Free Polymer Solar Cells Research Articles

Wide bandgap D-A copolymers with same medium dithieno [2,3-e;3′2′-g]isoindole-7,9 (8H) acceptor and different donors for high-performance fullerene free polymer solar cells with efficiency up to 14.76%

Three new donor–acceptor conjugated polymers incorporating same dithieno [2,3-e;3′2′-g]isoindole-7,9 (8H) (DTID) as medium acceptor and different donors, i.e., dithienosilole (DTS) PDTID-DTS (P1), dithieno-benzene (DTB) PDTID-DTB (P2) and dibenzothiophene (BDT) PDTID-BDT (P3) as a donor have been synthesized and explored for non-fullerene based BHJ polymer solar cells (PSCs). These copolymers had optical band gaps of 1.83–2.07 eV and HOMO energy levels of −5.37 to −5.67 eV. The P2 consists of a DTB donor unit that results in a deeper HOMO level of −5.67 eV, which may be due to the weak electron-donating nature of DTB. Pairing with the narrow bandgap non-fullerene acceptor BThIND-Cl, the P1, P2, and P3-based PSCs showed overall power conversion efficiency of 14.76 %, 7.22 % and 13.13 %, respectively. The PSCs based on P2 and P1 showed the highest and lowest values of open-circuit voltage, respectively, consistent with their HOMO energy levels. The lowest value of PCE for P2 may be associated with the negative HOMO offset between the P2 and BThIND-Cl, which hamper the hole transfer from the HOMO of BThIND-Cl to P2, resulting in a low value of short circuit current and fill factor. The higher value of PCE of 14.76 % for P1 may be related to the broader absorption profile of the active layer and balanced charge transport, more appropriate nanoscale phase separation, and compact π-π stacking distance, leading to the high value of short circuit current and fill factor.

Roll-to-Roll Slot-Die-Printed Polymer Solar Cells by Self-Assembly.

Extremely simplified one-step roll-to-roll slot-die-printed flexible indium tin oxide (ITO)-free polymer solar cells (PSCs) are demonstrated based on the ternary blends of electron-donor polymer thieno[3,4- b]thiophene/benzodithiophene, electron-acceptor fullerene [6,6]-phenyl-C71-butyric acid methyl ester, and electron-extracting polymer poly[(9,9-bis(3'-( N, N-dimethylamino)propyl)-2,7-fluorene)- alt-2,7-(9,9-dioctylfluorene)] (PFN) at room temperature (RT) in ambient air. The flexible ITO-free PSC exhibits a comparable power conversion efficiency (PCE) with the device employing complicated two-step slot-die printing (5.29% vs 5.41%), which indicates that PFN molecules can migrate from the ternary nanocomposite toward the Ag cathode via vertical self-assembly during the one-step slot-die printing process in air. To confirm the migration of PFN, the morphology and elemental analysis as well as charge transport of different active layers are investigated by the in situ transient film drying process, transmission electron microscopy, atomic force microscopy, contact angle and surface energy, X-ray photoelectron spectroscopy, scanning electron microscopy, impedance spectroscopy, transient photovoltage and transient photocurrent, and laser-beam-induced current. Moreover, the good air and mechanical stability of the flexible device with a decent PCE achieved in 1 cm2 PSCs at RT in air suggests the feasibility of energy-saving and time-saving one-step slot-die printing to large-scale roll-to-roll manufacture in the future.

A New Electron Acceptor with meta-Alkoxyphenyl Side Chain for Fullerene-Free Polymer Solar Cells with 9.3% Efficiency.

A new small molecule acceptor, m‐ITIC‐OR, based on indacenodithieno[3,2‐b]thiophene core with meta‐alkoxyphenyl side chains, is designed and synthesized. The m‐ITIC‐OR film shows broader and redshift absorption compared to its solution and matched energy levels with a hexafluoroquinoxaline‐based polymer donor‐HFQx‐T. Here, polymer solar cells (PSCs) by blending an HFQx‐T donor and an m‐ITIC‐OR acceptor as an active layer deliver the power conversion efficiency (PCE) of 6.36% without any posttreatment. The investigations demonstrate that the HFQx‐T:m‐ITIC‐OR blend films possess higher and more balanced charge mobility, negligible bimolecular recombination, and nanoscale interpenetrating morphology after thermal annealing (TA) treatment. Through a simple TA treatment at 150 °C for 5 min, an impressive PCE of 9.3% is obtained. This efficiency is among one of the highest PCEs for additive free PSCs. This is the first time alkoxyphenyl side chain is introduced into nonfullerene electron acceptor; more interestingly, the new electron acceptor (m‐ITIC‐OR) in this work shows a great potential for highly efficient photovoltaic properties.

A fused-ring based electron acceptor for efficient non-fullerene polymer solar cells with small HOMO offset

A non-fullerene electron acceptor bearing a novel backbone with fused 10-heterocyclic ring (indacenodithiopheno-indacenodiselenophene), denoted by IDTIDSe-IC is developed for fullerene free polymer solar cells. IDTIDSe-IC exhibits a low band gap (Eg=1.52eV) and strong absorption in the 600–850nm region. Combining with a large band gap polymer J51 (Eg=1.91eV) as donor, broad absorption coverage from 300nm to 800nm is obtained due to complementary absorption of J51 and IDTIDSe-IC, which enables a high PCE of 8.02% with a VOC of 0.91V, a JSC of 15.16mA/cm2 and a FF of 58.0% in the corresponding PSCs. Moreover, the EQE of 50–65% is achieved in the absorption range of IDTIDSe-IC with only about 0.1eV HOMO difference between J51 and IDTIDSe-IC.

