High Performance Organic Photovoltaics Research Articles

An ultraflexible energy harvesting-storage system for wearable applications

The swift progress in wearable technology has accentuated the need for flexible power systems. Such systems are anticipated to exhibit high efficiency, robust durability, consistent power output, and the potential for effortless integration. Integrating ultraflexible energy harvesters and energy storage devices to form an autonomous, efficient, and mechanically compliant power system remains a significant challenge. In this work, we report a 90 µm-thick energy harvesting and storage system (FEHSS) consisting of high-performance organic photovoltaics and zinc-ion batteries within an ultraflexible configuration. With a power conversion efficiency surpassing 16%, power output exceeding 10 mW cm–2, and an energy density beyond 5.82 mWh cm–2, the FEHSS can be tailored to meet the power demands of wearable sensors and gadgets. Without cumbersome and rigid components, FEHSS shows immense potential as a versatile power source to advance wearable electronics and contribute toward a sustainable future.

A Difluoro-Methoxylated Ending-Group Asymmetric Small Molecule Acceptor Lead Efficient Binary Organic Photovoltaic Blend.

Developing a new end group for synthesizing asymmetric small molecule acceptors (SMAs) is crucial for achieving high-performance organic photovoltaics (OPVs). Herein, an asymmetric small molecule acceptor, BTP-BO-4FO, featuring a new difluoro-methoxylated end-group is reported. Compared to its symmetric counterpart L8-BO, BTP-BO-4FO exhibits an upshifted energy level, larger dipole moment, and more sequential crystallinity. By adopting two representative and widely available solvent additives (1-chloronaphthalene (CN) and 1,8-diiodooctane (DIO)), the device based on PM6:BTP-BO-4FO (CN) photovoltaic blend demonstrates a power conversion efficiency (PCE) of 18.62% with an excellent open-circuit voltage (VOC) of 0.933V, which surpasses the optimal result of L8-BO. The PCE of 18.62% realizes the best efficiencies for binary OPVs based on SMAs with asymmetric end groups. A series of investigations reveal that optimized PM6:BTP-BO-4FO film demonstrates similar molecular packing motif and fibrillar phase distribution as PM6:L8-BO (DIO) does, resulting in comparable recombination dynamics, thus, similar fill factor. Besides, it is found PM6:BTP-BO-4FO possesses more efficient charge generation, which yields better VOC-JSC balance. This study provides a new ending group that enables a cutting-edge efficiency in asymmetric SMA-based OPVs, enriching the material library and shed light on further design ideas.

Layer-optimized Cd0.85PS3Li0.15H0.15 triggering donor crystallization for high performance organic photovoltaics with nuclear radiation shielding

Despite the recognized potential of two-dimensional crystals in organic photovoltaics (OPVs), a comprehensive understanding of layer-dependent doping effects remains elusive. Here, we employed liquid-phase exfoliation to synthesize various layers of novel metal phosphorus tri-chalcogenide (TMPTC), Cd0.85PS3Li0.15H0.15. Molecular dynamics simulation shows that Cd0.85PS3Li0.15H0.15 tends to be distributed in the domain of D18. Although increasing the Cd0.85PS3Li0.15H0.15 layer can improve its ability to adsorb D18, it will also form a larger steric hindrance in the domain of D18. The 2L Cd0.85PS3Li0.15H0.15 has balanced adsorption capacity and steric hindrance, maximally inducing the crystallinity of D18, thus significantly promoting the charge transport and effectively suppressing the bulk charge recombination in D18:L8-BO devices. Consequently, the power conversion efficiency (PCE) of D18:L8-BO-based OPVs experienced a significant boost from 17.57 % to 19.59 %. In addition, the Cd0.85PS3Li0.15H0.15 dopants can enhance the nuclear radiation shielding ability of OPVs, which can provide the theoretical and experimental basis for developing two-dimensional TMPTCs dopants toward OPVs with nuclear radiation shielding.

Self-Assembled Interlayer Enables High-Performance Organic Photovoltaics with Power Conversion Efficiency Exceeding 20.

