Transparent Organic Solar Cells Research Articles

Photopically Transparent Organic Solar Cells with Tungsten Oxide-Based Multilayer Electrodes.

The tailoring of the average photopic transmittance (APT) of transparent organic solar cells (T-OSCs) has been the greatest challenge in building-integrated photovoltaic applications for future smart solar windows to regulate indoor brightness, maintain a human circadian rhythm, and positively impact human emotions by allowing the observation of the external environment. However, a notorious trade-off exists between the APT and power conversion efficiency (PCE) of T-OSCs, mainly due to the absence of highly conductive and transparent top electrodes, which are a key building block determining the PCE and APT. Herein, we demonstrate a new tungsten oxide (WO3)-based multilayer as a highly conductive and transparent top electrode that provides an excellent APT while maintaining a high PCE in T-OSCs. With the assistance of optical simulation based on a transfer matrix method to calculate the optimum thicknesses of the multilayer electrodes, we achieve the best-performing T-OSC with a PCE of 7.0% and a full device APT of 46.7%, resulting in a high light utilization efficiency of 3.27%, which is superior to that of T-OSCs based on the same photoactive system. Furthermore, superior thermal stability at 85 °C in an N2 atmosphere is observed in WO3-based T-OSCs, maintaining 98% of the initial PCE after about 231 h. Our findings provide new insights into the development of T-OSCs with high efficiency and transparency.

Tackling Efficiency Challenges and Exploring Greenhouse-Integrated Organic Photovoltaics

Organic solar cells offer benefits such as transparent characteristics, affordability in manufacturing, and the ability to tailor light absorption properties according to specific needs. This review discusses challenges and recent strategies to enhance the power conversion efficiency of organic solar cells, such as bandgap tuning, molecular orbital alignment, active layer morphology engineering, electron-donating and -withdrawing group incorporation, side chain length engineering, a third additive’s insertion, and control of the solubility of materials. The good transparency of organic solar cells makes them ideal for greenhouse-integrated photovoltaics applications. By efficiently absorbing sunlight for photosynthesis and clean energy production, transparent organic solar cells optimize light management, enhance energy efficiency, and minimize overheating risks, resulting in more sustainable and efficient greenhouse operations. This review also evaluates organic solar cell integration in the greenhouse. The implementation of the strategies explored in this review can significantly impact a wide range of performance parameters in organic solar cells. These parameters include the optoelectronic properties, absorption spectrum, open circuit voltage, exciton dissociation, charge transport, molecular packing, solubility, phase separation, crystallinity, nanoscale morphology, and device stability. An optimized organic solar cell design is particularly beneficial for greenhouse-integrated photovoltaics, as it ensures efficient energy conversion and energy management, which are crucial factors in maximizing the performance of the greenhouse.

Selectively absorbing small-molecule solar cells for self-powered electrochromic windows

Dynamic control of solar transmission by photovoltaic-powered electrochromic smart windows is an up-and-coming approach towards the reduction of energy consumption in buildings. Selectively-absorbing transparent organic solar cells are capable of exhibiting excellent visible-light transparency as well as respectable power conversion efficiencies. This work presents three different transparent small-molecule solar cells (TSCs) with an area of 2.52 cm2, two of which are UV-absorbing and one of which absorbs in the NIR, each in combination with an organic electrochromic device (EC). The NIR-absorbing TSC uses a BDP-OMe:C60 combination, and has a power conversion efficiency of 4% with an average visible light transmission (AVT) of 40%. The two UV-harvesting systems, α-6T/B4PYMPM and NPB:B4PYMPM, each have an AVT of 50–65%, as well as high open-circuit voltages of 1.5–2.0 V. We demonstrate that these photogenerated voltages are sufficient to power a fluoran dye-based organic EC, which has excellent optical properties: its color ranges from highly transparent to deep black, and its on/off contrast ratio is higher than 80% in the range between 390 nm and 640 nm. Self-powered smart windows made by the combination of TSCs and ECs provide a way to significantly reduce energy consumption from air conditioning and lighting, towards zero-energy buildings.

