High-efficiency Organic Solar Cells Research Articles

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-bandgap 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 bandgap 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.

Mechanics manipulation in large-area organic solar modules achieving over 16.5 % efficiency

High-efficiency organic solar cells (OSCs) are typically produced through spin-coating, restricting their application to small areas. Blade-coating, however, emerging as a promising method for large-scale production, yet faces challenges in film morphology optimization, which often leads to reduced power conversion efficiency (PCE). This study delves into the influence of both liquid and solid additives on the morphology of active layer in blade-coated OSCs, comparing them with spin-coated counterparts, using the high-efficiency PM6:D18:BTP-eC9 active layer. For the first time, we discovered the distinct impacts of solid versus liquid additives on the film uniformity, phase separation and crystalline regulation in blade-coating technique. Our findings reveal that liquid additives in blade-coating trigger outward Marangoni flow, causing undesirable material aggregation and phase separation, thereby impairing device performances. Conversely, switching to solid additives, like 1,4-Diiodobenzene (DIB), prevents these detrimental changes in fluid mechanics and preserves the desired additive effects. We demonstrate that solid additives can significantly change these inferior behaviors introduced by liquid additives in blade-coating, regulate phase separation, enhance π-π accumulation and delay crystallization, and ultimately boost OSC efficiency. Using DIB solid additive, we achieved a PCE of 18.81 % in blade-coated devices. Scaling up by 252 times, the PCE of large-area OSC module (15.64 cm²) sustained at 16.70 % (certified 16.66 %), ranking among the highest efficiency for OSC modules reported so far. These modules also exhibited exceptional storage stability, retaining 98 % efficiency after 5880 h in a nitrogen atmosphere. This research also provides a comprehensive understanding from various film characterizations and the perspective of fluid mechanics normally lack in the research. This research not only establishes a new framework for high-performance and large-area OSC modules but also extends its findings to other OSC systems with different additives, demonstrating a roll-to-roll compatible technique.

Non-halogenated Solvent-Processed Organic Solar Cells with Approaching 20 % Efficiency and Improved Photostability.

The development of high-efficiency organic solar cells (OSCs) processed from non-halogenated solvents is crucially important for their scale-up industry production. However, owing to the difficulty of regulating molecular aggregation, there is a huge efficiency gap between non-halogenated and halogenated solvent processed OSCs. Herein, we fabricate o-xylene processed OSCs with approaching 20 % efficiency by incorporating a trimeric guest acceptor named Tri-V into the PM6:L8-BO-X host blend. The incorporation of Tri-V effectively restricts the excessive aggregation of L8-BO-X, regulates the molecular packing and optimizes the phase-separation morphology, which leads to mitigated trap density states, reduced energy loss and suppressed charge recombination. Consequently, the PM6:L8-BO-X:Tri-V-based device achieves an efficiency of 19.82 %, representing the highest efficiency for non-halogenated solvent-processed OSCs reported to date. Noticeably, with the addition of Tri-V, the ternary device shows an improved photostability than binary PM6:L8-BO-X-based device, and maintains 80 % of the initial efficiency after continuous illumination for 1380 h. This work provides a feasible approach for fabricating high-efficiency, stable, eco-friendly OSCs, and sheds new light on the large-scale industrial production of OSCs.

Guest Acceptors with Lower Electrostatic Potential in Ternary Organic Solar Cells for Minimizing Voltage Losses.

The ternary strategy, in which one guest component is introduced into one host binary system, is considered to be one of the most effective ways to realize high-efficiency organic solar cells (OSCs). To date, there is no efficient method to predict the effectiveness of guest components in ternary OSCs. Herein, three guest compositions (i.e., ANF-1, ANF-2 and ANF-3) with different electrostatic potential (ESP) are designed and synthesized by modulating the electron-withdrawing ability of the terminal groups through density functional theory simulations. The effects of the introduction of guest component into the host system (D18:N3) on the photovoltaic properties are investigated. The theoretical and experimental studies provide a key rule for guest acceptor in ternary OSCs to improve the open-circuit voltage, that is, the larger ESP difference between the guest and host acceptor, the stronger the intermolecular interactions and the higher the miscibility, which improves the luminescent efficiency of the blend film and the electroluminescence quantum yield (EQEEL) of the device by reducing the aggregation-caused-quenching, thereby effectively decreasing the non-radiative voltage loss of ternary OSCs. This work will greatly contribute to the development of highly efficient guest components, thereby promoting the rapid breakthrough of the 20% efficiency bottleneck for single-junction OSCs.