Interfacial layers (ILs) are prerequisites to form the selective charge transport for high-performance organic photovoltaics (OPVs) but mostly result in considerable parasitic absorption loss. Trimming the ILs down to a mono-molecular level via the self-assembled monolayer is an effective strategy to mitigate parasitic absorption loss. However, such a strategy suffers from inferior electrical contact with low surface coverage on rough surfaces and poor producibility. To address these issues, here, the self-assembled interlayer (SAI) strategy is developed, which involves a thin layer of 2-6nm to form a full coverage on the substrate via both covalent and van der Waals bonds by using a self-assembled molecule of 2-(9H-carbazol-9-yl) (2PACz). Via the facile spin coating without further rinsing and annealing process, it not only optimizes the electrical and optical properties of OPVs, which enables a world-record efficiency of 20.17% (19.79% certified) but also simplifies the tedious processing procedure. Moreover, the SAI strategy is especially useful in improving the absorbing selectivity for semi-transparent OPVs, which enables a record light utilization efficiency of 5.34%. This work provides an effective strategy of SAI to optimize the optical and electrical properties of OPVs for high-performance and solar window applications.

Achieving High Fill Factor in Organic Photovoltaic Cells by Tuning Molecular Electrostatic Potential Fluctuation.

In the field of organic photovoltaics (OPVs), significant progress has been made in tailoring molecular structures to enhance the open-circuit voltage and the short-circuit current density. However, there remains a crucial gap in the development of coordinated material design strategies focused on improving the fill factor (FF). Here, we introduce a molecular design strategy that incorporates electrostatic potential fluctuation to design organic photovoltaic materials. By reducing the fluctuation amplitude of IT-4F, we synthesized a new acceptor named ITOC6-4F. When using PBQx-TF as a donor, the ITOC6-4F-based cell shows a markedly low recombination rate constant of 0.66×10-14 cm3 s-1 and demonstrates an outstanding FF of 0.816, both of which are new records for binary OPV cells. Also, we find that a small fluctuation amplitude could decrease the energetic disorder of OPV cells, reducing energy loss. Finally, the ITOC6-4F-based cell creates the highest efficiency of 16.0 % among medium-gap OPV cells. Our work holds a vital implication for guiding the design of high-performance OPV materials.

Hexylation Stabilises Twisted Backbone Configurations in the Prototypical Low-Bandgap Copolymer PCDTBT.

Conjugated donor-acceptor copolymers hold great potential as materials for high-performance organic photovoltaics, organic transistors and organic thermoelectric devices. Their low optical bandgap is achieved by alternation of donor and acceptor moieties along the polymer chain, leading to a pronounced charge-transfer character of electronic excitations. However, the influence of appended side chains and of chemical defects of the backbone on their photophysical and conformational properties remains largely unexplored on the level of individual chains. Here, we employ room temperature single-molecule photoluminescence spectroscopy on four compounds based on the prototypical copolymer PCDTBT with systematically changed chemical structure. Our results show that an increasing density of statistically added hexyl chains to the TBT comonomer distorts the molecular conformation, likely through the increase of average dihedral angles along the backbone. We find that, although the conformation becomes more twisted with high hexyl density, the side chains appear to stabilize the backbone in this twisted conformation. In addition, we demonstrate that homocoupling defects along the backbone barely influence the PL spectra of single chains, and thus intra-chain electronic properties.

Stretchable and transparent nanopillar arrays for high-performance ultra-flexible organic photovoltaics

Ultra-flexible organic photovoltaic (OPV) devices are gaining recognition due to their lightweight, mechanical flexibility, and high productivity potential and are emerging as a notable alternative power source. Significant enhancements in material design and device architecture have facilitated a near 20% of power conversion efficiencies (PCEs). To elevate PCE further, the integration of soft optical elements is pivotal, enabling optimized photon utilization by minimizing reflection and augmenting the optical path through diffraction. In this research, we showcase an ultra-flexible energy harvesting system embedding thin, stretchable nanopillar arrays made of poly(dimethylsiloxane). The unique diffraction and interference from nanopillar arrays amplify the photogeneration of exciton pairs, which, in turn, boosts the current density of PM6:Y6 based OPV devices from 25.46 to 28.01 mA/cm2, resulting in a PCEmax of 15.92%. Furthermore, the exceptional flexibility of this mold was demonstrated on an ultra-flexible PM6:Y6 device, enduring 100% compressive strain through 1000 repeated tests. These results propose an advantageous approach for improving OPV efficiency without necessitating alterations to the inherent components or structures of the device.

Synergistically optimizing the optoelectronic properties and morphology using a photo-active solid additive for high-performance binary organic photovoltaics

This work explores a new solid additive with TADF properties for high-performance OPVs. The TADF additive fine-tunes the morphology and enhances exciton diffusion and dissociation, resulting in an efficiency of 19.4%, making it one of the top binary OPVs.

Embedded Host/Guest Alloy Aggregations Enable High-Performance Ternary Organic Photovoltaics.

