Fabrication Of Organic Solar Cells Research Articles

Enhancing Reproducibility in Organic Solar Cell Fabrication via Static Sequential Deposition with Cross-Linked Polymer Donor and Nonfullerene Acceptor

Enhancing Reproducibility in Organic Solar Cell Fabrication via Static Sequential Deposition with Cross-Linked Polymer Donor and Nonfullerene Acceptor

Synergistic strategies to unveil the dual influence of additive and annealing treatment on the morphology of isatin-derived low bandgap small molecule donor in solution-processed organic solar cells

A novel organic small molecule, 5-(4-(diphenylamino)phenyl)-1-octylindoline-2,3-dione (TPI) containing an alkyl chain substituted electron accepting isatin (indoline-2,3-dione) and strong electron withdrawing N, N-diphenylaniline units have been synthesized through Suzuki coupling reaction. The molecular structure of TPI is confirmed by NMR, FT-IR, and Mass spectroscopy techniques. The TPI molecule exhibits a low band gap of approximately ∼ 2.03 eV which is also supported by the DFT results. The influence of additive and heat treatment on the electronic, morphological, and photovoltaic performance of organic solar cells was investigated meticulously. The TPI donor exhibits complementary light absorption with fullerene acceptor in combination with DIO and TA which efficiently absorb the photon in the 300–730 nm range. The TPI was later used as an electron donor material for the fabrication of organic solar cells. Remarkably, the morphology-dependent optimized TPI:PC71BM (1:3.0) exposed excellent power conversion efficiency (PCE) of about ∼ 5.56 % with enhanced VOC of ∼ 0.811 V, JSC of 11.81 mA cm−2 and FF of 55.3 % fabricated in addition with DIO and thermal annealing treatment. Most importantly, the unencapsulated devices maintained > 96 % of the initial PCE value after 240 h under ambient temperature. Our findings indicate that isatin-derived small molecules with simple architecture propose great potential for promising BHJ-OSCs material.

π-π Stacking Modulation via Polymer Adsorption for Elongated Exciton Diffusion in High-Efficiency Thick-Film Organic Solar Cells.

Developing efficient organic solar cells (OSCs) with thick active layers is crucial for roll-to-roll printing. However, thicker layers often result in lower efficiency. This study tackles this challenge using a polymer adsorption strategy combined with a layer-by-layer approach. Incorporating insulator polystyrene (PS) into the PM6:L8-BO system creates PM6+PS:L8-BO blends, effectively suppressing trap states and extending exciton diffusion length in the mixed donor domain. Adding insulating polymers with benzene rings to the donor enhances π-π stacking of donors, boosting intermolecular interactions and electron wave function overlap. This results in more orderly molecular stacking, longer exciton lifetimes, and higher diffusion lengths. The promoted long-range exciton diffusion leads to high power conversion efficiencies of 19.05% and 18.15% for PM6+PS:L8-BO blend films with 100 and 300nm thickness, respectively, as well as a respectable 16.00% for 500nm. These insights guide material selection for better exciton diffusion, and offer a method for thick-film OSC fabrication, promoting a prosperous future for practical OSC mass production.

Computational design of new polymers having low exciton binding energy for organic solar cells fabrication: Chemical generation and visualization

Conventional organic solar cell (OSC) fabrication, based on the hit and trial methodology, is quite laborious and lethargic, requiring extensive human workforce and instrumental resources. Recent advancements in machine learning (ML) approaches have revolutionized selection of the suitable active polymeric layer for OSC devices. Among numerous aspects impacting efficacy of the OSC fabrication, the lower exciton binding energy (Eb) was found one of the most crucial factors. The dataset containing Eb values was prepared from already documented literature on polymeric active layers of OSC devices. Various ML models were applied and tested to predict Eb values accurately, however, the random forest regressor model was proved to be the most efficient one. The ML analysis was further utilized to develop a new and novel chemical database that could be utilized as an active layer for the fabrication of OSCs. The synthetic accessibility (SA) score was also investigated to explore the relative ease by which a proposed polymeric material could be synthesized in practical lab. Interestingly, analysis of the top thirty generated polymeric materials exhibited extremely decent SA score, and remarkably lower Eb values; both properties are highly desirable for the fabrication of efficient OSCs. Further, we also applied deep learning approach to generate and screen new monomers with lower Eb and SA score. This effort reveals significance of the computational data-driven approaches for real-life applications. Our current contribution of the novel polymeric materials database having extremely low Eb values could be valuable for the fabrication of efficient OSC devices.