Silver Nanowires Digital Printing for Inverted Flexible Semi‐Transparent Solar Cells

Transparent flexible organic solar cells (OSCs) are attracting increasing attention as an essential constituent for constructing smart window technologies and integrated photovoltaics (PVs). However, silver nanowire (AgNW) electrodes with negligible sheet resistance, good transmittance, and low costs are especially appealing in the design of flexible OSCs that require similar power conversion efficiency (PCE) values and superior flexibility compared with devices based on indium tin oxide (ITO) electrodes. Herein, the new digital printing technology of digital materials deposition to print the poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer and AgNWs as top and bottom electrodes for transparent flexible OSCs with an active layer as poly(3‐hexylthiophene) (P3HT):phenyl‐C61‐butyric acid methyl ester (PCBM) are used. All other thin layers are deposited on the polyethylene terephthalate (PET) substrate by the conventional process. The PV performance of the devices under inverted structure PET/AgNWs/ZnO/P3HT:PCBM/PEDOT/AgNWs is short circuit current density (Jsc) = 9.8 mA cm−2, open circuit voltage (Voc) = 0.53 V, fill factor (FF) = 0.60, and PCE = 2.9% with visible light transparency = 45%.

Net energy and cost benefit of transparent organic solar cells in building-integrated applications

Transparent photovoltaics is a new technology that can be used in buildings applications to simultaneously save energy and produce electricity. This study evaluates the potential of transparent photovoltaic (TPV) in window and skylight applications for four cities in the United States: Detroit, Los Angeles, Phoenix and Honolulu. Building energy demand simulation, photovoltaic generation, and life cycle assessment (LCA) are combined to evaluate the net energy benefit (NEB). The use of TPV on windows is evaluated for both new windows, for which the solar cell is deposited in the interior surface of the glass pane, and for the refurbishment of existing windows, for which plastic encapsulated solar cells are placed on the interior surface of existing windows. The NEB was found to be positive for all scenarios considered, and the cradle to gate energy to manufacture a transparent organic photovoltaic module was found to be negligible. The NEB was used to calculate the energy return on investment (EROI) and the energy payback time (EPBT). Both were found to be either better or comparable to other photovoltaic technologies. For glass modules, the best EROI was 102 in Phoenix for window and 208 in Honolulu for skylights. The EPBT varied from 51 days to 1.1 years, depending on the location and type of module. The use of transparent photovoltaics in the US was found to have both environmental and cost benefits due to the combined reduction in building energy consumption and electricity production.

Highly Transparent Organic Solar Cells with All‐Near‐Infrared Photoactive Materials

AbstractTransparent organic photovoltaics are identified as important components for building‐integrated photovoltaics and smart window technologies. In this work, highly transparent organic solar cells (T‐OSCs) based on all‐near‐infrared (NIR) harvesting materials (optical bandgap, < 1.4 eV) are first fabricated. Both donor and acceptor materials used in T‐OSCs exhibit great transparency in the visible region. After combining MoO3/Ag or MoO3/Ag/MoO3 transparent electrode, T‐OSCs show excellent visible light transmittance (VLT) of 52–61.5% with power conversion efficiencies of 3.5–4.2%. As far as it is known, this all‐NIR active layer represents the most visible transparent donor–acceptor combination in OSCs. In addition to high VLT, T‐OSCs have great aesthetic value, good color‐rendering index (CRI > 90), and high light energy utilization properties. This work highlights great potential of NIR photoactive materials for T‐OSCs.

