OPV Cells Research Articles

Unveiling the Shadows: Overcoming Bottlenecks in Scaling Organic Photovoltaic Technology from Laboratory to Industry

AbstractOrganic photovoltaic (OPV) technology has recently achieved remarkable progress in academia, attaining power conversion efficiencies exceeding 19%, a breakthrough previously unimaginable. Despite these advancements, the translation of high‐efficiency OPV cells into the commercialization of OPV modules has been limited, impeding the market penetration of OPV technology. Upon careful examination, various challenges emerge, including disparities between laboratory research and industrial production in device architecture, influenced by considerations of cost and manufacturability. Additionally, the incorporation of high‐efficiency materials requires careful consideration not only of the compatibility between the photoactive layer and interface layers or transparent electrodes but also of the associated synthetic complexity of chemical structures and cost implications. While these issues are crucial, they may not be widely discussed in current mainstream research. In this article, the purpose is to identify bottlenecks from a material techniques perspective, with the aim of promoting increased resources in the research of pertinent module technologies. This effort is intended to propel OPV technology toward greater success and bring it into closer alignment with the goals of commercialization.

Toward Indoor Simulations of OPV Cells for Visible Light Communication and Energy Harvesting

Toward Indoor Simulations of OPV Cells for Visible Light Communication and Energy Harvesting

Low‐Cost Fully Non‐fused Ring Acceptor Enables Efficient Organic Photovoltaic Modules for Multi‐Scene Applications

AbstractOrganic photovoltaic (OPV) cells, with highly tunable light‐response ranges, offer significant potential for use in driving low‐power consumption off‐grid electronics in multi‐scenarios. However, development of photoactive layer materials that can meet simultaneously the requirements of diverse irradiation conditions is a still challenging task. Herein, a low‐cost fully non‐fused acceptor (denoted as GS60) featuring well‐matched absorption spectra with solar, scattered light and artificial light radiation was designed and synthesized. Systematic characterizations revealed that GS60 possessed outstanding photoelectron properties and ideal morphology, which resulted in reduced voltage loss and suppressed charge recombination. By blending with a non‐fused ring polymer PTVT−T, the as‐obtained GS60 based OPV cells achieved a good power conversion efficiency (PCE) of 14.1 %, a high value for the cells based on non‐fused ring bulk heterojunction. Besides, manufactured large‐area OPV modules based on PTVT−T:GS60 yielded PCEs of 11.2 %, 11.8 %, 12.1 %, 23.1 %, and 20.3 % under irradiation of AM 1.5G, natural light of cloudy weather, natural light in shadow, laser and indoor, respectively. The PTVT−T:GS60 devices exhibited considerable potential in terms of improving photostability and reducing material cost. Overall, this work provides novel insight into the molecular design of low‐cost non‐fused ring acceptors, and extended potential of medium band gap acceptors based OPV cells used in various application scenarios.

An Interfacial Material with Low Trap Density Enables Efficient Organic Photovoltaic Cells for Multi‐Scene Applications

AbstractOrganic photovoltaic (OPV) cells have great potential in multi‐scene applications because of their easily tunable optical absorption properties. However, the lagging development of the interlayer material limits the practicality of OPV cells. Herein, a naphthalene diimide‐based polymer cathode interlayer named PNDI‐Br is reported. The suitable energy level and improved light utilization enable the PNDI‐Br‐based cells to achieve a high power conversion efficiency of 18.7% under the illumination of AM 1.5G, representing the highest efficiency of inverted OPV cells. Under continuous illumination, PNDI‐Br‐based OPV cells can maintain an efficiency of over 80% after 1000 h, which reveals excellent stability of the cells. Furthermore, the decreased trap density and charge accumulation of PNDI‐Br‐based OPV cells results in limited charge recombination, which enables the cells to obtain a high fill factor and a low voltage loss in multi‐lighting conditions. This work provides a stimulus for multi‐scene applications of OPV 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.

Hammer throw-liked hybrid cyclic and alkyl chains: A new side chain engineering for over 18 % efficiency organic solar cells

Side chain engineering has been commonly recognized to be a simple and effective strategy in designing organic photovoltaic materials and increasing power conversion efficiencies. Different from recent traditional side chain modulation, this work presented the design and synthesis of a family of fresh hybrid side chain by combining the relatively rigid cyclic and flexible alkyl chain. To be specific, cyclopentane, cyclohexane and cycloheptane were introduced to the tail of the alkyl side chain, through which novel polymer donors D18-C6Cp, D18-C6Ch and D18-C6Chp were prepared based on the excellent skeleton of D18. In comparison with simplex cyclic or branched chain, hybrid side chains with preferential conformations were capable of impacting the self-assembling characteristics and facilitating the interpenetrating networks of blend films, thereby contributing to high-efficiency charge transport, lower energy loss, and inhibited charge recombination. Strikingly, the D18-C6Ch:L8-Bo-based single junction OPV cells reveal a prominent FF of 78.7 %, and a Voc of 0.91 V with the maximum PCE up to 18.2 %. This work exhibits an effective hybrid side chain engineering to synergistically tune the self-assembly properties and finally improve organic photovoltaic performance, which would be a broad potential in developing novel materials in the field of organic optoelectronics.