Ternary strategy has been intensively studied to improve the power conversion efficiencies of organic photovoltaics. Thereinto, the location of the guest component plays a critical role, but few reports have devoted to this concern. Hereon, we disclose the distribution of LA1 as guest acceptor in varieties of ternary scenarios, and outline the dominating driving forces of managing the guest distribution and operating modes. Governed by appropriate relationship of compatibility, crystallinity, and surface energies between host and guest acceptors, as well as interfacial interactions between donor and dual acceptors, most of the LA1 molecules permeate into the internal of host acceptor phases, forming embedded host/guest alloy-like aggregations. The characteristic distributions greatly optimize the morphologies, maximize energy transfer, and enhance exciton/charge behaviors. Particularly, PM6:IT-4F:LA1 ternary cells afford high efficiency of 15.27% with impressive fill factors (FF) over 81%. The popularization studies further verify the superiority of the LA1-involved alloy structures, and with Y6-family acceptor as host component, an outstanding efficiency of 19.17% was received. The results highlight the importance of guest distribution in ternary systems, and shed light on the governing factors of distributing the guests in ternary cells. This article is protected by copyright. All rights reserved.

Atomic layer deposition-processed laminated In2O3:V2O5 nanocompounds: Versatile electrode platforms for high-performance organic photovoltaics and capacitor devices

Despite considerable advancements in transparent conductive electrodes (TCEs), their widespread use in energy storage and conversion devices remains limited. This is primarily attributable to factors such as the work function (WF), surface roughness, and charge mobility limitations. These challenges necessitate comprehensive solutions and innovative approaches to utilize TCEs for energy-related applications. Herein, In2O3:V2O5 nanocompound TCEs were fabricated with excellent transmittance (∼ 90%), high WF (5.33 eV), and large mobility (52.1 cm2/V·s) using atomic layer deposition. The performance of the In2O3:V2O5 nanocompound TCE was evaluated in organic photovoltaics (OPVs) and metal-insulator-metal (MIM) capacitors. In OPVs based on the PM6:Y6 active layer, a low surface roughness and suitable energy level alignment of In2O3:V2O5 nanocompound TCEs with the active layer eliminate the requirement of a hole-transport layer (HTL), resulting in an efficiency of 16.3% and an excellent fill-factor of 71.0% in HTL-free OPVs under simulated 1-sun illumination. Moreover, in MIM capacitor devices that employ the TiO2 dielectric, In2O3:V2O5 nanocompound TCEs exhibit a significantly lower leakage current (> 1800 times) and improved capacitance (2.5 times) compared with those of conventional TiN electrode-based capacitors. The dual functionality of the proposed In2O3:V2O5 nanocompound TCEs validates their potential for use in several optoelectronic devices.

Long-Range Charge Separation Enabled by Intramoiety Delocalized Excitations in Copolymer Donors in Organic Photovoltaic Blends.

For over two decades, most high-performance organic photovoltaics (OPVs) have been made with donor:acceptor bulk heterojunctions with domain sizes limited by exciton diffusion, where charge separation mostly takes place through the dissociation of the interfacial charge-transfer (xCT) excitons. Recently, nonfullerene acceptor (NFA)-based OPVs have shown excellent compatibility to device structures with large domains in active layers. However, it remains elusive how the excitations that are distant from the interfaces are converted into free charges. Here, we report the identification of a new charge separation channel in model copolymer/NFA blends mediated by intra-moiety delocalized excitations in both planar heterojunctions and donor-enriched bulk heterojunctions. The delocalized excitations induced by interchromophore electronic interactions in copolymer donors mediate the long-range charge separation and dissociate into free charges without forming the bound xCT states first, releasing the constraints associated with the short exciton diffusion length in organic materials. The long-range charge separation mechanism uncovered in this work, in cooperation with the short-range xCT-mediated pathway, holds the potential to further optimize OPVs with diverse device structures.

Sensitive near-infrared circularly polarized light detection via non-fullerene acceptor blends

Circularly polarized light (CPL) is widely used for various applications in sensing and imaging1–3. An ongoing challenge is to realize high-quality CPL detection using chiral organic semiconductors, especially in the near-infrared (NIR) region4. Chiral molecules tend to rely on twisted stereogenic moieties; however, conventional approaches to reduce the bandgap of organic semiconductors are based on the use of co-planar backbones that commonly lead to molecular symmetries preventing chirality. Here we report a widely applicable strategy to directly induce chiroptical activity in planar non-fullerene acceptors5–7, which are widely used for high-performance organic photovoltaics and provide a wealth of opportunities to fill the spectral gap of CPL detection in the NIR regime. We demonstrate proof-of-concept circularly polarized organic photodiodes using chiroptically active non-fullerene acceptor blends, which exhibit strong circular dichroism and hence great sensitivity to CPL in the NIR region. Importantly, this strategy is found to be effective in a wide series of state-of-the-art non-fullerene acceptor families including ITIC5, o-IDTBR6 and Y6 analogues7, which substantially broadens the range of materials applicable to NIR CPL detection.