Selecting Solid Additives to Control the Interaction between Polymer Donors and Additives for Constructing High-Efficiency Organic Solar Cells

Selecting Solid Additives to Control the Interaction between Polymer Donors and Additives for Constructing High-Efficiency Organic Solar Cells

2,5-dichloro-3,4-diiodothiophene as a versatile solid additive for high-performance organic solar cells

Volatile solid additive (SA) with diverse chemical structures has been proved to be an alternative to prepare high-efficient organic solar cells (OSCs). While, various organic photovoltaic materials raise challenges in selecting suitable SAs during the device optimization. Herein, based on the simple and commonly used thiophene unit, we proposed a perhalogenated 2,5-dichloro-3,4-diiodothiophene (SA-T5) as the SA for the device optimizations. As results, the capacity of SA-T5 in optimizing molecular packings of small-molecular acceptor L8-BO, dimeric acceptor DL8, and polymeric acceptor PY-DT based blend films has been demonstated. Their optimized morphologies assisted by SA-T5 contribute to the suppressed charge recombination and enhanced charge transportation, resulting in their improved short-circuit current density and fill factor, simultaneously. In comparsion with as-cast devices, SA-T5-treated devices showed significantly improved power conversion efficiencies (PCEs) of 18.8 % for PM6:L8-BO, 17.8 % for PM6:DL8, and 17.6 % for PM6:PY-DT, respectively. Furthermore, the potential of SA-T5 in obtaining high-performance ternary OSCs was also confirmed, for example, a 18.1 % efficiency was realized in PM6:DL8:L8-BO based device. To our knowledge, the performance of these SA-T5-treated devices reaches the best results of different acceptor-based OSCs. Importantly, this work provides a rare and successful case to develop versatile SAs for high-performance OSCs.

Tetracyclic aromatic lactam-substituted tin-free donors for high-efficiency ternary organic solar cells via regulation of pre-aggregation and crystallization kinetics

Organic solar cells (OSCs) are rapidly developed for next-generation photovoltaic technologies due to low-cost and solution-processability etc. However, so far high-efficiency organic photovoltaic materials are typically prepared by multi-step Stille reactions, which are neither cost-efficient nor atom-economic, even raise safety concerns and incompatible with large-scale process. Large-scale industrial production of photovoltaic materials through simple, cost-effective, and green chemistry remains to be addressed. In this work, we present a case where two isomeric small-molecule donors based on polycyclic aromatic lactams (PAL) unit, named oPh2F and pPh2F with wide-bandgap and high-crystallinity, were designed and synthesized by atom-economic direct C-H activation strategy, modulates pre-aggregation and crystallization kinetics of host system PM6:Y6, induce distinct morphology evolution and effectively boost photovoltaic performance. The best power conversion efficiency (PCE) of 18.40 % for pPh2F-based ternary devices are found to be a fruit of improved light-harvesting ability, favorable vertical phase separation with enhanced crystallinity, the separated crystallization process of host materials and the higher and more balanced charge transport. To our knowledge, this study achieved the highest PCE among PM6:Y6-based ternary OSCs containing tin-free small-molecule donor, which not only highlights the great potential of PAL-based photovoltaic materials, but also promotes the integration of renewable energy with green chemistry.

Self-Assembled Molecules with Asymmetric Backbone for Highly Stable Binary Organic Solar Cells with 19.7 % Efficiency.

The hole-transporting material (HTM), poly (3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT : PSS), is the most widely used material in the realization of high-efficiency organic solar cells (OSCs). However, the stability of PEDOT : PSS-based OSCs is quite poor, arising from its strong acidity and hygroscopicity. In addition, PEDOT : PSS has an absorption in the infrared region and high highest occupied molecular orbital (HOMO) energy level, thus limiting the enhancement of short-circuit current density (Jsc) and open-circuit voltage (Voc), respectively. Herein, two asymmetric self-assembled molecules (SAMs), namely BrCz and BrBACz, were designed and synthesized as HTM in binary OSCs based on the well-known system of PM6 : Y6, PM6 : eC9, PM6 : L8-BO, and D18 : eC9. Compared with BrCz, BrBACz shows larger dipole moment, deeper work function and lower surface energy. Moreover, BrBACz not only enhances photon harvesting in the active layer, but also minimizes voltage losses as well as improves interface charge extraction/ transport. Consequently, the PM6 : eC9-based binary OSC using BrBACz as HTM exhibits a champion efficiency of 19.70 % with a remarkable Jsc of 29.20 mA cm-2 and a Voc of 0.856 V, which is a record efficiency for binary OSCs so far. In addition, the unencapsulated device maintains 95.0 % of its original efficiency after 1,000 hours of storage at air ambient, indicating excellent long-term stability.

