charge transfer channels, forming appropriate interactions with active layer materials, reducing non‐radiative voltage loss and optimizing film morphology. Notably, the binary device (PM6 : L8‐BO) treated by PyMC5 achieved a PCE over 19.5 %, ranking among the highest reported to date. In addition, the integration of PyMC5 mitigated the degradation process of the devices under photo‐ and thermal‐stress conditions. This work demonstrates an efficient integrated omnidirectional approach for designing non‐volatile solid additives, offering a promising avenue for further advancements in OSC development.

Integrated Omnidirectional Design of Non-Volatile Solid Additive Enables Binary Organic Solar Cells with Efficiency Exceeding 19.5 .

Solid additives have drawn great attention due to their numerous appealing benefits in enhancing the power conversion efficiencies (PCEs) of organic solar cells (OSCs). To date, various strategies have been reported for the selection or design of non-volatile solid additives. However, the lack of a general design/evaluation principles for developing non-volatile solid additives often results in individual solid additives offering only one or two efficiency-boosting attributes. In this work, we propose an integrated omnidirectional strategy for designing non-volatile solid additives. By validating the method on the 4,5,9,10-pyrene diimide (PyDI) system, a novel non-volatile solid additive named PyMC5 was designed. PyMC5 is capable of enhancing device performance by establishing synergistic dual charge transfer channels, forming appropriate interactions with active layer materials, reducing non-radiative voltage loss and optimizing film morphology. Notably, the binary device (PM6 : L8-BO) treated by PyMC5 achieved a PCE over 19.5 %, ranking among the highest reported to date. In addition, the integration of PyMC5 mitigated the degradation process of the devices under photo- and thermal-stress conditions. This work demonstrates an efficient integrated omnidirectional approach for designing non-volatile solid additives, offering a promising avenue for further advancements in OSC development.

Conjugated Group Tuning of Self‐Assembled Monolayer for Efficient Hole‐Transport Layer in Organic Solar Cells

AbstractP‐type carbazole‐derived self‐assembled monolayers (SAMs) have garnered significant attention as promising hole transport layers (HTLs) in the development of highly efficient organic solar cells (OSCs). However, it still lacks the effective navigation to modulate the terminal functional groups of SAMs to achieve a compromise between the highest occupied molecular orbital (HOMO) energy levels and self‐aggregation behavior. Herein, the terminal functional groups are adjusted and three SAMs are synthesized, namely, t‐Bu‐3PACz, Ph‐3PACz, and Bz‐3PACz to comprehensively investigate their intrinsic properties and influence on photovoltaic performance. Among them, Ph‐3PACz featuring an exceptionally suitable conjugated region and steric hindrance exhibits the best compatibility with the active layer, superior electrical conductivity, HOMO energy level aligning with polymer donor, and ordered film packing. As a result, the photovoltaic devices based on Ph‐3PACz exhibit an open‐circuit voltage (VOC) of 0.850 V, a short‐circuit current density (JSC) of 28.7 mA cm−2, and a fill factor (FF) of 78.5%, thus resulting in a remarkable power conversion efficiency (PCE) of 19.2%. This work provides an effective and easily navigable method to modulate the molecular packing and energy levels of SAMs, thereby achieving highly efficient OSCs.

Fluorination or Not in Small Molecule Solar Cells: Achieving a Higher Efficiency with Halogen-Free End Group.

Fluorination is an efficient strategy for improving organic solar cells (OSCs) efficiency, particularly by fluorinating the end group of emerging nonfullerene acceptors. Here, the fluorination effect was investigated by using small molecule donors with fluorine-free (SBz) and fluorinated (SBz-F) end groups, paired with the emerging nonfullerene acceptor Y6. Interestingly and unexpectedly, fluorination of the end group negatively affects OSCs efficiency, with fluorine-free SBz:Y6 OSCs achieving a higher power conversion efficiency (PCE) of 11.05 % compared to the fluorine-containing SBz-F:Y6 blends (PCE=9.61 %). Analysis of space-charge limited currents reveals lower and unbalanced hole/electron mobility in SBz-F:Y6 compared to the SBz:Y6 blends. These findings are further supported by charge recombination dynamics and donor-acceptor miscibility analyses.

Regiospecific Incorporation of Fluorine Atoms in Polythiophene Derivatives for Efficient Organic Solar Cells.