Development of fullerene free acceptors molecules for organic solar cells: A step way forward toward efficient organic solar cells

Continuous strides are being made to explore non-fullerene acceptors for organic solar cells. Here, optoelectronic properties of four new acceptor-donor-acceptor (A-D-A) type non-fullerene acceptor molecules are evaluated for their potential use in organic solar cells. The designed molecules contain indacenodithiophene (IDT) donor core connected with various acceptor groups through benzothiadiazole (BT) bridge unit. The designed molecules differ from each other in end-capped acceptor groups. The end-capped acceptors are 2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (M1), 2,5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (M2), 2-methylene-2-H-indene-1,3-dione (M3), and 2,5-methylene-6-oxo-5,6-dihydrocyclopenta-c-thiphen-4-ylidene-malononitrile (M4). The optoelectronic properties are evaluated in comparison with the recently reported R which is structurally similar to the designed molecules. The reference compound R contains indacenodithiophene (IDT) donor core unit with 3-ethyl-d-ethylidene-2-thioxothiazolidin-4-one end capped acceptor group. The A-D-A acceptor molecules evaluated here exhibit proper frontier molecular orbital diagram to facilitate the charge mobility. M2, containing 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile end-capped acceptor group, exhibits maximum absorption at 805 nm which is attributed to extended conjugation with the BT unit. Results of transition density matrix (TDM) show clear effect of end caped acceptor group on electro-hole exciton. Small coupling of electron and hole in M4 illustrates easy dissociation of exciton as compared with other molecules. Among all, M4 shows the highest hole transfer rate as revealed from low hole reorganization energy (λh). The open circuit voltage (Voc) of reference R is 1.96 V with donor polymer PTB7-Th while the designed molecule M3 exhibits the Voc of 2.02 V. Hence, the designed fullerene free acceptor molecules are suitable for transparent organic solar cells.

Teaching Organic Electronics - Part II: Quick & Easy Synthesis of the (Semi-)Conductive Polymer PEDOT: PSS in a Snap-Cap Vial

Organic Electronics is an interdisciplinary and cutting-edge research field leading to innovative applications and products like ultra-thin and high-efficient organic LED displays, light-weight and transparent organic solar cells or printed organic field-effect transistors (to name only few). The core functional materials in such devices are organic (semi-)conductors like conjugated polymers, oligomers or small molecules. As a sequel to our former contribution in the World Journal of Chemical Education (Vol 6, No. 1), we present in this paper a hands-on, quick and easy experiment for the synthesis of the (semi-)conductive polymer PEDOT:PSS. This experiment can be integrated into laboratory trainings and enriches the portfolio for teachers and lab-instructors dealing with organic electronics.

Thienochrysenocarbazole based organic dyes for transparent solar cells with over 10% efficiency

Stable, transparent organic dye-sensitized solar cells were made with over 10% efficiencies.

Opto-electronic properties of non-fullerene fused-undecacyclic electron acceptors for organic solar cells

Due to limitations of fullerene based acceptor molecules for solar cell applications, research is recently diverted to explore non-fullerene acceptor molecules. In this regard, four new A-D-A type fused ring electron acceptor molecules (M1, M2, M3 and M4) are evaluated for their opto-electronic properties for transparent organic solar cells. These molecules contain strong electron donor undecacyclic linked with four different acceptor moieties, 2-(3-ethly-5-methylene-4-oxothiazolidin-2-yluidene)malononitrile (M1), 2-(5,6-dicyano-2-methylene-3-oxo -2,3-dihydroindene-1-ylidene)malononitrile (M2), 2-(5-methylene-6-oxo-tetrahydro-1H-cyclopenta-thiophene-4(5H)-ylidene)malononitrile (M3), and 3-ethyl-5-methylene-2-thioxothiazolidin-4-one (M4). The electronic and optical properties of these molecules are compared with the reference molecule R, which is recently reported as excellent non-fullerene based acceptor molecule. Among all molecules, M2 exhibits the maximum red shift where absorption appears 893.5 nm with B3LYP/6-31++G(d,p) level of theory due to highly extended conjugation between electron withdrawing end-capped acceptor moieties. The calculated Open circuit voltage (Voc) of reference molecule R is 1.78 eV with donor polymer PTB7-Th while molecule M2 exhibits the Voc value of 1.86 eV.