Decreasing exciton dissociation rates for reduced voltage losses in organic solar cells

Enhancing the device electroluminescence quantum efficiency (EQEEL) is a critical factor in mitigating non-radiative voltage losses (VNR) and further improving the performance of organic solar cells (OSCs). While the common understanding attributes EQEEL in OSCs to the dynamics of charge transfer (CT) states, persistent efforts to manipulate these decay dynamics have yielded limited results, with the EQEEL of high-efficiency OSCs typically remaining below 10−2%. This value is considerably lower than that observed in high efficiency inorganic photovoltaic devices. Here, we report that EQEEL is also influenced by the dissociation rate constant of singlet states (kDS). Importantly, in contrast to the traditional belief that advocates maximizing kDS for superior photovoltaic quantum efficiency (EQEPV), a controlled reduction in kDS is shown to enhance EQEEL without compromising EQEPV. Consequently, a promising experimental approach to address the VNR challenge is proposed, resulting in a significant improvement in the performance of OSCs.

Zirconium Oxide Doped Organosilica Nanodots as Light- and Charge-Management Cathode Interlayer for Highly Efficient and Stable Inverted Organic Solar Cells.

In this work, it is reported that zirconium oxide (ZrO2) doped organosilica nanodots (OSiNDs: ZrO2) with light- and charge-management properties serve as efficient cathode interlayers for high-efficiency inverted organic solar cells (i-OSCs). ZrO2 doping effectively improves the light harvesting of the active layer, the physical contact between the active layer, as well as the electron collection property by habiting charge recombination loss. Consequently, all devices utilizing the OSiNDs: ZrO2 cathode interlayer exhibit enhanced power conversion efficiency (PCE). Specifically, i-OSCs based on PM6:Y6 and PM6:BTP-eC9 achieve remarkable PCEs of 17.16% and 18.43%, respectively. Furthermore, the PCE of device based on PM6:Y6 maintains over 97.2% of its original value following AM 1.5G illumination (including UV light) at 100mWcm-2 for 600min.

Theoretical investigation of substituted end groups in thiophene‐phenyl‐thiophene (TPT) derivatives for high efficiency organic solar cells

AbstractThe field of organic solar cells has witnessed notable advancements in the past few years, mostly due to the development of novel materials for the active layer. The current investigations reveal the potential of nine previously unexplored molecules (TP1–TP9) designed by end group modification of TPT4F molecule. These molecules were investigated at MPW1PW91/6‐31G (d, p) with DFT and TD‐DFT approach to study the various photovoltaic and geometrical parameters. The results obtained through computations indicated improvement in the investigated parameters. The terminal group modification shifted the absorption maximum towards longer wavelength in the UV‐visible region. Highly conjugated modified acceptors reduced the band gap. The lower excitation energies increased the rate of charge transfer. The designed molecules showed improved excited state lifetime in comparison to the reference. The open circuit voltage was determined using the PTB7 polymer, which exhibited a noticeable improvement, especially in TP1 (1.70 eV), TP3 (1.75 eV), TP4 (1.68 eV), TP6 (1.85 eV), and TP7 (1.75 eV) when compared with reference (1.59 eV). Moreover, charge transfer investigations of designed molecules with PTB7 complex were performed by analyzing the concentration of charge transfer over molecular orbitals, that is, HOMO to LUMO. All of the preceding investigations targeted to achieve high‐efficiency organic cells reveal that the altered molecules can be considered effective candidates to tackle future energy problems.

A New Nonfullerene Acceptor with Suppressed Energy Disorder for High-Efficiency Organic Solar Cells

A New Nonfullerene Acceptor with Suppressed Energy Disorder for High-Efficiency Organic Solar Cells

Dissociation of singlet excitons dominates photocurrent improvement in high-efficiency non-fullerene organic solar cells

Dissociation of singlet excitons dominates photocurrent improvement in high-efficiency non-fullerene organic solar cells

Research progress and application of high efficiency organic solar cells based on benzodithiophene donor materials

AbstractIn recent decades, the demand for clean and renewable energy has grown increasingly urgent due to the irreversible alteration of the global climate change. As a result, organic solar cells (OSCs) have emerged as a promising alternative to address this issue. In this review, we summarize the recent progress in the molecular design strategies of benzodithiophene (BDT)‐based polymer and small molecule donor materials since their birth, focusing on the development of main‐chain engineering, side‐chain engineering and other unique molecular design paths. Up to now, the state‐of‐the‐art power conversion efficiency (PCE) of binary OSCs prepared by BDT‐based donor materials has approached 20%. This work discusses the potential relationship between the molecular changes of donor materials and photoelectric performance in corresponding OSC devices in detail, thereby presenting a rational molecular design guidance for stable and efficient donor materials in future.

Simple-Structured Acceptor with Highly Interconnected Electron-Transport Pathway Enables High-Efficiency Organic Solar Cells.

Achieving desirable charge-transport highway is of vital importance for high-performance organic solar cells (OSCs). Here, it is shown how molecular packing arrangements can be regulated via tuning the alkyl-chain topology, thus resulting in a 3D network stacking and highly interconnected pathway for electron transport in a simple-structured nonfused-ring electron acceptor (NFREA) with branched alkyl side-chains. As a result, a record-breaking power conversion efficiency of 17.38% (certificated 16.59%) is achieved for NFREA-based devices, thus providing an opportunity for constructing low-cost and high-efficiency OSCs.