Solution-based electrical doping of organic photovoltaics with non-fullerene acceptors facilitated by solvent vapor pre-treatment

Solution-based electrical doping of organic semiconductors using 12-molybdophosphoric acid (PMA) hydrate has been shown to allow p-type doping of conjugated polymers over a limited depth from the surface, enabling the fabrication of organic solar cells with a simplified device architecture. However, the doping level of certain conjugated polymers using PMA was found to be limited by the polymer film volume. Here, we report a modified PMA doping technique based on film volume expansion that is applicable to device fabrication, leading to hole-collecting layer-free non-fullerene organic photovoltaic devices, which exhibit a comparable photovoltaic performance to those with a commonly evaporated MoO3 hole-collecting layer.

Water-based layer-by-layer processing enables 19% efficient binary organic solar cells with minimized thickness sensitivity

A mesoporous layer was constructed by a donor-based nanoparticulate water-ink, which facilitates the infiltration of the acceptor, allowing the fabrication of efficient organic solar cells with a high thickness tolerance.

Industrial Kraft Lignin Based Binary Cathode Interface Layer Enables Enhanced Stability in High Efficiency Organic Solar Cells.

Herein, a binary cathode interface layer (CIL) strategy based on the industrial solvent fractionated LignoBoost kraft lignin (KL) is adopted for fabrication of organic solar cells (OSCs). The uniformly distributed phenol moieties in KL enable it to easily form hydrogen bonds with commonly used CIL materials, i.e., bathocuproine (BCP) and PFN-Br, resulting in binary CILs with tunable work function (WF). This work shows that the binary CILs work well in OSCs with large KL ratio compatibility, exhibiting equivalent or even higher efficiency to the traditional CILs in state of art OSCs. In addition, the combination of KL and BCP significantly enhanced OSC stability, owing to KL blocking the reaction between BCP and nonfullerene acceptors (NFAs). This work provides a simple and effective way to achieve high-efficient OSCs with better stability and sustainability by using wood-based materials.

Achieving efficient flexible and large-area organic solar cells via additive-assisted fluorous solvent soaking

Developing flexible and large-area organic solar cells (OSCs) is of vital importance for advancing the commercialization. However, using solvent additives during the film deposition is tricky and unpredictable for the large-area device. Furthermore, typical post-treatments like high-temperature thermal annealing might cause the undesired deformation of the flexible substrate, thus adversely affecting the photovoltaic performance. Herein, a new device engineering namely additive-assisted fluorous solvent soaking (AFSS), is developed as an alternative approach for OSCs fabrication. No solvent additive is used in the active layer deposition, providing more uniform films in large-area processing. The fresh-made film is subsequently soaked in a mixture of fluorous solvent and a tiny amount of solvent additive, wherein the cyclic movement of the fluorous solvent associated with the additive could facilitate the molecular reorganization at relatively low temperature (40 °C), and thus optimizing the morphology of the active layer. Compared with the traditional method, AFSS is more effective in various OSCs including the rigid or flexible substrates and the conventional or inverted device architectures. An ultra-flexible and large-area device fabricated by AFSS realizes a PCE of 12.63%. This work provides a robust and practical strategy to fabricate OSCs as well as other optoelectronic devices at low temperature.

Layer‐by‐Layer‐Processed Organic Solar Cells with 18.02% Efficiency Enabled by Regulating the Aggregation of Bottom Polymers

The fabrication of organic solar cells (OSCs) by a layer‐by‐layer (LBL) method has attracted growing attention in recent years. As already known, the pre‐aggregates of conjugated polymers in solution have a profound impact on their microstructure morphology in films. Herein, by simply controlling the solution temperature and annealing processes, the pre‐aggregation behavior of D18 polymer in solution can be fine‐tuned and the microstructure of D18 bottom layer is well manipulated. The optimized D18 bottom layer can effectively regulate L8‐BO upper‐layer‐forming suitable networks for efficient charge transportation. In addition, a vertical phase separation with a special D/D:A/A structure (P‐i‐N‐type component distribution) is also formed. As a result, compared to the 16.43% power conversion efficiency (PCE) of the bulk heterojunction devices, such control enables bilayer OSC devices based on the polymer D18 and L8‐BO to deliver an enhanced PCE of 18.02% with simultaneously improved short‐circuit current density, open‐circuit voltage, and fill factor. It is also demonstrated in these results that the LBL deposition process utilizing the pre‐aggregation of polymer and its fiber‐network‐forming ability is a very promising approach to improve charge dynamics, suppress carrier recombination, and fabricate highly efficient OSCs.

