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Dependency of Current Generated Upon Thermal Treatment Duration in Non-fullerene Organic Solar Cells
Abstract
In the present work, inverted organic solar cells (OSCs) based on the donor polymer PM6: non-fullerene acceptor-NFA Y7 were fabricated with architecture of ITO/ZnO/PM6:Y7/V2O5/Ag. We investigated the effect of chloronapthelene (CN) and diiodo octane (DIO) solvents additive along with thermal annealing duration on the performance of the fabricated NF-OSCs. We found that, as the annealing duration of the active blend increased, the performance of the fabricated devices enhanced. Furthermore, the obtained results showed that a significant improvement was obtained for the treated devices at 100 ℃ for 60 min, using 2 % CN additives which achieved an efficiency of 13.62 %. Where the power conversion efficiency (PCE) and the generated current density (JSC) were enhanced by 2 % and 12 %, respectively for the treated devices at 30 min, while the PCE and JSC were further enhanced by 10 % and 16 %, respectively for the same mentioned devices that thermally annealed for 60 min.
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Fine-tuning of blend morphology is a key factor that limits the performance of the bulk-heterojunction organic photovoltaics (BHJ-OPVs). Here, morphological control of the binary (PM6:Y7) and ternary (PM6:Y7:PC70BM) blends was performed through 1-chloronaphthalene (CN) solvent additives and thermal annealing treatment (TA) with respect to their influence on the photovoltaic performance. Moreover, a distinct study was accomplished on the optical and electronic properties of the treated and non-treated binary and ternary devices by external quantum efficiency measurements and impedance spectroscopy. The results indicated that these treatments affect the performance of the binary and ternary OPVs differently. Regarding the 2 % CN addition, the current density of the binary devices was improved by ≈ 27 %, while the fill factor of ternary devices showed pronounced increment of ≈ 22 %. A contradictory behavior was exhibited by TA for the binary and ternary OPVs. In which it improves the PCEs for binary devices (with/without CN) and 2 % CN treated ternary ones, while diminishing the PCEs of the ternary ones with 0 % CN. Accordingly, the highest efficiencies of the binary and ternary OPVs were obtained due to the dual effect of 2 % CN solvent additives along with the TA treatments.
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In organic solar cells (OSCs), cathode interfacial materials are generally designed with highly polar groups to increase the capability of lowering the work function of cathode. However, the strong polar group could result in a high surface energy and poor physical contact at the active layer surface, posing a challenge for interlayer engineering to address the trade-off between device stability and efficiency. Herein, we report a hydrogen-bonding interfacial material, aliphatic amine-functionalized perylene-diimide (PDINN), which simultaneously down-shifts the work function of the air stable cathodes (silver and copper), and maintains good interfacial contact with the active layer. The OSCs based on PDINN engineered silver-cathode demonstrate a high power conversion efficiency of 17.23% (certified value 16.77% by NREL) and high stability. Our results indicate that PDINN is an effective cathode interfacial material and interlayer engineering via suitable intermolecular interactions is a feasible approach to improve device performance of OSCs. It is desired to design cathode interfacial layers to simultaneously improve the efficiency and stability of organic solar cells and tune the cathode properties. Here, Yao et al. develop such interfacial layers for the best donor-acceptor system and achieve a high certified efficiency close to 17%.
Organic solar cell (OSC) is one of the most promising low‐carbon technologies for generation of electricity. It is blessed with relatively lower installation time and cost, light weight, semitransparent nature and suitability for roll‐to‐roll printing process. In the past, critics of OSC were concerned about its limited efficiency compared to other contemporary photovoltaic (PV) technologies. However, in the past few years, researchers in this field have made sufficient progress in terms of high performance and we have seen a boom in the OSC efficiency. Today, large number of OSCs are demonstrating >10% efficiency, recently reaching the milestone of 17%. The boost in efficiency is crucial for successful commercialization of OSC. In this review, we focus on the recent advancements of OSC to analyze the key players working behind the surge in its efficiency. We review the contribution of novel OPV materials and their morphology as well as novel device architectures. At the end, we also address the major challenges facing the upscaling and commercialization of OSCs. This article is protected by copyright. All rights reserved.
Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency. Halogenation has proved an effective strategy to improve the power conversion efficiencies of organic solar cells but it usually leads to lower open-circuit voltages. Here, Cui et al. unexpectedly obtain higher open-circuit voltages and achieve a record high PCE of 16.5% by chlorination.
