Efficient Organic Photovoltaic Cells Research Articles

Highly Efficient and Stable Organic Photovoltaic Cells for Underwater Applications.

Organic photovoltaic (OPV) technology holds tremendous promise as a sustainable power source for underwater off-grid systems. However, research on underwater OPV cells is relatively scarce. Here, this gap is addressed by focusing on the exploration and development of OPV cells specifically designed for underwater applications. An acceptor, named ITO-4Cl, with excellent water resistance, is rationally designed and synthesized. Benefiting from its low energetic disorder and an absorption spectrum well-suited to the underwater environment, the ITO-4Cl-based OPV cell achieves an unprecedented power conversion efficiency (PCE) of over 25.6% at a water depth of 1m. Additionally, under 660nm laser irradiation, the cell demonstrates a notable PCE of 31.6%, indicating its potential for underwater wireless energy transfer. Due to the mitigation of thermal effects from solar irradiation, the lifetime of the ITO-4Cl-based OPV cell exceeds 7000h. Additionally, a flexible OPV cell is fabricated that maintains its initial PCE even under exposure to high pressures of 5MPa. A 32.5cm2 flexible module achieves an excellent PCE of 17%. This work fosters a deeper understanding of underwater OPV cells and highlights the promising prospects of OPV cells for underwater applications.

Molecular Design of Fully Nonfused Acceptors for Efficient Organic Photovoltaic Cells.

The nonfused thiophene-benzene-thiophene (TBT) unit offers advantages in obtaining low-cost organic photovoltaic (OPV) materials due to its simple structure. However, OPV cells, including TBT-based acceptors, exhibit significantly lower energy conversion efficiencies. Here, we introduce a novel approach involving the design and synthesis of three TBT-based acceptors by substituting different position-branched side chains on the TBT unit. In comparison to TBT-10 and TBT-11, TBT-13, which exclusively incorporates α-position branched side chains with a large steric hindrance, demonstrates a more planar and stable conformation. When blended with the donor PBQx-TF, TBT-13-based blend film achieves favorable π-π stacking and aggregation characteristics, resulting in excellent charge transfer performance in the corresponding device. Due to the simultaneous enhancements in short-circuit current density and fill factor, the TBT-13-based OPV cell obtains an outstanding efficiency of 16.1%, marking the highest value for the cells based on fully nonfused acceptors. Our work provides a practical molecular design strategy for high-performance and low-cost OPV materials.

Design and Synthesis of Dibenzothiadiazolopyrrolothiophene (DBTPT)‐Based Acceptors for Efficient Organic Photovoltaic Cells

AbstractThe central core in non‐fullerene acceptors (NFAs) plays a crucial role in determining the efficiency of organic photovoltaic (OPV) cells. To further advance the development of OPV cells, it is crucial to synthesize novel central cores for constructing high‐performance NFAs. Here, dibenzothiadiazolopyrrolothiophene (DBTPT) is introduced, a ladder‐type [1,2,5]thiadiazolo[3,4‐e]indole‐fused pentacyclic thiophene unit, into photovoltaic materials. By employing the DBTPT unit as the rigid molecular backbone and modifying the side chain of the thiophene π‐bridge, two new acceptor‐π‐acceptor’‐donor‐acceptor’‐π‐acceptor (A‐π‐A'DA’‐π‐A)‐type acceptors (T6 and T9) are synthesized. The effects of lateral alkyl and alkoxy side chains on the optoelectronic properties, charge transport, and molecular packing order are systematically investigated. When blended with polymer donor Poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b']dithiophene))‐alt‐(5,5‐(1',3'‐di‐2‐thienyl‐5'7'‐bis(2‐ethylhexyl)benzo[1',2'‐c:4',5'‐c']dithiophene‐4,8‐dione))] (PBDB‐T), the blend film based on T9 with alkoxy side chains shows favorable molecular stacking and phase separation, resulting in excellent charge transfer performance. Benefiting low energetic disorder, PBDB‐T:T9‐based cell achieves an efficiency of 12.6% with a markedly low energy loss of 0.568 eV. The preliminary results demonstrate that the DBTPT unit has great potential for the construction of novel NFAs for high‐performance OPV cells.