Roll-to-roll processing system for transparent organic solar cells designed and verified

Combination of two fabrication processes into continuous roll-to-roll manufacturing for organic solar cells is developed for both single junction and tandem cells compatible with a variety of molecules.

Metal-electrode-free Window-like Organic Solar Cells with p-Doped Carbon Nanotube Thin-film Electrodes.

Organic solar cells are flexible and inexpensive, and expected to have a wide range of applications. Many transparent organic solar cells have been reported and their success hinges on full transparency and high power conversion efficiency. Recently, carbon nanotubes and graphene, which meet these criteria, have been used in transparent conductive electrodes. However, their use in top electrodes has been limited by mechanical difficulties in fabrication and doping. Here, expensive metal top electrodes were replaced with high-performance, easy-to-transfer, aerosol-synthesized carbon nanotubes to produce transparent organic solar cells. The carbon nanotubes were p-doped by two new methods: HNO3 doping via ‘sandwich transfer’, and MoOx thermal doping via ‘bridge transfer’. Although both of the doping methods improved the performance of the carbon nanotubes and the photovoltaic performance of devices, sandwich transfer, which gave a 4.1% power conversion efficiency, was slightly more effective than bridge transfer, which produced a power conversion efficiency of 3.4%. Applying a thinner carbon nanotube film with 90% transparency decreased the efficiency to 3.7%, which was still high. Overall, the transparent solar cells had an efficiency of around 50% that of non-transparent metal-based solar cells (7.8%).

Visibly‐Transparent Organic Solar Cells on Flexible Substrates with All‐Graphene Electrodes

Portable electronic devices have become increasingly widespread. Because these devices cannot always be tethered to a central grid, powering them will require low‐cost energy harvesting technologies. As a response to this anticipated demand, this study demonstrates transparent organic solar cells fabricated on flexible substrates, including plastic and paper, using graphene as both the anode and cathode. Optical transmittance of up to 69% at 550 nm is achieved by combining the highly transparent graphene electrodes with organic polymers that primarily absorb in the near‐IR and near‐UV regimes. To address the challenge of transferring graphene onto organic layers as the top electrode, this study develops a room temperature dry‐transfer technique using ethylene‐vinyl‐acetate as an adhesion‐promoting interlayer. The power conversion efficiency achieved for flexible devices with graphene anode and cathode devices is 2.8%–3.8% at for optical transmittance of 54%–61% across the visible regime. These results demonstrate the versatility of graphene in optoelectronic applications and it is important step toward developing a practical power source for distributed wireless electrical systems.

Nanoantennas for enhanced light trapping in transparent organic solar cells

We propose a light-trapping structure offering a significant enhancement of photovoltaic absorption in transparent organic solar cells operating at infrared, while the visible light transmission keeps sufficiently high. The main mechanism of light trapping is related with the excitation of collective oscillations of the metal nanoantenna arrays, characterized by advantageous field distribution in the volume of the solar cell. It allows more than triple increase in infrared photovoltaic absorption.

Coevaporated calcium‐silver metal alloys as contact for highly transparent organic solar cells

AbstractWe present 10‐nm thick metal alloys created by coevaporation of calcium and silver as transparent top electrode for inverted bulk heterojunction small‐molecule organic solar cells (SMOSC). It is shown that such alloys exhibit sufficiently high conductivity to replace previously used thicker (>14 nm) pure Ag contacts. At the same time, Ca:Ag alloys have higher transmittance compared to pure Ag, which is desirable for semitransparent SMOSC where the light passes through the device and the metal contact. We find that a metal contact consisting of 1 nm Ag underlayer and 10 nm Ca:Ag of 1:1 mixing ratio (total Ag content by volume of 6 nm) on glass has an average transmittance in the visible range of 76% with a sheet resistance of 27.1 Ω/□, approaching the performance of ITO while being applied by a much gentler deposition method. Application of 10‐nm thick alloys in semitransparent SMOSC lead to transmittance in the visible range Tvis of up to 49% and efficiency η of up to 2.3%, showing superior performance compared to devices with pure Ag top contacts.