Scalable Fabrication of Flexible Large-area Inverted Organic Photovoltaic Cells

Scalable large-area inverted organic hotovoltaic (OPV) cells were fabricated on a flexible polyethylene naphthalate (PEN) substrate. To account for the scalability and impact of the substrate (rigid versus flexible), OPVs of various sizes (0.04-1.6 cm²) were fabricated on flexible PEN and rigid glass substrates. A single OPV cell area of up to 1.6 cm² can be fabricated using a solution process at a low temperature of < 160 ℃. It should be noted that all processes except those of the electrodes were conducted based on a solution process under ambient air conditions, not inside a N₂ filled glove box. It was found from the numerical calculations and experimental measurements that a lower photoconversion efficiency (PCE) for higher areas mainly comes from a degradation in the fill factor (FF). Solar cell characteristic parameters were measured under an AM1.5G spectrum (intensity of 100 mW/cm²), and the PCE was 1.8% and 2.0% for the OPV on the PEN and glass substrates, respectively.

Investigation of the electron transport layer in semitransparent organic photovoltaic cells using near-infrared light-absorbing materials

One challenge to realizing semitransparent organic photovoltaic (ST-OPV) cells is achieving both a high transmittance and high power conversion efficiency (PCE) simultaneously. We investigated the effect of using near-infrared light-absorbing materials in the different electron transport layer materials. Two materials were considered: zinc oxide (ZnO), which is used in conventional OPV cells, and tin oxide (SnO2), which has gained recent interest for its deposition at low temperatures suitable for flexible substrates. Experimental results showed that the ZnO- and SnO2-based ST-OPV cells had PCEs of 5.60% and 6.71%, respectively. The thickness of the organic active layer was varied to increase the transmittance in the visible light range. The SnO2-based ST-OPV cells were optimized to a thickness of 90 nm, which resulted in a PCE of 5.91%, average visible transmittance of 22.37%, and light utilization efficiency of 1.32%.

Manifestations of carbon capture-storage and ambivalence of quantum-dot &amp; organic solar cells: An indispensable abridged review

This study bestows an essential abridged review of the manifestations of carbon capture & storage (CCS) systems and the ambivalence of quantum-dot & organic photovoltaic (PV) solar cells. This research implicates that CCS system is evolving in capturing emissions from coal-fired electrical power stations to further mitigate climate change. Different manifestations are discussed for capturing and storing the with repercussions on operating costs, toxicity and energy efficiency. Chemical Looping Combustion appears to be the more energy efficient than Oxy-fuel CFBC and Ionic Liquids, and less expensive than Calcium Looping and Amine Scrubbing. Calcium Looping (Cal) and Ionic Liquids are also less toxic than Amine Scrubbing. Direct air technology is also very compelling at capturing emissions but highly expensive. Nevertheless, further research is still required for all CCS systems to be able to implement them widely in existing/new electrical power stations. Waste heat energy recovery systems can be used in conjunction with capture systems for further reduction of emissions. The ambivalence of quantum dot and organic solar cells are briefly reviewed. It implicates that composite film with enhanced quantum dot effects will make the film highly transparent and options of tunability of its color spectrum make the quantum dot solar cells highly attractive to a wide variety of applications. Organic solar cells are carbon-rich polymers and can be designed to improve a precise function of the cell, such as sensitivity to a certain type of light. OPV cells can only be considered as half-competent to crystalline silicon and have smaller beneficial lifespans, but could be less costly to produce in high volumes. Current research issues are substitution/compromises between electrical power conversion efficiency and average visible light transmittance. However, improving average light-transmittance decreases electrical power conversion efficiency and vice versa.