Indolocarbazole-based small molecules as guest donors for High-Performance ternary organic photovoltaics

This study explores the use of A-D-A or A-D-A′-type small molecule donors that contain an indolocarbazole-based moiety with both symmetric and asymmetric structures as the third component in PM6:Y6 systems to develop ternary organic photovoltaics (OPVs). The guest donor, Ema-OEt, was found to be highly miscible with Y6, resulting in an optimized morphology of an alloy-like structure in the blended film. This, in turn, led to balanced charge transport, high charge mobility, and low charge recombination in the devices, resulting in a synergistic improvement in PV parameters, ultimately leading to an advanced power conversion efficiency (PCE) of 17.64 % in the optimized (PM6:Ema-OEt:Y6 = 1: 0.07: 1.2) ternary device. Furthermore, despite having a higher HOMO energy level than PM6, Ema-OEt, doped as a guest donor in the ternary OPV device, demonstrated a remarkable indoor PCE of 28.67 % under TL84 (Pin = 311.9 μW cm−2). These findings provide an effective and innovative approach to enhance the performance of OPVs.

Critical Progress of Polymer Solar Cells with a Power Conversion Efficiency over 18%

The power conversion efficiencies (PCEs) of organic photovoltaics (OPVs) have reached more than 19%, along with the prosperous development of materials and device engineering. It is meaningful to make a comprehensive review of the research of OPVs for further performance improvement. In this review, some typical materials of high-performance OPVs are summarized, including representative polymer donor materials, non-fullerene acceptor materials, and interfacial modification materials, as well as their design rules for molecular engineering. From the point of view of device engineering, active layer treatment and deposition technology are introduced, which can play a critical role in adjusting the degree of molecular aggregation and vertical distribution. Meanwhile, a ternary strategy has been confirmed as an efficient method for improving the performance of OPVs, and the multiple roles of the appropriate third component in the photo-electronic conversion process are emphasized and analyzed. The challenges and perspectives concerning this region are also put forward for further developing high-performance OPVs.

Rhodanine-Based Non-Fullerene Acceptors for Organic Solar Cells with a High Open-Circuit Voltage of 1.07 V

To overcome the intrinsic limitations of fullerene-based organic photovoltaic (OPV) devices, research on OPV devices based on non-fullerene acceptors (NFAs) has been actively conducted in recent years. It is important to understand the relationship between the structure of the NFAs and photovoltaic properties to create high-performance OPV devices. In this study, we have designed and synthesized a series of NFAs (DFDO-RC2 and DFDE-RC2) based on electron-rich dithienosilole (D) and electron-deficient difluorobenzodiathiazole (F), benzodiathiazole-connected 3-ethylrhodanine (RC2) units, and alkyl chains of 2-ethylhexyl (E) and octyl (O) groups. The PTB7-Th:DFD-RC2 devices showed low PCEs mainly due to the highly located highest occupied molecular orbital (HOMO) energy levels of the DFD-RC2 acceptors compared to the PTB7-Th polymer donor. To lower the HOMO levels of the DFD-RC2 NFAs, the backbone structures were modified by replacing difluorobenzodiathiazole core moiety with difluorobenzene (FBz) to obtain DFBz-RC2 molecules (DFBzO-RC2 and DFBzE-RC2). PTB7-Th:DFBz-RC2 devices exhibited significantly improved PCEs compared to PTB7-Th:DFD-RC2 devices. The DFBzO-RC2 and DFBzE-RC2 molecule-based OPVs exhibited remarkably high Vocs of 1.03 and 1.07 V, respectively, which characteristic is associated with the very low energy loss (Eloss) of 0.51 eV in both PTB7-Th:DFBzO-RC2 and PTB7-Th:DFBzE-RC2 devices. Overall, our investigation of the various synthesized molecules reveals the structure-to-photovoltaic properties, which guide the design of new high-performance NFAs to advance in the field of organic solar cells.