Iodinated Electron Acceptor with Significantly Extended Exciton Diffusion Length for Efficient Organic Photovoltaic Cells.

Iodination has unlocked new potentials in organic photovoltaics (OPVs). A newly designed and synthesized iodinated non-fullerene acceptor, BO-4I, showcases exceptional excitation delocalization property with the exciton diffusion length increased to 80 nm. The enhanced electron delocalization property is attributed to the larger atomic radius and electron orbit of the iodine atom, which facilitates the formation of intra-moiety excitations in the acceptor phase. This effectively circumvents the charge transfer state-related recombination mechanisms, leading to a substantial reduction in non-radiative energy loss (ΔEnr ). As a result, OPV cell based on PBDB-TF : BO-4I achieves an impressive efficiency of 18.9 % with a notable ΔEnr of 0.189 eV, markedly surpassing their fluorinated counterparts. This contribution highlights the pivotal role of iodination in reducing energy loss, thereby affirming its potential as a key strategy in the development of advanced next-generation OPV cells.

Iodinated Electron Acceptor with Significantly Extended Exciton Diffusion Length for Efficient Organic Photovoltaic Cells

AbstractIodination has unlocked new potentials in organic photovoltaics (OPVs). A newly designed and synthesized iodinated non‐fullerene acceptor, BO‐4I, showcases exceptional excitation delocalization property with the exciton diffusion length increased to 80 nm. The enhanced electron delocalization property is attributed to the larger atomic radius and electron orbit of the iodine atom, which facilitates the formation of intra‐moiety excitations in the acceptor phase. This effectively circumvents the charge transfer state‐related recombination mechanisms, leading to a substantial reduction in non‐radiative energy loss (ΔEnr). As a result, OPV cell based on PBDB‐TF : BO‐4I achieves an impressive efficiency of 18.9 % with a notable ΔEnr of 0.189 eV, markedly surpassing their fluorinated counterparts. This contribution highlights the pivotal role of iodination in reducing energy loss, thereby affirming its potential as a key strategy in the development of advanced next‐generation OPV cells.

Morphology Control for Efficient Nonfused Acceptor-Based Organic Photovoltaic Cells.

Non-fused electron acceptors have huge advantages in fabricating low-cost organic photovoltaic (OPV) cells. However, morphology control is a challenge as non-fused C─C single bonds bring more molecular conformations. Here, by selecting two typical polymer donors, PBDB-TF and PBQx-TF, the blend morphologies and its impacts on the power conversion efficiencies (PCEs) of non-fused acceptor-based OPV cells are studied. A selenium-containing non-fused acceptor named ASe-5 is designed. The results suggest that PBQx-TF has a lower miscibility with ASe-5 when compared with PBDB-TF. Additionally, the polymer networks may form earlier in the PBQx-TF:ASe-5 blend film due to stronger preaggregation performance, leading to a more obvious phase separation. The PBQx-TF:ASe-5 blend film shows faster charge transfer and suppressed charge recombination. As a result, the PBQx-TF:ASe-5-based device records a good PCE of 14.7% with a higher fill factor (FF) of 0.744, while the PBDB-TF:ASe-5-based device only obtains a moderate PCE of 12.3% with a relatively low FF of 0.662. The work demonstrates that the selection of donors plays a crucial role in controlling the blend morphology and thus improving the PCEs of non-fused acceptor-based OPV cells.