Derivatives of polythiophene (PT) have garnered considerable attention in organic solar cells (OSCs) because of their relatively uncomplicated molecular structures and cost-effective synthesis. Herein, we have developed two regioisomeric fluorinated PT donors, PEI3T-FITVT and PEI3T-FOTVT, to realize efficient OSCs. PEI3T-FITVT and PEI3T-FOTVT are strategically designed with different fluorine atom arrangements on thiophene-vinyl-thiophene (TVT) units. Notably, PEI3T-FOTVT possesses enhanced backbone planarity induced by F···S noncovalent interactions between two constituent building blocks. Consequently, PEI3T-FOTVT with the higher aggregation and crystalline properties leads to a 2.5-fold increase in hole mobility over PEI3T-FITVT (from 1.4 × 10-4 to 3.6 × 10-4 cm2 V-1 s-1). Furthermore, PEI3T-FOTVT exhibits higher domain purity than PEI3T-FITVT, leading to faster charge transport and reduced charge recombination in OSC devices. These characteristics lead to a higher power conversion efficiency of 14.4% for PEI3T-FOTVT-based OSCs, compared to 12.9% for PEI3T-FITVT-based OSCs.

Rebuilding Peripheral F, Cl, Br Footprints on Acceptors Enables Binary Organic Photovoltaic Efficiency Exceeding 19.7.

Given homomorphic fluorine, chlorine and bromine atoms are featured with gradually enlarged polarizability/atomic radius but decreased electronegativity, the rational screen of halogen species and location on small molecular acceptors (SMAs) is quite essential for acquiring desirable molecular packing to boost efficiency of organic solar cells (OSCs). Herein, three isomeric SMAs (CH-F, CH-C and CH-B) are constructed by delicately rebuilding peripheral F, Cl, Br footprints on both central and end units. Such a re-permutation of peripheral halogens could not only maintain the structural symmetry of SMAs to the maximum, but also acquire extra asymmetric benefits of enhanced dipole moment and intramolecular charge transfer, etc. Moreover, central brominating enhances molecular crystallinity of CH-B without introducing undesirable steric hindrance on end groups, thus rendering a better balance between high crystallization and domain size control in PM6:CH-B blend. Further benefitting from the large dielectric constant, small exciton binding energy, optimized molecular packing and great electron transfer integral, CH-B affords the first class binary OSC efficiency of 19.78%, moreover, the highest efficiency of 18.35% thus far when increasing active layer thickness to ~300 nm. Our successful screening in rebuilding peripheral halogen footprints provides the valuable insight into further rational design of SMAs for record-breaking OSCs.

Rebuilding Peripheral F, Cl, Br Footprints on Acceptors Enables Binary Organic Photovoltaic Efficiency Exceeding 19.7%

Given homomorphic fluorine, chlorine and bromine atoms are featured with gradually enlarged polarizability/atomic radius but decreased electronegativity, the rational screen of halogen species and location on small molecular acceptors (SMAs) is quite essential for acquiring desirable molecular packing to boost efficiency of organic solar cells (OSCs). Herein, three isomeric SMAs (CH‐F, CH‐C and CH‐B) are constructed by delicately rebuilding peripheral F, Cl, Br footprints on both central and end units. Such a re‐permutation of peripheral halogens could not only maintain the structural symmetry of SMAs to the maximum, but also acquire extra asymmetric benefits of enhanced dipole moment and intramolecular charge transfer, etc. Moreover, central brominating enhances molecular crystallinity of CH‐B without introducing undesirable steric hindrance on end groups, thus rendering a better balance between high crystallization and domain size control in PM6:CH‐B blend. Further benefitting from the large dielectric constant, small exciton binding energy, optimized molecular packing and great electron transfer integral, CH‐B affords the first class binary OSC efficiency of 19.78%, moreover, the highest efficiency of 18.35% thus far when increasing active layer thickness to ~300 nm. Our successful screening in rebuilding peripheral halogen footprints provides the valuable insight into further rational design of SMAs for record‐breaking OSCs.

Correction: A theoretical approach for investigating the end-capped engineering effect on indophenine-based core for efficient organic solar cells

Correction: A theoretical approach for investigating the end-capped engineering effect on indophenine-based core for efficient organic solar cells

A Mixed-Pure Planar Heterojunction Structure of Active Layers for Efficient Sequential Blade-Coating Organic Solar Cells.