The emerging dye-sensitized solar cells, perovskite solar cells, and organic solar cells have been regarded as promising photovoltaic technologies. The device structures and components of these solar cells are imperative to the device’s efficiency and stability. Polymers can be used to adjust the device components and structures of these solar cells purposefully, due to their diversified properties. In dye-sensitized solar cells, polymers can be used as flexible substrates, pore- and film-forming agents of photoanode films, platinum-free counter electrodes, and the frameworks of quasi-solid-state electrolytes. In perovskite solar cells, polymers can be used as the additives to adjust the nucleation and crystallization processes in perovskite films. The polymers can also be used as hole transfer materials, electron transfer materials, and interface layer to enhance the carrier separation efficiency and reduce the recombination. In organic solar cells, polymers are often used as donor layers, buffer layers, and other polymer-based micro/nanostructures in binary or ternary devices to influence device performances. The current achievements about the applications of polymers in solar cells are reviewed and analyzed. In addition, the benefits of polymers for solar cells, the challenges for practical application, and possible solutions are also assessed.
In this paper, we demonstrate that zinc oxide (ZnO) layers deposited by inkjet printing (IJP) can be successfully applied to the low-temperature fabrication of efficient inverted polymer solar cells (i-PSCs). The effects of ZnO layers deposited by IJP as electron transport layer (ETL) on the performance of i-PSCs based on PTB7-Th:PC70BM active layers are investigated. The morphology of the ZnO-IJP layers was analysed by AFM, and compared to that of ZnO layers deposited by different techniques. The study shows that the morphology of the ZnO underlayer has a dramatic effect on the band structure and non-geminate recombination kinetics of the active layer deposited on top of it. Charge carrier and transient photovoltage measurements show that non-geminate recombination is governed by deep trap states in devices made from ZnO-IJP while trapping is less significant for other types of ZnO. The power conversion efficiency of the devices made from ZnO-IJP is mostly limited by their slightly lower JSC, resulting from non-optimum photon conversion efficiency in the visible part of the solar spectrum. Despite these minor limitations their J–V characteristics compare very favourably with that of devices made from ZnO layer deposited using different techniques.
A new polymer donor (PBDB-T-SF) and a new small molecule acceptor (IT-4F) for fullerene-free organic solar cells (OSCs) were designed and synthesized. The influences of fluorination on the absorption spectra, molecular energy levels and charge mobilities of the donor and acceptor were systematically studied. The PBDB-T-SF:IT-4F-based OSC device showed a record high efficiency of 13.1%, and an efficiency of over 12% can be obtained with a thickness of 100–200 nm, suggesting the promise of fullerene-free OSCs in practical applications.
Early Separation
In photovoltaic devices, electrons excited by the absorption of light must travel across a junction, while the positively charged “holes” they leave behind effectively migrate in the opposite direction. If the electrons and holes do not separate efficiently, they can recombine and fail to produce any appreciable current. Gélinas et al. (p. 512 , published online 12 December; see the Perspective by Bredas ) studied this separation process by ultrafast optical absorption spectroscopy in thiophene-derived donor-fullerene acceptor systems common in organic photovoltaics and report a rate significantly faster than simple charge diffusion would suggest. The results implicate a coherent charge delocalization process, likely to involve fullerene π-electron states.
The increase in energy production costs for fossil fuels has led to a search for an economically viable alternative energy source. One alternative energy source of particular interest is solar energy. A promising alternative to inorganic materials is organic semiconductor polymer solar cells due to their advantages of being cheaper, light weight, flexible and made into large areas by roll-to-roll processing. However, the conventional architecture that is typically used for fabricating solar cells requires high vacuum to deposit the top metal electrode which is not suitable for roll-to-roll processing. Recently an inverted device architecture has been investigated as a suitable architecture for developing the ideal roll-to-roll type processing of polymer-based solar cells. This review will go over the recent advances and approaches in the development of this type of inverted device architecture. We will highlight some of the work that we have done to integrate materials, device, interface, and processing of the inverted device architecture platform to produce more idealized polymer-based solar cells.
Recent progress in the development of polymer solar cells has improved
power-conversion efficiencies from 3% to almost 9%. Based on
semiconducting polymers, these solar cells are fabricated from
solution-processing techniques and have unique prospects for achieving
low-cost solar energy harvesting, owing to their material and
manufacturing advantages. The potential applications of polymer solar
cells are broad, ranging from flexible solar modules and semitransparent
solar cells in windows, to building applications and even photon
recycling in liquid-crystal displays. This Review covers the scientific
origins and basic properties of polymer solar cell technology, material
requirements and device operation mechanisms, while also providing a
synopsis of major achievements in the field over the past few years.
Potential future developments and the applications of this technology
are also briefly discussed.