Molecular modifications in fluorene core for efficient organic photovoltaic cells

The upgraded version of solar cells is organic photovoltaic (OPV) device. Substantial efforts have been made in development of new light sensitive materials (donor, acceptors and hole transport materials etc.), and further modification in different units of these materials and device fabrication process to achieve better performance in OSCs. Fluorene is a fluorescent, poor electron providing polycyclic aromatic molecule shows absorption from 220 to 310 nm with λmax of 329 nm and deep lying HOMO energy level which is favorable to gain high value of open circuit voltage (Voc) of fluorene based materials. Several acceptor materials have been synthesized by using fluorene as a building block for solution processable organic photovoltaics (OPVs). A variety of climatic type fluorene based NFAs by placing different donor (D) and acceptor (A) units with a structural arrangement of A-D/A-D-D/A-A were explored for OPV cells. Further several modifications in molecular backbone of the acceptors were performed by modifying central donor such as fluorene, spiro fluorene and fluorene unit fused with other aromatic ring and by revamping at π-bridge, terminal units and alkyl side chain to enhance the power generation efficiency of solar cells. This review for the most part focuses on encapsulating the simple fluorene and its derivatives core based small molecule NFAs based.

Benzodithiophene-based Acceptor-Donor-Acceptor-type compounds for highly efficient organic photovoltaic cells

In this study, the structural, optical and electronic properties of a conjugated A-D-A compound based on indandione and benzobitiophene, which is widely used in the production of organic solar cells, were theoretically calculated using different functionals of the Density Functional Theory (DFT) method. For this purpose, different parameters such as frontier molecular orbital (FMO), which is called the highest occupied molecular orbital HOMO and the lowest unoccupied molecular orbital LUMO, energy gap Egap (HOMO-LUMO), the density of states (DOS), the absorption maximum λmax, excitation energy Eex and transition density matrix (TDM) were calculated. In addition, reduced density gradient (RDG) and open circuit voltages VOC were simulated to evaluate hole-electron localization. According to the results obtained from this study, the investigated compound exhibits significant visual absorption and interesting electron transport properties due to its hard-flat structures. The open circuit voltage (VOC) of compounds with BTPF acceptors is 1.45 V. This study has shown that BTPF compound has great potential for integration into solar cells as an electron donor material and has provided evidence that the investigated material may be a potential photovoltaic material candidate.

A Wide Bandgap Acceptor with Large Dielectric Constant and High Electrostatic Potential Values for Efficient Organic Photovoltaic Cells.

Low-bandgap materials have achieved rapid development and promoted the enhancement of power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. However, the design of wide-bandgap non-fullerene acceptors (WBG-NFAs), required by indoor applications and tandem cells, has been lagging far behind the development of OPV technologies. Here, we designed and synthesized two NFAs named ITCC-Cl and TIDC-Cl by finely optimizing ITCC. In contrast with ITCC and ITCC-Cl, TIDC-Cl can maintain a wider bandgap and a higher electrostatic potential simultaneously. When blending with the donor PB2, the highest dielectric constant is also obtained in TIDC-Cl-based films, enabling efficient charge generation. Therefore, the PB2:TIDC-Cl-based cell possessed a high PCE of 13.8% with an excellent fill factor (FF) of 78.2% under the air mass 1.5G (AM 1.5G) condition. Furthermore, an exciting PCE of 27.1% can be accomplished in the PB2:TIDC-Cl system under the illumination of 500 lux (2700 K light-emitting diode). Combined with the theoretical simulation, the tandem OPV cell based on TIDC-Cl was fabricated and exhibited an excellent PCE of 20.0%.