Effect of donor groups on the photovoltaic performance of benzothiadiazole-core substituted small molecules for fullerene-based bulk heterojunction organic solar cells

Herein, two symmetric donor-π-acceptor-π-donor-type π-conjugated small molecule donors (BTM and BTP), based on a benzothiadiazole central acceptor core unit and end-capped with electron-donating triphenylamine and 3,5-dimethoxyphenyl)vinyl, are synthesized via a multistep coupling reaction. The structural, thermal, optical, and electrochemical properties of the small molecules are systematically analyzed; subsequently, the molecules are applied as electron donor materials for bulk heterojunction organic solar cell fabrication. Compared with BTM, BTP exhibits a strong absorption spectrum with a precisely tuned optical bandgap (approximately 1.87 eV), desired morphology, and improved interfacial properties. The solar devices fabricated with BTP:PC71BM (1:2.5, w/w) exhibit a higher power conversion efficiency (PCE) of approximately 7.08% with an enhanced current density (JSC) of approximately 12.90 mA/cm2, high open-circuit voltage (VOC) of approximately 0.989 V, and fill factor (FF) of approximately 55.5% compared with BTM-based devices (approximately 4.86%). Notably, the high VOC achieved for the BTP:PC71BM (1:2.5, w/w) devices is a result of the deep-lying HOMO energy level and low LUMO energy offset (approximately 0.51 eV) between the BTP donor and PC71BM acceptor. The high hydrophobicity and stable surface morphology of BTP:PC71BM (1:2.5, w/w) exhibits a high room temperature stability approximately > 94% and retain 6.70% of PCE of its original PCE (7.08%) after 288 hr.

Effect of Steric Hindrance at the Anthracene Core on the Photovoltaic Performance of Simple Nonfused Ring Electron Acceptors

Solving the contradiction between good solubility and dense packing is a challenge in designing high-performance nonfullerene acceptors. Herein, two simple nonfused ring electron acceptors (o-AT-2Cl and m-AT-2Cl) carrying ortho- or meta-substituted hexyloxy side chains can be facilely synthesized in only three steps. The two ortho-substituted phenyl side chains in o-AT-2Cl cannot freely rotate due to a big steric hindrance, which endows the acceptor with good solubility. Moreover, o-AT-2Cl displays a more ordered packing than m-AT-2Cl as revealed by the absorption measurement. When blended with polymer donor D18 for the fabrication of organic solar cells (OSCs), o-AT-2Cl-based devices exhibit a favorable morphology, more efficient exciton dissociation, and better charge transport. Consequently, the optimal OSCs based on D18:o-AT-2Cl exhibit a power conversion efficiency (PCE) of 12.8%, which is significantly higher than the moderate PCE (7.66%) for D18:m-AT-2Cl-based devices. Remarkably, o-AT-2Cl shows a higher figure-of-merit value compared with classic high-efficiency fused ring electron acceptors. As a result, our research succeeds in obtaining nonfused ring acceptors with cost-effective photovoltaic performance and provides a valuable experience for simultaneously improving solubility as well as ensuring ordered packing of acceptors through regulating the steric hindrance via changing the position of substituents.

Highly Efficient Bilayer Polymer Solar Cells Using the Method of Sequential Processing with Additive Bilayer

Despite the research value of bilayer organic solar cells (OSCs) for commercialization in the future, the bulk‐heterojunction (BHJ) structure dominates the fabrication of OSCs because of its higher power conversion efficiency (PCE) compared with bilayer OSCs. Herein, four different types of bilayer OSC structures using sequential processing (SP) with an additive bilayer are investigated and considerably enhanced device performance is demonstrated. The performance of our bilayer devices based on a wide bandgap (PBDT‐DPPD‐TPD; P2) polymer and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) is improved from 2.88% for the conventional bilayer structure to 6.62%. More importantly, remarkable PCEs of 8.78% and 15.16% for PTB7‐Th/PCBM and PM6/Y6 bilayer OSCs, respectively, using the SP with additive bilayer method are achieved and the inhomogeneity issues of the BHJ structure are successfully addressed. Herein, a novel way to overcome the low efficiency of bilayer OSCs is suggested and an unprecedented possibility of renovation, breaking the standardization of OSC research, is presented.

