Flexible Organic Solar Cells Research Articles

Effect of anode interfacial modification on the performance of laminated flexible ITO‐free organic solar cells

AbstractLamination technique is one of the most promising and effective approaches to produce flexible organic solar cells (OSCs), with the combination of high throughput and simultaneous encapsulation. In this study, flexible ITO‐free OSCs were successfully fabricated by lamination technique under the optimized temperature and pressure. It is found that the introduction of hole interface layer of PEDOT:MoO3 helps to improve both the film hydrophobicity and the carrier extraction. A high efficiency improvement of about 30% is obtained in the interface‐modified laminating flexible ITO‐free OSCs compared to the conventional laminated device. This work illustrates that anode interface engineering has a significant effect on the improvement of performance of roll‐to‐roll laminated and self‐encapsulated OSCs.

Solution-Processed Transparent Conducting Electrodes for Flexible Organic Solar Cells with 16.61% Efficiency

HighlightsThe PEDOT:PSS flexible electrodes with a unique CF3SO3H treatment exhibited high electrical characteristics and stability.An energy level tuning effect was induced to create a suitable work function.Flexible organic solar cells yielded a record-high efficiency of 16.61%, a high flexibility, and a good thermal stability.

An efficiency of 14.29% and 13.08% for 1 cm2 and 4 cm2 flexible organic solar cells enabled by sol–gel ZnO and ZnO nanoparticle bilayer electron transporting layers

Flexible organic solar cells (OSCs) will be a promising energy harvest approach for portable and wearable electronics.

All annealing-free solution-processed highly flexible organic solar cells

We report efficient annealing-free solution-processed flexible organic solar cells (OSCs) integrated on a soft polyethylene substrate, with a high efficiency of 14.66% and a power-per-weight of 6.33 W g−1, close to that (15.73%) of thermally annealed control OSCs.

Doping and Design of Flexible Transparent Electrodes for High‐Performance Flexible Organic Solar Cells: Recent Advances and Perspectives

AbstractSubstantial effort has been devoted to both chemical doping and design of flexible transparent electrodes (FTEs) for flexible organic solar cells (OSCs) in the past decade. Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate), graphene, metal nanostructures, metal oxide/ultrathin metal/metal oxide, Mxene, and their hybrid electrodes emerge to be the most promising flexible conducting materials over indium tin oxide. The FTE fabrications play a critical role in flexible OSCs. This feature review article summarizes the current status on the researches of the FTEs including various approaches and strategies to boost the conductivity, work function, mechanical flexibility, wettability, etc, which directly affect the performances of the flexible OSCs. The most cutting edge progresses on both FTEs and flexible OSCs are highlighted along the line. Advantages and plausible issues are pointed out. Perspectives are provided that can advance the developments of the flexible OSCs. This review raises the awareness for the importance of developing plenty of FTEs and reveals their critical role in flexible OSCs.

Scalable, All‐Printed Photocapacitor Fibers and Modules based on Metal‐Embedded Flexible Transparent Conductive Electrodes for Self‐Charging Wearable Applications

AbstractThe popularity of wearable smart electronic gadgets, such as smartphones, smartwatches, and medical sensors, is inhibited by their limited operation lifetime due to the lack of a sustainable self‐charging power supply. This constraint can be overcome by developing a flexible, self‐charging photocapacitor that can synchronously harvest and store energy. Here, ultrathin, all‐printed, and metal‐embedded transparent conducting electrodes (ME‐TCEs) are designed for the fabrication of large‐area, flexible organic solar cells (F‐OSCs) and flexible supercapacitors (F‐SCs). Stripe‐shaped F‐OSCs (SF‐OSCs) and F‐SCs (SF‐SCs) are obtained via slitting the as‐fabricated F‐OSCs and F‐SCs with a surgical scalpel, respectively. The SF‐OSCs and SF‐SCs fully retain their performance after slitting, achieving a power conversion efficiency of ≈6.43% and areal capacitance of ≈52 mF cm−2, respectively. Furthermore, photocapacitor fibers are obtained by vertically stacking one SF‐OSC and seven SF‐SCs. Each fiber is fully encapsulated using UV‐curable resin. When woven into a textile, the photocapacitor module (2 series × 4 parallel connections) is able to charge up to a voltage of 3.2 V in 5 min under one‐sun illumination. The photoelectric‐conversion‐and‐storage efficiency (η) of the photocapacitor module is 4.94%. The highly tailorable, mechanically robust photocapacitor demonstrated herein can be a secondary, self‐sustainable power supply for futuristic wearable applications.