Preface

Green energy refers to energy that can be directly used in production and life. It includes nuclear energy and renewable energy. With the continuous growth of energy demand and the increasing awareness of environmental protection in the countries around the world, it is urgent and imperative to establish a green energy innovation research and development, promotion and application system, and electricity will play a huge role in the development of green energy.2023 2nd International Conference on Green Energy and Power Systems (ICGEPS 2023) was held virtually under such a background in Changsha, China on January 6th to 8th, 2023. The aim of the symposium was to provide an opportunity for international experts, academics, researchers, practitioners and students working in the areas of green energy and power system to exchange information on the R&D and commercialization of green energy and power system. New developments, concepts, future research trends and potential commercialization areas were also discussed.The topics covered in the proceedings of ICGEPS 2023 are as follows: Power Systems and Its Automation, Measurement Technology and Instrumentation, Sensors and Micro Machines, Clean Energy Technology, Sustainable Coal Utilization and Clean Coal Technology, etc. Approximately 100 experts and scholars from almost 10 countries participated in the conference. The conference featured keynote speeches, oral presentations, and poster presentations.During the keynote speech part, three well-known professors delivered expertise lectures by imparting the latest findings from their respective research domains. Among them, Prof. Chong Kok Keong from Universiti Tunku Abdul Rahman, Malaysia addressed a keynote speech on Performance Analyses of Photovoltaic Module under Different Spectral Irradiances by Considering both Photonic and Electrical Characteristics. The solar spectral irradiance varies significantly for different locations and time due to latitude, humidity, cosine effect of incident sunlight, etc. To predict the actual performance of photovoltaic module under local climate conditions, he and his team proposed a methodology to compute the power-conversion efficiency of organic photovoltaic cells based upon indoor measurement with a solar simulator, the measured local solar spectrum, and making use of both optical and electrical factors. It was a wonderful opportunity for all the participants to interact with the experts and specialists to get their advice or suggestions.We would like to express our gratitude to all the participants for their presentations and discussions, which made the conference very successful indeed. We are also grateful to the Conference Chair, the Program Committee Chair, the Publication Chair, the Organizing Committee, and the Technical Program Committees for their fruitful work. We would like to express our thanks to all the authors for their time and genuine efforts, and to the reviewers for their fruitful comments during the preparation of this volume.The Committee of ICGEPS 2023List of Committee Member is available in this pdf.

An Ortho-Bisalkyloxylated Benzene-Based Fully Non-fused Electron Acceptor for Efficient Organic Photovoltaic Cells.

To develop the low-cost nonfullerene acceptors (NFAs), two fully non-fused NFAs (TBT-2 and TBT-6) with ortho-bis((2-ethylhexyl)oxy)benzene unit and different side chains onto thiophene-bridges are synthesized through highly efficient synthetic procedures. Both acceptors show good planarity, low optical gaps (≈1.51eV), and deep highest occupied molecular orbital levels (≤-5.77eV). More importantly, the single-crystal structure of TBT-2 shows compact molecular arrangement due to the existence of intramolecular interactions between adjacent aromatic units and strong π-π stacking between intermolecular terminal groups. When the two acceptors are fabricated organic photovoltaic (OPV) cells by combining with a wide optical gap polymer donor, the TBT-6 with strong crystallization forms large domain sizes in bulk heterojunction (BHJ) blend. As a result, the TBT-6-based OPV cell shows a low power conversion efficiency (PCE) of 9.53%. In contrast, the TBT-2 with proper crystallization facilitates morphological optimization in the BHJ blend. Consequently, the TBT-2-based OPV cell gives an outstanding PCE of 13.25%, which is one of the best values among OPV cells with similar optical gaps. Overall, this work provides a practical molecular design strategy for developing high-performance and low-cost electron acceptors.

Short bandgap of porphyrin molecules (Py) filled in a semiconducting single-walled carbon nanotube (Py@NT17) for highly efficient organic photovoltaic cells

In this paper, the porphyrin (Py) molecule, which is filled in the semiconducting single-walled carbon nanotube (SWNT) known as CNT17, is investigated. We have calculated the optoelectronic characteristics of two configurations of the hybrid system with a single Py molecule filled into CNT17 (Py@CNT17 and Py2@CNT17) using density functional theory (DFT). According to the investigation’s findings, a charge transfer occurred between the Py molecules and the CNT17 nanotube, confirming the stability of the structure. As determined by the electronic calculation, we discovered that the rise in the fermi energy position of CNT17 after encapsulation, suggests a CT connection between Py and CNT17.