A mesoscopic lattice model for morphology formation in ternary mixtures with evaporation

We develop a mesoscopic lattice model to study the morphology formation in interacting ternary mixtures with the evaporation of one component. As concrete potential application of our model, we wish to capture morphologies as they are typically arising during the fabrication of organic solar cells. In this context, we consider an evaporating solvent into which two other components are dissolved, as a model for a 2-component coating solution that is drying on a substrate. We propose a 3-spins dynamics to describe the evolution of the three interacting species. As main tool, we use a Monte Carlo Metropolis-based algorithm, with the possibility of varying the system’s temperature, mixture composition, interaction strengths, and evaporation kinetics. The main novelty is the structure of the mesoscopic model – a bi-dimensional lattice with periodic boundary conditions, divided into square cells to encode a mesoscopic range interaction among the units. We investigate the effect of the model parameters on the structure of the resulting morphologies. Finally, we compare the results obtained with the mesoscopic model with corresponding ones based on an analogous lattice model with a short range interaction among the units, i.e. when the mesoscopic length scale coincides with the microscopic length scale of the lattice.

Advances in layer-by-layer processing for efficient and reliable organic solar cells

This review presents the development of solution-processed layer-by-layer (LBL) deposition as a promising technique for the fabrication of organic solar cells using fullerene/fullerene-free acceptors.

Area-dependent performance variation of ultrasonic spray-coated organic solar cells

Here, a comparative study has been performed to understand the scalability of as developed ultrasonic spray deposition process for large-area organic solar cell fabrication. It was observed that the performance of the devices reduces with increasing active area dimensions. The short circuit current density and power conversion efficiency got decreased by more than 70% on increasing the device area from 0.04 to 1.5 cm2. In the case of small-area devices, the low electrical resistance owing to fewer droplet boundaries and negligible pinholes of the spray-coated film leads to better device performance. Whereas, upon scaling up the device area, the non-uniformity of the spray-coated film starts dominating and is found to be responsible for the reduction in overall device performance. The non-homogeneous film morphology in the case of larger-area devices greatly affects the charge generation, as it decreased from 4.77 × 1021 to 1.92 × 1021 cm−3 s−1 for large-area devices compared to small-area ones. The results suggest that the spray-deposited films greatly suffer from the limitation of droplet boundaries and pin-holes, which need to be addressed further with post-deposition treatments, in order to fabricate commercially viable large-area devices.

Volatile Additive Strategy Triggering 17.48% Efficient Post‐Treatment‐Free Organic Solar Cells

Active layer morphology is critical to determine the photovoltaic performance of organic solar cells (OSCs), and additive‐assisted morphology optimization is one of the most widely used strategies to fine tune the donor–acceptor network in the active layer. However, the postprocessing procedures and additive residues require additional efforts to maintain the device performance. Herein, a low‐cost, simple structural design and volatile solid additive 2,5‐diiodothiophene is demonstrated to effectively optimize the active layer morphology and prompt the photoelectric conversion efficiency (PCE) of OSCs without any post‐treatment, outperforming the devices fabricated with the prototypical volatile additive 1,4‐diiodobenzene. The 2,5‐diiodothiophene (DIT)‐optimized PM6:Y6 binary OSCs obtain a PCE of 17.48%, accompanied with reduced trap‐assisted charge recombination and balanced charge carrier mobility. In addition, we notice that the bromide and chlorine analogues of DIT can enhance the device performance to a certain extent as well. The findings suggest that the post‐treatment‐free nature of the thiophene‐based processing additives are promising candidates for tuning the active layer morphology, providing simple processability for large‐scale fabrication of OSCs.