유연한 유기태양전지의 수분 투습 방지를 위해 원자층 증착법으로 제조된 Al 2 O 3 박막에 대한 연구

A moisture barrier layer with high density and uniformity is essential for increasing the lifespan of optoelectronic devices such as flexible organic solar cells, LEDs, and photodetectors. In this study, various surface pre-treatments (O2 plasma, UVO treatment, Al seed layer, and thermal annealing process) were performed on a polyethylene naphthalate (PEN) film to form a functional group of chemical adsorption with the atomic layer deposition (ALD) precursor. We investigated the effect of the surface pre-treatment of a PEN substrate for a deposition of Al2O3 thin film in terms of the deposition uniformity and water vapor transmittance rate (WVTR). For example, the root mean square roughness of the bare PEN film/Al2O3 was RRMS=3.26 nm, whereas the O2 plasma treated PEN film/Al2O3 had RRMS=0.99 nm because of the presence of a functional group. As a result, WVTR of bare PEN film/Al2O3 was 0.83 g/m²/day, whereas that of O2 plasma treated PEN film/Al2O3 decreased to 0.38 g/m²/day.

Regulating crystallization to maintain balanced carrier mobility via ternary strategy in blade-coated flexible organic solar cells

Regulating the crystallization of donor and acceptor to maintain balanced carrier mobility is of great importance to fabricate efficient organic solar cells (OSCs). Herein, the balanced crystallinity between donor and acceptor was finely controlled in blade-coated OSCs. By adding high crystalline FOIC into PBDB-T:ITIC system, a balanced carrier mobility was achieved, resulting in the much improved fill factor. The optimized ternary device exhibits an increased current density, due to the enhanced light-harvesting efficiency with complementary absorption and the morphology change. Morphology characterization demonstrated that the ternary film exhibits a highly balanced crystallinity between the donor and acceptor on account of the formation of acceptor alloy. Moreover, the ternary film not only possesses a small domain size, but also exhibits a high domain purity as compared to both binary films. Encouragingly, a highest power conversion efficiency (PCE) of 10.68% was obtained for the blade-coated ternary OSCs. In addition, the blade-coated flexible large-area (105 mm 2 ) OSC based on PBDB-T:ITIC:FOIC ternary system also exhibits a high PCE of 9.81%, showing great potential in the high-throughput fabrication of OSCs. The crystallization was finely regulated by ternary strategy to balance the carrier mobility in blade-coated flexible organic solar cells. • The crystallization was finely regulated in blade-coated OSCs by adding high crystalline FOIC into PBDB-T:ITIC system. • High PCE of 10.68% with excellent fill factor (69.8%) was achieved for the blade-coated PBDB-T:ITIC:FOIC device. • Large-area (105 mm 2 ) flexible device was fabricated by blade-coating in air, and exhibits a high PCE of 9.81%.

Benefits, Problems, and Solutions of Silver Nanowire Transparent Conductive Electrodes in Indium Tin Oxide (ITO)‐Free Flexible Solar Cells

AbstractIn this review, silver nanowires (AgNWs) are introduced, as the primary material to replace indium tin oxide for fabricating cost‐effective flexible organic solar cells (FOSCs), because of their remarkable solution‐processing, flexibility, transparency, and conductivity, along with their enhanced properties in terms of light‐scattering, plasmonic effects, and transmittance in the near infrared region. The drawbacks of AgNWs, particularly their high roughness, low adhesion to substrates, atmospheric corrosion, degradation under UV and visible light, and poor contact at wire‐wire junctions, must be resolved prior to their use in commercial FOSCs applications. Herein, comparisons among all candidates (e.g., graphene, carbon nanotubes, metal grids, and conducting polymers), along with a report of all recent progress in addressing these issues for using AgNWs as flexible transparent conductive electrodes (TCEs), are discussed. In addition, recent publications on the fabrication of highly efficient FOSCs based on AgNWs are summarized. The discussed issues regarding AgNWs‐TCEs apply not only to FOSCs, but can be generalized for other third‐generation solar cells, such as perovskite solar cells and dye‐sensitized solar cells; additionally, they provide insight for other optoelectronic applications, such as organic light‐emitting diodes, liquid crystal displays, smart windows, touch panels, and heaters.