Isomerization Directed Molecular Packing toward Suppressing Energy Loss in Nonfullerene Ternary Solar Cells

Organic semiconductors based upon conjugated frameworks are often isomeric and display distinct optoelectronic properties within minor structural variation. In this work, two isomeric nonfullerene acceptors (NFAs) ThMeCl-1 and ThMeCl-2, having the methyl and chlorine atoms attached on different positions of the electron-withdrawing end group, are synthesized and incorporated as the third component in ternary solar cells. Although these NFA isomers exhibit a similar bandgap, energy levels, and energy loss in their PM6 based binary devices, the efficiency enhancements in ternary devices differ significantly. Compared to ThMeCl-1, the incorporation of ThMeCl-2 in PM6:C5-16 solar cells enables less energy loss, leading to an extra 0.03 eV open-circuit voltage gain and a maximum efficiency increase from 17.8 to 18.9%. Grazing-incidence X-ray diffraction and molecular dynamics simulations reveal that this is attributed to the versatile intermolecular π–π stacking forms between ThMeCl-2 and the host NFA, which result in improved charge transport and suppressed recombination. This work provides a rational guidance for controlling the molecular packing in ternary systems to prepare high performance organic photovoltaics.

In Silico modeling and exploration of new acceptor molecules with enhanced power conversion efficiency for high-performance organic solar cell applications

Developing an effective strategy to increase open circuit voltage with maximum PCE is vital to realizing high-performance OPVs (organic photovoltaic). In this report, a novel class of non-fullerene acceptor compounds has been constructed by us (D2APH1 to D2APH4) for high-performance OPVs. End-capped alterations of the JC2 (R) molecules were formed using capable end-capped units. A high Fill factor with FF% has been achieved with PCE of 30.34% for D2APH1 to D2APH4. Redshift and a limited energy band gap relative to the reference molecule, a change in the absorption spectra have been observed for D2APH1 to D2APH4. Further, designed molecules also expressed enhanced open-circuit voltage values and strong electron and hole mobility across metal electrodes. Easy exciton excitation inside an excited state is caused by low excitation energy and strong oscillation strength. The different geometric, photovoltaic, and optoelectronic analyses indicated that engineered molecules provide capable contributions to the creation of highly effective OPVs.

Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance

The non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs.

Compromising Charge Generation and Recombination of Organic Photovoltaics with Mixed Diluent Strategy for Certified 19.4% Efficiency.

The ternary blend is demonstrated as an effective strategy to promote the device performance of organic photovoltaics (OPVs) due to the dilution effect. While the compromise between the charge generation and recombination remains a challenge. Here, a mixed diluent strategy for further improving the device efficiency of OPV is proposed. Specifically, the high-performance OPV system with a polymer donor, i.e., PM6, and a nonfullerene acceptor (NFA), i.e., BTP-eC9, is diluted by the mixed diluents, which involve a high bandgap NFA of BTP-S17 and a low bandgap NFA of BTP-S16 (similar with that of the BTP-eC9). The BTP-S17 of better miscibility with BTP-eC9 can dramatically enhance the open-circuit voltage (VOC ), while the BTP-S16 maximizes the charge generation or the short-circuit current density (JSC ). The interplay of BTP-17 and BTP-S16 enables better compromise between charge generation and recombination, thus leading to a high device performance of 19.76% (certified 19.41%), which is the best among single-junction OPVs. Further analysis on carrier dynamics validates the efficacy of mixed diluents for balancing charge generation and recombination, which can be further attributed to the more diverse energetic landscapes and improved morphology. Therefore, this work provides an effective strategy for high-performance OPV for further commercialization.

High-performance vertical field-effect organic photovoltaics

Limited by the inherent energy loss (Eloss) in carrier transport process, the device efficiency of organic solar cells shows inferior to traditional inorganic photovoltaic devices. Generally, molecular design, morphology optimization and interfacial engineering are usually required to alleviate Eloss. Here, vertical field-effect organic photovoltaic (VFEOPV) by integrating an bulk-heterojunction (BHJ) organic photovoltaic (OPV) with vertical field effect transistor (VFET) is invented, in which VFET generates a large, uneven, internal electric field, eliminating the requirement for driving force to dissociate excitons and prevents non-radiative recombination in OPV. In this way, the performance of solar cell can be well controlled by the gate voltage of VFET and the Eloss of VFEOPVs based on J71: ITIC system is dramatically reduced below 0.2 eV, significantly improving power conversion efficiency (PCE) from 10% to 18% under gate voltage of 0.9 V, which only causes negligible additional power consumption (~10−4mJ/cm2). Besides, the device also exhibits multi-functionality including transistor and phototransistors with excellent photodector performance. This work provides a new and general strategy to improve the OPV performance which is compatible with present optimization methods, and can be applied to improve PCE of other types of solar cells such as Perovskite and inorganic solar cells.