Transparent flexible organic solar cells with 6.87% efficiency manufactured by an all-solution process

We demonstrate that polyaniline (PANI) behaves as an anode buffer layer, which makes it an excellent hole transport layer. PANI was coated between the photoactive layer and the top anode in transparent flexible organic solar cells (OSCs). The performances of the devices with different PANI thicknesses were investigated. The results demonstrate that the power conversion efficiency (PCE) increased nearly four-fold with an 18 nm thick PANI layer compared to the reference cell without PANI. The optimum device performance with an 18 nm PANI layer exhibits a Jsc of 11.60 mA cm(-2), a V(oc) of 0.89 V, a FF of 66.87%, and thus a PCE of 6.87% under AM1.5G illumination of 100 mW cm(-2). The conversion efficiency of transparent flexible OSCs changes after 1500 bending cycles.

Highly efficient bifacial transparent organic solar cells with power conversion efficiency greater than 3% and transparency of 50%

In this work, we present vacuum-deposited bifacial transparent organic solar cells on indium-tin-oxide-coated glass substrates. Good performances and high transparencies are achieved simultaneously by employing the planar-mixed heterojunction of the organic donor 2-{[7-(5-N,N-ditolylaminothiophen-2-yl)-2,1,3-benzothiadiazol-4-yl]methylene}malononitrile (DTDCTB) and fullerenes with carefully designed resonance top electrodes. Comprehensive optical simulation is exploited to investigate the effect of the top-electrode configuration on the cell transparency and efficiency. Cells with structures designed for high transparencies were fabricated and tested. The DTDCTB:C60 device yields a high transmission of up to 66.4% at 530nm and a power conversion efficiency (PCE) of 2.11%. Moreover, the DTDCTB:C70 device demonstrates an exceptional PCE as high as 3.24% with a balanced transmission of ≈50% in the visible spectrum. Enhanced PCE values of transparent solar cells are also revealed with the use of external reflectors. Efficiency enhancements of ≈15% and ≈65% are achieved by simply attaching a reflection mirror at the cathode or anode side, respectively.

Vacuum-free processed transparent inverted organic solar cells with spray-coated PEDOT:PSS anode

Spray coating is a high throughput coating technique that is scalable and adaptable for organic photovoltaic manufacturing. To ensure uniform coating of the organic layers, the wettability, surface tension and boiling points of the solvents have to be optimized. Here, we used microscopic videos to understand the dynamics of the spray coating process. By optimizing the wettability and drying time of the PEDOT:PSS suspension on a hydrophobic surface, we attained a spray coated transparent anode without compromising on device performance. We further applied this vacuum-free process to a near infrared absorber to achieve a transparent organic solar cell with close to 60% transparency.

Photoelectron spectroscopy investigation of thin metal films employed as top contacts in transparent organic solar cells

The performance of transparent metal top contacts in organic solar cells can strongly be improved by employing surfactant layers. We use scanning electron microscopy to investigate the change in morphology upon insertion of an Al surfactant layer between 4,7-diphenyl-1,10-phenanthroline (BPhen) and a silver top contact. UV photoelectron spectroscopy measurements show the changes in energetic alignments at different steps of the organic/metal interface formation. Furthermore, using X-ray photoelectron spectroscopy depth profiling, we compare the differing intermixing processes happening within the two samples. Thereby, we can show that Al binds to BPhen molecules, acting as surfactant for subsequently deposited Ag layers, while Ag without any Al surfactant layer penetrates into and intermixes with the BPhen layer.