Synergistic Optimization Enables Large-Area Flexible Organic Solar Cells to Maintain over 98% PCE of the Small-Area Rigid Devices.

Slot-die coating is generally regarded as the most effective large-scale methodology for the fabrication of organic solar cells (OSCs). However, the corresponding device performance significantly lags behind spin-coated devices. Herein, the active layer morphology, flexible substrate properties, and the processing temperature are optimized synergistically to obtain high power conversion efficiency (PCE) for both the flexible single cells and the modules. As a result, the 1 cm2 flexible devices produce an excellent PCE of 12.16% as compared to 12.37% for the spin-coated small-area (0.04 cm2 ) rigid devices. Likewise, for modules with an area of 25 cm2 , an extraordinary PCE of 10.09% is observed. Hence, efficiency losses associated with the upscaling are significantly reduced by the synergistic optimization. Moreover, after 1000 bending cycles at a bending radius of 10mm, the flexible devices still produce over 99% of their initial PCE, whereas after being stored for over 6000 h in a glove box, the PCE reaches 103% of its initial value, indicating excellent device flexibility as well as superior shelf stability. These results, thus, are a promising confirmation the great potential for upscaling of large-area OSCs in the near future.

Practically Viable Approach to Efficient and Reliable Semitransparent Flexible Organic Solar Cells: Face‐Seal Encapsulation Embedded with Tailored Color‐Control Functionality

The success of semitransparent organic solar cells (ST‐OSCs) depends heavily on whether they can achieve high efficiency while meeting the conditions for high transmittance or target apparent color. Herein, a device architecture for ST‐OSCs that achieves both enhanced efficiency and controlled apparent color or high transmittance is proposed, while providing protection from ambient air. In the proposed scheme, cells are encapsulated by a barrier foil embedded with a color‐controlling dielectric mirror (CCDM) structure, which is tailored for selective reflection at the targeted spectral band and transmission in the other spectral band. This approach effectively enhances the photocurrent with little compromise in transmittance, yet it allows control of the color of ST‐OSCs. Preparing these CCDMs independently of cell fabrication, the best material composition is utilized without damaging the underlying layers. With the proposed approach, ST‐OSCs with an efficiency of 8.30% and luminous transmittance over 30.4% are demonstrated. Furthermore, by setting ST‐OSCs in the neutral plane utilizing face‐seal encapsulation geometry, it is shown that these devices can maintain 98% of the initial efficiency even after 2000 cycles of repeated bending at a strain of 0.5%. Moreover, they can maintain initial efficiency very well in a highly damp condition for 120 h.

Enhancement of efficiency and stability in organic solar cells by employing MoS2 transport layer, graphene electrode, and graphene quantum dots-added active layer

For enhancing efficiency and flexibility of organic solar cells, new constituent materials are highly required. Here, we first report flexible organic solar cells (FOSCs) by employing MoS2 hole transport layer (HTL), bis(trifluoromethanesulfonyl)-amide-doped graphene (TFSA-GR) transparent conductive electrode (TCE), and GR quantum dots (GQDs)-added active layer. Power conversion efficiency (PCE) of the FOSCs without GQDs strongly depends on number of layers (Ln) of MoS2 as well as on doping concentration (nD) of TFSA-GR, thereby showing maximum PCE of 3.56% at Ln = 2 and nD = 20 mM, resulting from the lowest resistance at the TCE/MoS2/active layer interfaces. The long-term stability of the FOSCs is almost two times better than that of their counterparts with conventional organic HTL. By adding GQDs in the active layer, the PCE is further enhanced to 4.23% and is maintained at 89/82% of the original value after inner/outer repeated bending tests for 1000 cycles, respectively, indicating outstanding mechanical stability. These results suggest that GQDs are very useful for the active layer of FOSCs with better PCE and flexibility.