Selenium‐Based Nonfused Electron Acceptors for Efficient Organic Photovoltaic Cells

Selenium heterocycles are widely used in constructing organic semiconductors due to their advantages in narrowing the bandgap and enhancing the intermolecular packing. Herein, the application of Se substitution in designing nonfused electron acceptors (nfEAs) is studied. From a thiophene analog (A4T‐16), three nfEAs with two (ASe‐1 and ASe‐2) or four (ASe‐3) selenophene units are synthesized. The results suggest that the incorporation of Se atoms will downshift the lowest unoccupied molecular orbit level, upshift the highest occupied molecular orbit level, and exhibit redshifted absorption spectra due to the enhanced quinoidal character. The crystallographic data indicate that Se‐containing molecules exhibit more planar conjugate skeleton and thus lead to the improvement of carrier mobility. When blended with a polymer donor PBDB‐TF, ASe‐1‐, ASe‐2‐, and ASe‐3‐based organic photovoltaic (OPV) cells obtain power conversion efficiencies of 12.7%, 11.0%, and 10.4%, respectively. This work provides a comprehensive study of the application of Se substitution in designing low bandgap nfEAs for efficient OPV cells.

Non-Fullerene Acceptors Containing Alkylated Large π-Conjugated Building Blocks for Efficient Organic Photovoltaic Cells

Non-Fullerene Acceptors Containing Alkylated Large π-Conjugated Building Blocks for Efficient Organic Photovoltaic Cells

Achieving 31% efficiency in organic photovoltaic cells under indoor light using a low energetic disorder polymer donor

A series of wide bandgap terpolymers are designed and synthesized, which exhibit low energetic disorders. Based on the terpolymers, outstanding PCEs of over 31% (1000 lux) for an indoor OPV cell and over 18.2% (one-sun) for an OPV cell are achieved.

Low-cost and high-performance poly(thienylene vinylene) derivative donor for efficient versatile organic photovoltaic cells

The utilization of donor materials with complex structures obviously increases the costs of organic photovoltaic (OPV) cells. Therefore, low-cost and high-performance are two issues that must be considered when designing polymer donors for the preparations of large-area OPV cells. Here, a poly(thienylene vinylene) derivative, named PTVT-BT was reported. PTVT-BT has a very simple completely non-fused molecular structure. PTVT-BT shows planar molecular structure and obvious solution aggregation effect. Besides, PTVT-BT demonstrates a high hole mobility up to the magnitude of 10-2 cm-2 V-1 s-1. The external quantum efficiency of electroluminescence of PTVT-BT is 7 × 10-3. As a result, the OPV cell based on PTVT-BT:eC9 demonstrates a power conversion efficiency (PCE) of 16.31%, which is the highest value among the poly(thienylene vinylene)- and polythiophene-based OPV cells. The tandem OPV cell with PTVT-BT as the donor of the sub-cell yields an outstanding PCE of 18.49%. Besides, the indoor OPV cell based on PTVT-BT:BTA3 exhibits a PCE of 27.30% under a light-emitting diode (LED) illumination of 1000 lux (2700 K). This study indicates that PTV-derivative is a kind of promising material for the future OPV industrialization.

Design of ultranarrow-bandgap acceptors for efficient organic photovoltaic cells and highly sensitive organic photodetectors

The fabrication of multifunctional electronic devices based on the intriguing natures of organic semiconductors is crucial for organic electronics. Ultranarrow-bandgap materials are in urgent demand for fabricating high-performance organic photovoltaic (OPV) cells and highly sensitive near-infrared organic photodetectors (OPDs). By combining alkoxy modification and an asymmetric strategy, three narrow-bandgap electronic acceptors (BTP-4F, DO-4F, and QO-4F) were synthesized with finely tuned molecular electrostatic potential (ESP) distributions. Through the careful modulation of electronic configurations, the optical absorption onsets of DO-4F and QO-4F exceeded 1 μm. The experimental and theoretical results suggest that the small ESP of QO-4F is beneficial for achieving a low nonradiative voltage loss, while the large ESP of BTP-4F can help obtain high exciton dissociation efficiency. By contrast, the asymmetric acceptor DO-4F with a moderate ESP possesses balanced voltage loss and exciton dissociation, yielding the best power conversion efficiency of 13.6% in the OPV cells. OPDs were also fabricated based on the combination of PBDB-T:DO-4F, and the as-fabricated device outputs a high shot-noise-limited specific detectivity of 3.05 × 1013 Jones at 850 nm, which is a very good result for near-infrared OPDs. This work is anticipated to provide a rational way of designing high-performance ultranarrow-bandgap organic semiconductors by modulating the molecular ESP.