A methodology to simulate solar cells electrical response using optical-electrical mathematical models and real solar spectra

Herein we present a robust methodology to simulate the solar cells electrical response using optical-electrical finite-difference mathematical models and experimental data of solar spectrum. In this methodology, we suggest the use of mathematical PV models for three purposes: 1) to find the unknown solar cell electrical parameters from experimental J-V curves; 2) to simulate the response of solar cells under narrow-band incident radiation; and lastly 3) to simulate the short-circuit current response to experimental solar spectra. We used APE (Average Photon Energy) and SF (Spectral Factor) to assess the solar cells spectral response. We applied the method for data collected from the city of Belo Horizonte, Brazil. Both APE and SF analyses have shown that OPV presents relatively better spectral response than p-Si cells, because Belo Horizonte solar radiation is predominantly shifted to a blue-rich spectrum, compared to the AM1.5G. OPV cells show an annual average SF of 1.10, compared to the approximately 1.00 of p-Si cells. The methodology is presented in a workflow format, and we hope it will be useful for other researchers that are looking for procedures to simulate solar cells electrical response.

3D Cu ball-based hybrid triboelectric nanogenerator with non-fullerene organic photovoltaic cells for self-powering indoor electronics

Hybrid energy harvesters capable of capturing energy from multiple sources are gaining increasing attention. In this study, we develop the first hybrid organic photovoltaic cell−triboelectric nanogenerator (OPV–TENG) system targeting human activities indoors. The hybrid device comprises a non-fullerene OPV and a Cu ball-based TENG connected in series. Through optimization of an OPV cell, high power conversion efficiencies (15.03%–16.45%) are achieved for cells covering 50 mm 2 from indoor light sources. The Cu ball-based TENG effectively generates alternative electricity (electric power > 3 μW and charge up to 1.5 nC) by continuous contact−separation of the Cu balls due to human walking. The hybrid OPV–TENG system by stimulation/automatically harvests indoor light energy and mechanical energy from human motion. The total voltage/current outputs of the hybrid system are close to the sum of those generated from the OPV and TENG individually. Also, we demonstrate that a capacitor and a lithium-ion battery (LIB) are effectively and rapidly charged using an OPV–TENG-based hybrid self-charging device. Our study initiates developing hybrid OPV–TENG systems with extensive application potential for powering indoor electronics. • The hybrid system of TENG and OPV compensates vulnerable aspects of each device, thereby increasing power production. • Single OPV cell was created with PCEs ranging from 15.03% to 16.45% from indoor light sources. • Cu ball-based TENG yielded instantaneous power exceeding 3 μW and average charge up to 1.5 nC with walking speed of ~4.0 m/s. • The power-generating performance of the serially integrated OPV–TENG system is enhanced under indoor light and human motion. • This study highlights a promising method for collecting energy from multiple sources associated with human indoor life.

Highly‐Transparent and True‐Colored Semitransparent Indoor Photovoltaic Cells

AbstractOrganic photovoltaic (OPV) cells are promising indoor light energy harvesters because organic materials absorb strongly in the visible range. An indoor photovoltaic (IPV) device is an effective tool for the remote off‐grid wireless charging. However, as the indoor light fluxes are much weaker than the 1‐Sun condition, high‐performance indoor cells should have large areas in order to generate appreciable energies. They would then appear as flat, but expansive and dark objects if deployed indoors. Their presence would then alter the indoor lighting environment and affect visual perceptions. This work addresses the lighting and perception issues of IPV cells in three ways. i) A concept is proposed such that a high‐efficiency, semitransparent indoor OPV cell should possess an absorbance which is mismatched with the emission spectra of the light sources. ii) It is demonstrated that bulk heterojunction (BHJ) OPV solar cells with porphyrin donors can serve as high‐transparency and high‐efficiency indoor light harvesters. iii) Quantitative assessment criteria are presented for the transparency and chromaticity of an indoor semitransparent OPV cell, demonstrating that porphyrin‐based P2:PC71BM semitransparent BHJ cells can achieve a power conversion efficiency (PCE) exceeding 10%, and an illuminance transparency ~65%, while preserving the color perception of the light sources.

Thiophene- and Carbazole-Substituted N-Methyl-Fulleropyrrolidine Acceptors in PffBT4T-2OD Based Solar Cells.

The impact of fullerene side chain functionalization with thiophene and carbazole groups on the device properties of bulk-heterojunction polymer:fullerene solar cells is discussed through a systematic investigation of material blends consisting of the conjugated polymer poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2′;5′,2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) as donor and C60 or C70 fulleropyrrolidines as acceptors. The photovoltaic performance clearly depended on the molecular structure of the fulleropyrrolidine substituents although no direct correlation with the surface morphology of the photoactive layer, as determined by atomic force microscopy, could be established. Although some fulleropyrrolidines possess favorable lowest unoccupied molecular orbital levels, when compared to the standard PC71BM, they originated OPV cells with inferior efficiencies than PC71BM-based reference cells. Fulleropyrrolidines based on C60 produced, in general, better devices than those based on C70, and we attribute this observation to the detrimental effect of the structural and energetic disorder that is present in the regioisomer mixtures of C70-based fullerenes, but absent in the C60-based fullerenes. These results provide new additional knowledge on the effect of the fullerene functionalization on the efficiency of organic solar cells.