Precise modulating the vertical structure of active layers to boost charge transfer is an effective way to achieve high power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, efficient OSCs with a well-controlled vertical structure are realized by a rapid film-forming method combining low boiling point solvent and the sequential blade-coating (SBC) technology. The results of grazing incident wide-angle X-ray scattering measurement show that the vertical component distribution is varied by changing the processing solvent. Novel characterization technique such as tilt resonant soft X-ray scattering is used to test the vertical structure of the films, demonstrating the dichloromethane (DCM)-processed film is truly planar heterojunction. The devices with chloroform (CF) processed upper layer show an increased mixed phase region compared to these devices with toluene (TL) or -DCM-, which is beneficial for improving charge generation and achieving a superior PCE of 17.36%. Despite significant morphological varies, the DCM-processed devices perform slightly lower PCE of 16.66%, which is the highest value in truly planar heterojunction devices, demonstrating higher morphological tolerance. This work proposes a solvent-regulating method to optimize the vertical structure of active layers through SBC technology, and provides a practical guidance for the optimization of the active-layer microstructure.

Precision Fluorine Functionalization in Alkyl Side Chains of Polymer Donors for Highly Efficient Organic Solar Cells

Precision Fluorine Functionalization in Alkyl Side Chains of Polymer Donors for Highly Efficient Organic Solar Cells

Incorporation of Graphene Oxide as Hole Transport Layer in PTB7:PC71BM/PFN:Br Pure Organic Solar Cells

Organic solar cells (OSCs) are preferred over inorganic solar cells because they are less expensive, lighter, and easier to manufacture. However, the power conversion efficiency of OSCs remains poor. One promising material for OSCs is PTB7:PC71BM, which has high electrical conductivity, solubility in various solvents, and the ability to be deposited over large areas at low temperatures using cost-effective techniques. All photogenerated excitons must split at the interface between the acceptor and donor materials in order to achieve high quantum efficiency. Additionally, all generated charges must subsequently reach their respective electrodes. Due to its strong mechanical, electrical, thermal, and optical properties, graphene oxide (GO) is a great material for the Hole Transport Layer (HTL) in OSCs. In this study, GO was used as the HTL in PTB7:PC71BM organic solar cells and the effect of GO on these OSCs were examined. SCAPA-1D simulation software was used to simulate the organic solar cells. The thickness of absorber layer has been optimised to be 400nm. We found that GO can improve the efficiency of OSCs by facilitating the dissociation of excitons and by improving the charge transport properties of the device. Our findings imply that GO is a potentially useful material for increasing OSC efficiency.

Reducing Non-Radiative Energy Losses in Non-fullerene Organic Solar Cells.

With the rapid advancement of non-fullerene acceptors (NFAs), the power conversion efficiency (PCE) of organic solar cells (OSCs) has surpassed the 20% threshold, highlighting their considerable potential as next-generation energy conversion devices. In comparison to inorganic or perovskite solar cells, the open-circuit voltage (Voc) of OSCs is constrained by substantial non-radiative energy losses (ΔEnr), leading to values notably below those anticipated by the Shockley-Queisser limit. In OSCs, non-radiative energy losses are intimately associated with the electroluminescent quantum efficiency (EQEEL) of charge transfer states, which is in turn directly affected by the photoluminescence quantum yield (PLQY) of acceptor materials. Consequently, enhancing the PLQY of low-bandgap acceptor materials has emerged as a pivotal strategy to effectively mitigate ΔEnr. This review article delves into the intrinsic correlation between molecular structure and PLQY from the vantage point of acceptor material design. It further explores methodologies for designing acceptor materials exhibiting high PLQY, with the ultimate goal of realizing OSCs that combine high efficiency with minimal ΔEnr.

20.4% Power conversion efficiency from albedo-collecting organic solar cells under 0.2 albedo.

Highly efficient bifacial organic solar cells (OSCs) have not been reported due to limited thickness of the active layer in conventional configurations, not allowing for efficient harvesting of front sunlight and albedo light. Here, bifacial OSCs are reported with efficiency higher than the monofacial counterparts. The incorporation of pyramid-based asymmetrical optical transmission (AOT) array to a transparent silver electrode suppresses the escaping of front sunlight without sacrificing the harvesting of albedo light. Parasitic absorption induced by the excitation of surface plasmons in an AOT electrode is further reduced by doping organic emitter in electron transport layer and capping high dielectric constant film to silver. The rear electrode achieves a front transmittance of 7% and a rear transmission of 86%. At a conventional albedo of 0.2, the synergistic effect of AOT and minimized optical loss endow the bifacial OSCs with power conversion efficiency of 20.4%. This work paves the way for the utilization of albedo light in OSCs.