Semi-transparent fullerene-based tandem solar cells with excellent light utilization efficiency enabled by careful selection of sub-cells

Semi-transparent (ST) tandem organic solar cells (OSCs) are typically exhibiting a trade-off between efficiency and average visible transmittance (AVT), which can be minimized by the appropriate selection of transparent contacts and absorbing materials in the sub-cells. Herein, we demonstrate efficient and highly transparent hetero-tandem OSCs constructed by stacking PBDT[2F]T:PC 71 BM and PCE10:PC 61 BM active layers as front-cell and back-cell, respectively. Optical and electrical simulations show that the PBDT[2F]T and PCE10-based sub-cells possess potential as ST and reflective tandem OSCs. With the aid of the simulations, we could fabricate reflective tandem OSCs with an efficiency of up to 8.3%. Furthermore, a ST tandem OSC, employing conductive silver nanowire top contact, achieved an AVT of 49.2%, efficiency of 5.3%, and high light utilization efficiency (LUE) of 2.61% under 1 sun, AM1.5G spectral illumination. This study demonstrates the importance of the sub-cells choices for developing ST tandem solar cells with a good balance of AVT and PCE, paving the way for solar windows of high performance. • Optical and electrical simulations performed to aid reflective and semi-transparent tandem OSCs fabrication. • Fabrication of tandem based on PBDT[2F]T:PC 71 BM and PCE10:PC 61 BM blends with PCE higher than their single-cells (8.2%). • Semi-transparent tandem device with a very high AVT of nearly 50%, in agreement with optical simulation. • The semi-transparent tandem based on PBDT[2F]T:PC 71 BM and PCE10:PC 61 BM blends achieved high PCE of 5.3% and LUE of 2.61%.

Ethanol‐Processable Polyfuran Derivative for Eco‐Friendly Fabrication of Organic Solar Cells Featuring Self‐Healing Function

Eco‐friendly fabrication of organic solar cells (OSCs) via alcohol or water is highly desired for their cost‐effective feature and benign profit for derived operators and ambient environment. Herein, a simple polyfuran derivative (PFO) that exhibits good solubility in ethanol/water solvent mixture is reported. Moreover, PFO displays broad optical absorption, high‐lying electronic energy level, and large hole mobility. The air‐ and ethanol‐processed PFO‐based OSCs deliver a fine efficiency of 2.25%. Even though only 45.24% of their initial efficiency is preserved for optimized devices after continuous illumination for 200 h in ambient atmosphere, the remained efficiency value of optimized devices can increase by 19.20% when undergoing intermittent illumination yet for the same light‐soaking time of 200 h. The self‐healing efficiency of devices suffering from discontinuous illumination is associated with the partial dissolution and reconstruction of hydrogen bonds in active layer. The results provide important guidelines for designing electroactive materials for safe and environmentally benign fabrication of OSCs with self‐sealing function.

Introduction of Water Treatment in Slot‐Die Coated Organic Solar Cells to Improve Device Performance and Stability

AbstractRecent advances in the development of organic solar cells (OSCs) have produced power conversion efficiency (PCE) of over 19%. Various studies have been conducted on scalable coating methods that are compatible with large‐area production of organic photovoltaic modules. However, it is still difficult to control the bulk heterojunction (BHJ) morphology of the active layer during large‐scale fabrication of OSCs. This study reports a morphology‐controllable strategy in OSCs using water treatment (WT) in the stirring process of the active solution, thus resulting in vortex agitation. The effects of WT and water injection volume are investigated based on three reference cells for the optimization of small‐ and large‐area devices, and the physicochemical and optical properties of the films are compared with those without WT. The thin films with WT exhibit a smoother morphology than those without WT, indicating well‐dispersed donor–acceptor phases. Therefore, enhanced efficiencies of the films are achieved via WT. Furthermore, large‐area solar cell modules with a total effective area of 10 cm2 are fabricated, and they exhibit superior PCEs as high as 11.92% (H‐NF‐DIW10), indicating that the WT method is a simple and effective strategy to fabricate large‐area organic photovoltaic modules.

Microfluidics: Continuous‐Flow Synthesis of Nanoparticle Dispersions for the Fabrication of Organic Solar Cells

AbstractState‐of‐the‐art solvents for the fabrication of organic solar cells are mostly toxic or hazardous. First attempts to deposit light‐harvesting layers from aqueous or alcoholic nanoparticle dispersions instead have been successful on laboratory scale, enabling future eco‐friendly production of organic solar cells. In this work, a scalable high‐throughput continuous‐flow microfluidic system is employed to synthesize surfactant‐free organic semiconductor dispersions by nanoprecipitation. By adjusting the differential speed of the syringe pumps, the concentration of the initial solute and the irradiation of the microfluidic chip, the synthesis can be controlled for tailored dispersion concentrations and nanoparticle sizes. The resulting dispersions are highly reproducible, and the semiconductor inks are stable for at least one year. The synthesis of the dispersions is exemplified on a polymer/fullerene combination with large‐scale availability.