Organic tandem solar cells with 18.6% efficiency

Tandem organic photovoltaic (TOPV) cell is one of the technologies to harvest more solar power by staking two or more OPV devices on top of each other. Recently, the highest power conversion efficiency (PCE) ever achieved was 17.3%. Herein, this paper simulates the response of 676‬ different TOPV devices that consists front and back OPV cells. For this purpose, this paper uses the best 26 single-cell OPV devices to form the TOPV front and back cells combinations. The results show that there are some new TOPVs that can exceed 17.3% efficiency limit for TOPV. Also, in this work thickness optimization was performed for these new TOPV devices with an objective of efficiency maximization. As a result, using PBDTS-TDZ: ITIC in the front cells and PTB7-Th: O6T-4F:PC71BM in the back cell gives 18.6% efficiency. Likewise, the TOPV of PBDB-T-2F:TfIF-4FIC in the front cell with PTB7-Th:O6T-4F:PC71BM in the back cell gives 18.06% efficiency.

A study of the influence of plasmonic resonance of gold nanoparticle doped PEDOT: PSS on the performance of organic solar cells based on CuPc/C60

This work studied the role of gold nanoparticles (AuNPs) with different spherical sizes mixed with poly (3, 4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT: PSS) as a hole transfer layer to enhance the efficiency (ITO/PEDOT:PSS (AuNPs)/CuPc/C60/Al) organic photovoltaic cell (OPV). AuNPs were synthesized using the thermochemical method and the results of the transmission electron microscope (TEM) images showed that the gold nanoparticles mostly dominated by spherical shapes and sizes were calculated in the range (12–23 nm). Measurements of UV-VIS spectra for AuNPs have shown that the surface plasmon resonance shifted to a higher wavelength with decreasing the particle size. Surface morphology and absorption spectra of OPV cells were studied using atomic force microscope and UV-VIS spectrometer techniques. The efficiency of the OPV cell was calculated without and with AuNPs. Efficiency was increased from 0.78% to 1.02% due to the embedded of AuNPs with (12 nm) in PEDOT/PSS. The increase in the light absorption in CuPc is due to the good transparent conducting of PEDOT:PSS and the increase in the electric field around AuNPs embedded in PEDOT:PSS and inbuilt electric field at the interfacial between CuPc and C60 is due to the surface plasmon resonance of AuNPs. The increase in these two factors increase the exciton generation in CuPc, dissociation at the interfacial layer, and charge carrier transfer which increases the collection of electrons and holes at cathode and anode.

Synthesis, characterization and application of meso-substituted fluorinated boron dipyrromethenes (BODIPYs) with different styryl groups in organic photovoltaic cells

A series of highly fluorinated BODIPY dyes with different styryl aromatic donor groups such as phenyl, naphthyl and anthracyl were designed, synthesized, characterized and applied as electron-donor materials in organic photovoltaic cells (OPV). The introduction of the styryl moieties leads to a large bathochromic shift and to a significant decrease in the HOMO-LUMO energy-gaps. All the BODIPY dyes showed relatively low HOMO energies ranging from −5.21 to −5.54 eV as determined from cyclic voltammetry measurements. Furthermore, they all show good solubility in organic solvents, thermal stability, excellent film-forming abilities which added with the great optoelectronics characteristics makes them excellent candidates as electron-donor materials for OPV cells. The power conversion efficiency (PCE) of the OPV based on the best BODIPY blend (BDP3/PC70BM (1:2, w/w) was 2.8% with a high open circuit voltage (VOC) of 1.00 V, which is a very promising PCE result for BODIPY based OPV and a top VOC value for this kind of systems.

Area dependent behavior of bathocuproine (BCP) as cathode interfacial layers in organic photovoltaic cells

Standard and inverted configuration small molecule OPV cells incorporating bathocuproine (BCP) as electron transport and exciton blocking layer is investigated, demonstrating that 2 mm2 standard and inverted cells display a maximum performance for BCP thicknesses of 10 nm and 1.5 nm, respectively. The reason for the different optimum BCP thicknesses for the two device configurations is the BCP-metal complex formed between the Ag electrode and the BCP layer in the standard configuration OPV devices. Interestingly, at optimum BCP thicknesses, the inverted OPV cells outperform the standard devices. Upon up-scaling of the device area of the cells from 2 mm2 to 10 and 100 mm2, device failure becomes prominent for the inverted OPV cells, due to aggregation of the evaporated BCP layer on the ITO surface. This demonstrates that although BCP can be adopted for efficient ETL in inverted configuration OPV devices on small scale, it is not suitable for device up-scaling due to severely decreasing device yields. In this work, a possible solution where an ultrathin layer of C70 is evaporated between the ITO and BCP layer is proposed. It is demonstrated that the proposed solution holds a strong potential to minimize the device failures of the BCP based inverted OPV cells to a significant extent, while maintaining good device performances.