Performance enhancement of organic/Si solar cell using CNT embedded hole selective layer

In this work, we present a simple and solution-based synthesis approach to combine the virtues of PEDOT:PSS and carbon nanotube (CNT) by developing a composite film and their application as a hole selective layer (HSL) in organic-silicon hybrid heterojunction solar cell. The heterojunction solar cell with the optimised PEDOT: PSS-CNT HSL showed a notable open-circuit voltage (Voc) of 588.6 mV, short circuit current density (Jsc) of 25.3 mA/cm2 and fill factor (FF) of 60.79% yielding a photo-conversion efficiency (η) of 9.05%. The pristine PEDOT:PSS/Si device obtained an η of 6.2% with a Voc of 502 mV. The role of CNT in the charge transport mechanism and improving Voc was corroborated by employing various characterisation methods such as J-V, C-V, and electrochemical impedance spectroscopy. The composite layer induced a strong inversion layer in silicon and enhanced the device performance. The application of PEDOT:PSS-CNT composite film is not limited to c-Si solar cells, but can also be used to fabricate flexible organic and perovskite solar cells.

Electrically stable Ag nanowire network anodes densely passivated by a conductive amorphous InSnTiO layer for flexible organic photovoltaics

An electrically stable Ag nanowire (Ag NW) network was fabricated by passivating with a conductive amorphous InSnTiO (ISTO) layer. It could be used in flexible transparent conductive electrodes for flexible organic photovoltaics. By plasma damage-free sputtering of amorphous ISTO on Ag NWs, sulfurization of Ag NWs was effectively prevented without sacrificing sheet resistance (44.5 Ω/sq.), optical transmittance (87.2%), or mechanical flexibility. Flexible organic solar cells (OSCs) fabricated on ISTO covered Ag NW network anodes showed slightly higher power conversion efficiency (5.94%) than reference OSCs with ITO anodes (5.79%). These results demonstrate that passivation of Ag NWs by amorphous conductive ISTO is a useful approach to improving the reliability of Ag NW network electrodes for high-performance flexible OSCs because the amorphous compact structure can effectively prevent the diffusion of sulfur from ambient air.

Extremely efficient flexible organic solar cells with a graphene transparent anode: Dependence on number of layers and doping of graphene

Graphene has shown tremendous potential as a transparent conductive electrode (TCE) for flexible organic solar cells (OSCs). However, the trade-off between electrical conductance and transparency as well as surface roughness of the graphene TCE with increasing layer number limits power conversion efficiency (PCE) enhancement and its use for large-area OSCs. Here, we use a 300 nm-thick poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester blend as the photoactive layer and a benzimidazole (BI)-doped graphene as the transparent anode to demonstrate efficient OSCs with good flexibility. It is found that 3 layer (L) graphene had the best balance between sheet resistance, optical transmittance and surface roughness for optimized cell design. A 0.2 cm2 cell with a 3L BI-doped graphene anode had a PCE of 6.85%, which is one of the highest PCE values reported so far for flexible graphene anode-based OSCs. The flexible cells were mechanically robust, showing only a small performance degradation during up to 250 flexing cycles. Moreover, the combination of the thick photoactive layer with the optimized 3L BI-doped graphene TCE enabled production of 1.6 cm2 flexible OSCs with a PCE of 1.8%. Our work illustrates the importance of graphene TCE development for flexible OSCs as well as other wearable optoelectronic devices.

Green poly-lysine as electron-extraction modified layer with over 15% power conversion efficiency and its application in bio-based flexible organic solar cells

Abstract In this study, we first revealed a green material-Poly-lysine as an interfacial layer (IFL) of electron-extraction layer (EEL) and investigated evolution of morphologies of the active layers in organic photovoltaics (OPVs). The surface structure of the active layers was characterized by atomic force microscopy (AFM) and the molecular packing features were revealed by grazing-incidence wide-angle X-ray scattering (GIWAXS). By embedding poly-lysine as IFL, we evidenced the changes of the blend film phase segregation and observed an increase order of molecular packing in preferential face-on orientation. The optimized blend film morphology facilitated the carrier extraction, thereby significantly improved the OPV performance with the best power conversion efficiency (PCE) of 12.5% and 15.3% for the PBDB-T-2Cl:IT-4F and PBDB-T-2F:Y6 blends, respectively. Compared with the controlled devices, the poly-lysine-modified devices showed significantly improved thermal-and photo-stability which keeps 80% of its initial efficiency after 400-h heating and illumination. As the first discovery of its general applicability of the promising IFL material, poly-lysine was further applied to fabricate a flexible OPV device using 100% bio-based polyethylene furandicarboxylate (PEF) substrate and its derived OPV device exhibited a PCE greater than 7% and maintained the 80% efficiency under the high bending radius of 3 mm. The present study suggests the potential application of using bio-based materials for flexible OPV applications.