Morphological Homogeneity and Interface Modification as Determinant Factors of the Efficiency and Stability for Upscaling Organic Solar Cell.

Morphological homogeneity and interfacial traps are essential issues to achieve high-efficiency and stable large-area organic solar cells (OSCs). Herein, by the investigation of three quinoxaline-based acceptors, i.e., PM6:Qx-1, PM6:Qx-2, and PM6:Qx-p-4Cl, the performance degradation in up-scaling OSCs is explored. The inhomogeneous morphology in PM6:Qx-2 induces a nonuniform spatial distribution of charge generation, showing a rapid decline in efficiency and stability in large-area OSCs. In comparison, the homogeneous morphology in PM6:Qx-1 and PM6:Qx-p-4Cl alleviates the stability drop. When utilizing 2-phenylethylmercaptan to fill the interfacial traps, the stability drop disappears for PM6:Qx-1 and PM6:Qx-p-4Cl, while it persists for PM6:Qx-2. The PM6:Qx-1 large-are device yields a high efficiency of 13.47% and superior thermal stability (T80 = 2888h). Consequently, the interface modification dominates the performance degradation of large-area devices with homogeneous morphology, while it cannot eliminate the traps in inhomogeneous film. These results provide a clear understanding of degradation mechanisms in upscaling devices.

Isomerization of Benzothiadiazole Yields a Promising Polymer Donor and Organic Solar Cells with Efficiency of 19.0.

The exploration of high-performance and low-cost wide-bandgap polymer donors remains critical to achieve high-efficiency nonfullerene organic solar cells (OSCs) beyond current thresholds. Herein, the 1,2,3-benzothiadiazole (iBT), which is an isomer of 2,1,3-benzothiadiazole (BT), is used to design wide-bandgap polymer donor PiBT. The PiBT-based solar cells reach efficiency of 19.0%, which is one of the highest efficiencies in binary OSCs. Systemic studies show that isomerization of BT to iBT can finely regulate the polymers' photoelectric properties including i) increasing the extinction coefficient and photon harvest, ii) downshifting the highest occupied molecular orbital energy levels, iii) improving the coplanarity of polymer backbones, iv) offering good thermodynamic miscibility with acceptors. Consequently, the PiBT:Y6 bulk heterojunction (BHJ) device simultaneously reaches advantageous nanoscale morphology, efficient exciton generation and dissociation, fast charge transportation, and suppressed charge recombination, leading to larger VOC of 0.87V, higher JSC of 28.2 mA cm-2, greater fill factor of 77.3%, and thus higher efficiency of 19.0%, while the analog-PBT-based OSCs reach efficiency of only 12.9%. Moreover, the key intermediate iBT can be easily afforded from industry chemicals via two-step procedure. Overall, this contribution highlights that iBT is a promising motif for designing high-performance polymer donors.

Cyanoesterthiophene Based Low‐Cost Polymer Donors for High Efficiency Organic Solar Cells

AbstractTo achieve commercial application of organic solar cells (OSCs), it is necessary to reduce material costs and improve device efficiency. This paper reports on the utilization of a multifunctional building block, namely 3‐cyanoesterthiophene, which exhibits simple structure and accessibility of synthetic for cost‐effective and high‐performance polymer donors (PDs). Meanwhile, ternary and terpolymerization strategies have been studied. Two similar PDs, PBTCl0‐TCA and PBTCl100‐TCA, are synthesized, and the devices exhibit less‐than‐satisfactory efficiency of 13.21% and 11.53% due to mismatching energy level and imperfect morphology. The two PDs with comparable structures and commendable compatibility easily form alloy‐like phase in active layer, which can effectively boost the efficiency of ternary devices to 14.17% with retained high JSC and significant improved open‐circuit voltage (VOC) and fill factor (FF). Encouraged by the ternary blending phenomenon, a polymer donor (PBTCl50‐TCA) with same ratio by random terpolymerization is designed. And over 17% efficiency binary OSCs using terpolymerization donor are demonstrated. The synergies of incorporation of the cyanoester‐group and terpolymer endow the developed PDs with deep‐lying energy levels, face‐on orientation, thermodynamic miscibility with the prevailing nonfullerene acceptor and appropriate polymer crystallinity. The findings study provide valuable insights and support for the advancement of cost‐effective and high‐performance PDs.

A high-efficiency and stable organic solar cell with balanced crystallization kinetics

In this work, we present a conceptual strategy based on multi-acceptor components to realize balanced crystallization kinetics in organic solar cells (OSC) that deliver a 19.35% power conversion efficiency with superior photostability.