Nowadays, organic solar cells (OSCs) with Y6 and its derivatives as electron acceptors provide the highest efficiencies among the studied binary OSCs. To further improve the performances of OSCs, fabrication of ternary OSCs (TOSCs) is a convenient strategy. Essentially, morphology control and the trade-off between voltage and photocurrent are main critical issues in TOSCs. Herein, we address these problems by constructing TOSCs where an alloy-like composite is formed between Y6 and a newly designed derivative, BTP-M. Employing the electron-pushing methyl substituent in replacement of electron-withdrawing F atoms on Y6, BTP-M shows higher energy levels and lower crystallinity than Y6. As a result, the obtained Y6:BTP-M alloy can simultaneously optimize energy levels to reduce energy loss as well as morphologies of the active layers to favor photocurrent generation, leading to an enhanced open-circuit voltage (Voc) of 0.875 V together with a larger short-circuit current density (Jsc) of 26.56 mA cm-2 for the TOSCs based on polymer donor PM6 and Y6:BTP-M acceptor alloy. Consequently, a best efficiency of 17.03% is achieved for the corresponding TOSCs, which is among the best values for single-junction OSCs. In addition, our TOSCs also exhibit good thickness tolerance, and can reach a 14.23% efficiency even though the active layer is as thick as 300 nm.
Non-fullerene acceptors based organic photovoltaics (OPVs) have attracted considerable attention in the last decade due to their great potential to realize high-power conversion efficiencies. To achieve higher performance OPVs, the fundamental challenges are in enabling efficient charge separation/transport and a low voltage loss at the same time. Here, we have designed and synthesized a new class of non-fullerene acceptor, Y6, that employs an electron-deficient-core-based central fused ring with a benzothiadiazole core, to match with commercially available polymer PM6. By this strategy, the Y6-based solar cell delivers a high-power conversion efficiency of 15.7% with both conventional and inverted architecture. By this research, we provide new insights into employing the electron-deficient-core-based central fused ring when designing new non-fullerene acceptors to realize improved photovoltaic performance in OPVs.
Advances in organic photovoltaic technology for improving the power conversion efficiency (PCE) towards the theoretical maximum require efficient light-absorbing polymers, a high alignment-level of selective contacts, and an easy manufacturing process with low cost to reach them. The halide salts constitute a highly promising class of materials that can produce better selective contacts in solar cells for improving the PCE. In this article, we demonstrate and report the use of a haloid salt in organic solar cells utilized as an interlayer. The haloid salt is deposited on top or below of polyfluorene polymer (PFN) layer and after it is placed on a transparent conductive oxide (TCO). Thermal evaporation of LiF layers is carried out to deposit ultrathin films of 0.5 nm to 0.8 nm thickness. As a photoactive layer we use the low-bandgap PBDTTT-EFT:PC70BM bulk-heterojunction. Among the different architectures analyzed we obtained a PCE of 11.00%, with an outstanding fill factor of FF = 73.5%, which is among the best reported for solar cells. This new stacking of a halide salt with polyfluorene materials could find use in fully exploiting the potential of various halide systems, and also opens up new opportunities to improve OSCs with a view to achieving record efficiencies.
Organic solar cells (OSCs) have been dominated by donor:acceptor blends based on fullerene acceptors for over two decades. This situation has changed recently, with non-fullerene (NF) OSCs developing very quickly. The power conversion efficiencies of NF OSCs have now reached a value of over 13%, which is higher than the best fullerene-based OSCs. NF acceptors show great tunability in absorption spectra and electron energy levels, providing a wide range of new opportunities. The coexistence of low voltage losses and high current generation indicates that new regimes of device physics and photophysics are reached in these systems. This Review highlights these opportunities made possible by NF acceptors, and also discuss the challenges facing the development of NF OSCs for practical applications.
Organic, dye-sensitized and perovskite solar cell technologies have triggered widespread interest in recent years due to their very promising potential towards a high solar electricity future. A number of important milestones have marked the roadmap of each sector on the way to today's outstanding performances, but there still remains plenty of scope for further improvement. The most influential landmarks, together with basic concepts and future perspectives, are unraveled in this review. This journal is
The performance of organic compounds such as linear conjugated phenylene polymers, oligomers, rylene dye molecules, and multichromophores, in organic solar cells, are discussed. It is found that in the one-dimensional conjugated polyphenes, copolymers containing carbazole show a new record power conversion efficiency of 6% under AM 1.5 sunlight irradiation. Introducing donor-acceptor groups at the ends of the oligophenylene results in compounds well-suited for dye-sensitized solar cells. Using phenylenevinylene as a π-spacer and functionalizing this with triphenyl amine and cyano acetic acid, benzene-based materials as sensitizers achieve power conversion efficiencies of up to 8% in dye-sensitized solar cells (DSC). Ryene compounds, functionalized with electron-withdrawing groups such as imides, show photostability, thermostability, and chemical stability as well as high electron affinity.