ITO and graphene-covered Ag grids embedded in PET substrate by thermal roll imprinting for flexible organic solar cells

The development of a low-resistive flexible transparent conductive film (TCF) was demonstrated by showing thermal roll imprinted and an embedded Ag grid. The Ag-embedded TCF shows excellent optical and electrical properties when the secondary layer of ITO and graphene is coated onto the flexible embedded Ag grid substrate. The TCF showed an extremely high transmittance of 77.56% with ITO and 77.73% with graphene; moreover, it showed a very low sheet resistance of 4.05 Ω/□ and 14.0 Ω/□ with ITO and graphene, respectively. This high performance is achieved by thermal imprinting of channels at 15 μm wide so that the DI-based nano silver paste filled in the narrow channels using Dr. Blade's method, thus providing the embedded pattern of Ag grid in the flexible PET substrate. The succeeding TCF performance was validated by fabrication of an OSC (organic solar cell) that exhibits excellent power conversion efficiency (PCE) of 2.649% and 2.551% for the ITO-Ag grid and graphene-Ag grid, respectively. This indicates that the hybrid flexible electrode using an intaglio method can be applied to transparent conducting electrodes for highly efficient opto-electronic devices.

Stability of Non-Flexible vs. Flexible Inverted Bulk-Heterojunction Organic Solar Cells with ZnO as Electron Transport Layer Prepared by a Sol-Gel Spin Coating Method

In this research, inverted bulk heterojunction organic solar cells (BHJ OSC) with poly(3-hexylthiophene-2,5-diyl): (6,6)-phenyl C61 butyric acid methyl (P3HT:PCBM) as the active layer were fabricated by a sol-gel spin coating method using flexible PET and non-flexible glass as substrates. The power conversion efficiency (PCE) and the stability of the cells were investigated. According to the results, the non-flexible device showed higher short circuit current (Jsc) as well as open-circuit voltage (Voc) as compared to the flexible one so that 2.52% and 0.67% PCE for non-flexible and flexible cells were obtained, respectively. From the stability point of view, the non-flexible device maintained 51% of its initial efficiency after six weeks in a dark atmosphere, while it was about 19% for the flexible cell after four weeks. The most important reason for the higher PCE with the higher stability in the non-flexible cell can be attributed to its higher shunt resistance (Rsh) and better interlayer connections at the electron collector side.

Biomimetic Electrodes for Flexible Organic Solar Cells with Efficiencies over 16%

AbstractFlexible organic solar cells (OSCs) are very promising for use in portable power supply devices due to the advantages of low‐cost, light‐weight, and flexibility. However, the efficiencies of flexible OSCs are limited by the flexible transparent electrodes owing to their nonoptimal electrical, optical, and mechanical properties. To address these challenges, leaf‐like biomimetic electrodes are proposed to achieve an efficient light capture and glossy surface for a high‐efficiency flexible OSC. To mimic the internal anatomy of the leaf, the conformable electrode stack consists of a flexible polyimide substrate, light‐scattering polystyrene spheres, zinc oxide protecting layer, and electrically conductive silver nanowires to obtain a high transmittance, low sheet resistance, and low surface roughness. A record‐high power conversion efficiency of 16.1% is realized by a flexible OSC with the biomimetic electrode design, comparable to those rigid devices on glass. Moreover, the flexible OSC on this biomimetic electrode exhibits a robust bendability against flexural strain, retaining 85% of the initial efficiency after 5000 bending cycles at a radius of curvature as small as 1.0 mm.

Semitransparent Flexible Organic Solar Cells

Abstract The semitransparent flexible organic solar cell takes advantages of flexibility, transparency, color adjustment property, which is more conducive to integrate on buildings and mobile terminals. Ascribing to the developments of narrow band gap donors and the new non-fullerene acceptors, the power conversion efficiency of semitransparent flexible organic solar cells has been achieved 10% to 12% with average visible transmittance of 17% to 21%. This review summarizes the molecular design of the most representative active layer materials, and discusses the characterization of semitransparent parameters paradigms, then we discuss how to optimize the device in combination with optical simulation, and finally list the recent development of semitransparent flexible electrodes of ITO-free organic solar cells, and give our perspectives on the next step direction.