Synthesis and Characterization of a 2‐(1,1‐Dicyanomethylene) rhodanine‐based Nonfullerene Acceptor for OPVs

We synthesized an A–π–D–π–A‐type nonfullerene small molecule acceptor (Flu‐CNRH) based on fluorene and 2‐(1,1‐dicyanomethylene)rhodanine (CNRH) by a Knoevenagel condensation of the diformyl compound (Flu‐T‐CHO) and CNRH for the use as acceptors in organic photovoltaic cells (OPVs). Introduction of CNRH end groups effectively lowered the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the acceptor compared to those of the corresponding rhodanine‐based acceptor (Flu‐RH). The HOMO and LUMO levels of Flu‐CNRH are −5.71 and −3.60 eV, respectively. For comparison, Flu‐RH has HOMO and LUMO energy levels of −5.58 and −3.53 eV, respectively. This lowered LUMO energy level enables Flu‐CNRH to be combined with low bandgap polymer donors PTB7 and PTB7‐Th by providing proper LUMO offsets between donor and acceptor. OPV cells were fabricated with the device configuration of ITO/PEDOT:PSS/active layer/LiF/Al. The best power conversion efficiency of 1.47% was obtained in the P3HT:Flu‐CNRH devices at a D:A ratio of 1:1.5 and with annealing at 140°C. Moreover, Flu‐CNRH showed compatibility with low bandgap polymer donor PTB7 (1.22%) with external quantum efficiency response at a longer wavelength region up to 750 nm, while Flu‐RH had no photovoltaic behavior with PTB7 and PTB7‐Th.

Balanced Electric Field Dependent Mobilities: A Key to Access High Fill Factors in Organic Bulk Heterojunction Solar Cells

The compositions of most lab‐based bulk‐heterojunction (BHJ) solar cells are optimized by their power conversion efficiencies (PCEs). In this report, we suggest that the compositions should be optimized by their fill‐factors (FFs) instead. With the optimized‐FF approach, BHJ cells tend to have higher acceptor contents and possess better thermal and operational stabilities. Three model systems, namely, PTB7:PC71BM, PTB7‐Th:ITIC, and PBDB‐T:ITIC BHJs, are chosen as case studies. Charge carrier transport measurements are used to reveal the origin of the enhanced FFs of these BHJ solar cells. We demonstrate that these acceptor‐rich BHJs possess better balanced field‐dependent electron‐to‐hole mobility ratios due to improved electron mobilities near open‐circuit conditions. We introduce a new parameter, known as charge imbalance factor (Δ), to quantify the impact of field dependent mobilities on the FF of the OPV cells. The improved mobility ratio (reduced Δ) suppresses carrier recombinations (especially at the open‐circuit conditions). Despite having slightly reduced PCEs, the FF‐optimized cells enjoy a much better stability. Our results suggest that FF‐optimized BHJ cells with higher acceptor contents should be considered for practical applications, due to better thermal and operational stability.

Organic Photovoltaics with Non-Stoichiometric InZnSnO Thin Film Cathodes

Non-stoichiometric indium zinc tin oxide (IZTO) thin films were deposited onto glass substrates at 400 °C by DC magnetron sputtering using non-stoichiometric (In0.5Zn0.25−xSn0.25+xO1.5 and In0.4Zn0.3−xSn0.3+xO1.5, where x = ±0.05) IZTO ceramic targets. After deposition, all of the films were given annealing treatment at 450 °C in argon. The crystallization behavior was examined by X-ray diffraction, while the optical properties were measured by ultraviolet-visible spectroscopy, in which the average transmittance values higher than 80% were observed from all films. The minimum resistivity of approximately 6.3 × 10−4 Ω·cm was observed from the Sn-rich In0.5Zn0.2Sn0.3O1.5 film. The resistivity values of Sn-rich IZTO thin films were a little smaller than those of Zn-rich IZTO films. An OPV cell with the so-called inverted structure was fabricated using various IZTO films deposited under optimized conditions as the cathode electrode. It was found that the solar cell efficiency could reach up to 7.9% which is the same with the OPV cell with conventional ITO film.