Enhancing the photovoltaic performance of dithienobenzodithiophene based polymer donors through backbone fluorination and radical polymer additives

Unveiling the corresponding relationship between the molecular architecture of organic semiconductor materials and the morphology within the active layer of the organic solar cells (OSCs) is essential for the innovation of novel optical materials and the refinement of device optimization strategies to overcome the bottlenecks in efficiency. In this work, three dithieno[3,2-b]benzo[1,2-b;4,5-b’]dithiophene(DTBDT)-alt-benzothiadiazole (BT) based polymer donors (PDTBDT-F-BT, PDTBDT-F-FBT, and PDTBDT-F-2FBT) with varying fluorine atom content within their acceptor segments were designed and synthesized, and the photovoltaic performances of these polymers when blended with Y6 were meticulously investigated. Incorporating fluorine atoms into the BT segment was observed to not only incrementally increase the optical bandgap, lower the HOMO energy level, and bolster the self-aggregation of the polymer, but also effectively reduce the surface energy of the resulting polymer, thereby altering the donor-acceptor (D-A) interfacial spacing and the phase separation in the blend films as illustrated by molecular dynamic simulations and morphology characterization. As a result, the OSCs fabricated using PDTBDT-F-FBT, which incorporates a single fluorine substitution in the BT unit, demonstrated the highest power conversion efficiency (PCE) of 9.92 %. More importantly, this blend film's morphology is likely to be more conducive to the incorporation of the radical polymer additive, GDTA. This has resulted in a notable reduction in voltage loss, ultimately achieving a higher PCE of 11.55 % for the PDTBDT-F-FBT:Y6 based OSCs. This research uncovered a synergistic impact of backbone fluorination and the incorporation of radical polymer additives, which contributed to reducing the energy loss and enhancing the efficiency of OSCs from DTBDT-based polymer donors.

Isomeric Dimer Acceptors for Stable Organic Solar Cells with over 19 % Efficiency

AbstractThe strategy of isomerization is known for its simple yet effective role in optimizing molecular configuration and enhancing the power conversion efficiency (PCE) of organic solar cells (OSCs). However, the impact of isomerization on the design of dimer acceptors has been rarely investigated, and the relationship between the chemical structure and optoelectronic property remains unclear. In this study, we designed and synthesized two dimer acceptor isomers named D‐TPh and D‐TN, which differ in the positional arrangement of their end capping groups. Compared to D‐TN, D‐TPh exhibited enhanced backbone planarity, elevated lowest unoccupied molecular orbital energy level, and more ordered molecular stacking. Consequently, the OSC device based on PM6 : D‐TPh achieved a PCE of 19.05 %, higher than that (PCE=18.42 %) of the device based on PM6 : D‐TN. Large‐area PM6 : D‐TPh devices (1 cm2) yielded a PCE of 18.00 %. More importantly, the extrapolated T80 lifetime of the PM6 : D‐TPh device is over 2800 h with MPP tracking under continuous one‐sun illumination. These results suggest that isomerization strategy is an effective way to optimize the molecular configuration of dimer acceptors for the fabrication of high‐efficiency and stable OSCs.

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.

Unraveling the impacts of intermolecular interaction on morphology evolution for highly efficient organic solar cells and modules

Unraveling the impacts of intermolecular interaction on morphology evolution for highly efficient organic solar cells and modules

Theoretical study of star shaped benzotriindole based variant non-fullerene acceptors for efficient organic solar cells

Theoretical study of star shaped benzotriindole based variant non-fullerene acceptors for efficient organic solar cells

Regulating Electron‐Phonon Coupling by Solid Additive for Efficient Organic Solar Cells

AbstractStrong electron‐phonon coupling can hinder exciton transport and induce undesirable non‐radiative recombination, resulting in a shortened exciton diffusion distance and constrained exciton dissociation in organic solar cells (OSCs). Therefore, suppressing electron‐phonon coupling is crucially important for achieveing high‐performance OSCs. Here, we employ the solid additive to regulating electron‐phonon coupling in OSCs. The planar configuration of SA1 confers a significant advantage in suppressing lattice vibrations in the active layers, reducing the scattering of excitons by phonons. Consequently, a slow but sustained hole transfer process is identified in the SA1‐assisted film, indicating an enhancement in hole transfer efficiency. Prolonged exciton diffusion length and exciton lifetime are achieved in the blend film processed with SA1, attributed to a low non‐radiative recombination rate and low energetic disorder for charge carrier transport. As a result, a high efficiency of 20 % was achieved for ternary device with a remarkable short‐circuit current. This work highlights the important role of suppressing electron‐phonon coupling in improving the photovoltaic performance of OSCs.