Enhancement Efficiency of Organic Photovoltaic Cells via Green Solvents and Nontoxic Halogen‐Free Additives

AbstractFor organic photovoltaic cells, the development of new green solvents and nontoxic and halogen‐free additives is an urgent issue. Here, a simple combination of o‐xylene (O‐XY) and ethyl 2‐hydroxybenzoate (EHB) is introduced in inverted devices based on poly[4,8‐bis(5‐(2‐ethylhexyl)‐thiophene‐2‐yl) benzo[1,2‐b;4,5‐b′] dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b] thiophene)‐2‐carboxylate‐2‐6‐diyl]:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PTB7‐Th:PC71BM) as blend layers, the device performance reaches optimal values (9.29%) when O‐XY and 3% EHB are introduced as additives, accompanied by the maximum fill factor (67.5%) and JSC (17.20 mA cm−2). From the results of characterization analysis, it is clear that EHB additive improves the crystallinity of the donor by regulating the kinetic process of active layer formation, selectively solubilizes the more aggregated fullerene acceptors, which allows PTB7‐Th to enter the conformational domain of PC71BM, and accelerates the molecular rearrangement. Besides, the EHB additive not only reduces the recombination, increases the carrier migration rate but also promotes the crystallinity of the donor, resulting in a tighter stacking. This work provides a green combination of solvents and additives that is important for the mass production of solar cells.

Naphthalenothiophene imide-based polymer exhibiting over 17% efficiency

Summary Developing novel electron-deficient monomers is crucially important for the future development of non-fullerene organic solar cells. Here, we report a new electron-deficient monomer naphthalenothiophene imide (NTI) and NTI-based copolymers PNTB and PNTB-2T. The strong electron-withdrawing ability of NTI could effectively lower the HOMO level of the polymer that facilitates the tuning of the polymer’s physical properties while simultaneously maintaining the low-lying HOMO value. Polymer chains modification by introducing extra thiophenes results in the closed π−π stacking and ordered polymer chain packing of PNTB-2T and is proven to be an effective strategy to increase the device performance. Thus, solar cell devices for PNTB-2T:Y6 exhibit an efficiency of 16.72%, which is further enhanced to 17.35% by the third component PC71BM, whereas that for PNTB:Y6 is only 3.81%. Importantly, PNTB-2T-based devices exhibit excellent batch-to-batch reproducibility. These features make this family of polymer donors very promising and the design strategies will enlighten future development of high-performance polymer donors for organic solar cells (OSC).

Ternary Organic Photovoltaic Cells Exhibiting 17.59% Efficiency with Two Compatible Y6 Derivations as Acceptor

Efficient organic photovoltaic cells (OPVs) are fabricated using two structurally similar Y6 derivations (BTP‐BO‐4F and Y6‐1O) as acceptor and PM6 as donor. The two binary OPVs exhibit a high fill factor (FF) (>76%), the complementary short‐circuit‐current density (JSC) and open‐circuit voltage (VOC). The high FFs of binary OPVs indicate the good compatibility of corresponding materials to form efficient charge transport channels. A power conversion efficiency (PCE) of 17.59% is obtained from ternary OPVs with 15 wt% Y6‐1O in acceptors, benefiting from the simultaneously improved JSC of 26.13 mA cm−2, a VOC of 0.860 V, and an FF of 78.26%. The values of VOC of ternary OPVs can be gradually increased along with the incorporation of Y6‐1O, suggesting the preferred formation of an alloyed state between BTP‐BO‐4F and Y6‐1O due to their good compatibility. Meanwhile, the cascaded energy levels of BTP‐BO‐4F and Y6‐1O can form efficient electron transport channels in ternary active layers. The main contribution of Y6‐1O can be summarized as enhancing photon harvesting, optimizing phase separation, and adjusting molecular arrangement. The experimental results may provide new insight on developing efficient ternary OPVs by selecting two well‐compatible acceptors.