Dip-coating of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) anodes for efficient polymer solar cells

The fabrication of anodes and active layers by dip-coating in indium tin oxide (ITO)-free polymer solar cells (PSCs) is investigated. A highly conductive poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) layer was used as an anode while a blend film of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) was employed as an active layer. The transmittance and sheet resistance of dip-coated PEDOT:PSS layers prepared with different thickness were studied. These layers were integrated into PSCs. The PSCs with the dip-coated PEDOT:PSS and P3HT:PCBM films exhibited power conversion efficiencies of 3.21% and 3.03% on glass and polyethylene terephthalate substrates, respectively, comparable to those of conventional ITO-based cells. Our research results suggest the feasibility of fabricating PSCs without a traditional spin-coating process and the possibility to substitute the ITO electrodes for conducting polymer films using the facile dip-coating method.

Indium Tin Oxide-Free Polymer Solar Cells: Microcavity Enhancing the Performance Using WO3/Au/WO3as Transparent Electrode

Recently, indium tin oxide (ITO)-free polymer solar cells (PSCs) have attracted increasing attention due to expensive ITO price caused by rare and valuable element-indium. Here, we fabricated and investigated ITO-free PSCs with the structure of glass/WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Au/WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /poly (3-hexylthiophene): indene-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> bisadduct (P3HT:ICBA)/LiF/Al. It is demonstrated that the power conversion efficiency of ITO-free devices with 85-nm-thick active layer is improved by 21.2% compared with that of ITO-based. The improvement is attributed to the first-order resonance and near-resonance of microcavity effect constructed between the Au anode and top Al cathode. The judgment is supported by the incident photon-to-electron conversion efficiency spectra test and optical simulation based on transfer matrix method, which reveal that the microcavity structure can enhance light absorption within two discrete wavelength ranges of 390-460 and 510-660 nm.

All‐Solution‐Processed, Ambient Method for ITO‐Free, Roll‐Coated Tandem Polymer Solar Cells using Solution‐Processed Metal Films

AbstractA solution‐processed silver film is employed in the processing of top‐illuminated indium‐tin‐oxide (ITO)‐free polymer solar cells in single‐ and double‐junction (tandem) structures. The nontransparent silver film fully covers the substrate and serves as the bottom electrode whereas a PEDOT:PSS/Ag grid forms the semitransparent top electrode. All layers are roll‐coated/printed on a flexible substrate by using only two techniques: slot–die coating for up to 11 consecutive layers and flexo‐printing for the last Ag grid layer. The slot–die coated Ag film is compared to an evaporated Ag film in terms of surface morphological and topographical properties and to ITO in terms of flexibility. The slot–die coated Ag film demonstrates extremely low roughness (a root‐mean‐square roughness of 3 nm was measured over 240×320 μm2 area), is highly conductive (&lt;1 Ω/□), highly flexible, and cost‐effective in comparison to other reported metal films applied in polymer solar cells. Such properties result in high fill factors exceeding 50 % in both single and tandem structures on large‐area devices (1 cm2) and the corresponding efficiencies exceed 2 %.

Highly efficient ITO-free polymer solar cells based on metal resonant microcavity using WO3/Au/WO3 as transparent electrodes

Indium tin oxide (ITO)-free polymer solar cells (PSCs) with the structure of Glass/tungsten trioxide (WO3)/Au/WO3/PCDTBT: PC70BM/LiF/Al was fabricated and studied. The multilayer structure of WO3/Au/WO3 is used as the potential transparent electrode to replace ITO. Metal resonant microcavity, which can enhance light harvesting of active layers, was constructed between Au and Al electrodes. According to the J–V and IPCE characterization with 70nm active layer, power conversion efficiency (PCE) of the ITO-free microcavity device is approaching 4.55%, which is higher than that of the ITO-based device. However, PCE of the ITO-free device is much lower than that of the ITO-based device when the thickness of active layer increases to 130nm. The opposite experimental tendency leads to theoretical research toward the simulation of light absorption and optical electric field and the calculation of maximum short circuit current density (Jsc max) as a function of active layer thickness based on ITO-free and ITO-based devices. The research results show that microcavity effect is closely linked to intrinsic absorption of active layers.

Generic roll‐to‐roll compatible method for insolubilizing and stabilizing conjugated active layers based on low energy electron irradiation

ABSTRACTIrradiation of organic multilayer films is demonstrated as a powerful method to improve several properties of polymer thin films and devices derived from them. The chemical cross‐linking that is the direct result of the irradiation with ∼100 keV electrons is fast and has a penetration power compatible with thin plastic foils of one to two hundreds of microns typical of devices explored in organic electronics. We demonstrate here that active layers and complete devices can be subjected to electron irradiation‐induced cross‐linking thus facilitating multilayer solvent processing and morphological stability. The method is fast, generic, contactless, and fully compatible with high‐speed roll‐to‐roll processing of i.e. polymer solar cells at web speeds in excess of 60 m min−1. We employ fully printed, flexible, and foil‐based indium‐tin‐oxide free polymer solar cells in this study to demonstrate the technique. We also demonstrate that polymer solar cells are exceptionally stable towards ionizing radiation and find that doses as high as 100 kGy can be used before any significant decrease in performance is observed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40795.Together with Mokarian‐Tabari et al., J. Appl. Polym. Sci. (2014) 131, 40798, doi:10.1002/app.40798, this article is part of a Special Issue on Polymers for Microelectronics. The remaining articles appear in J. Appl. Polym. Sci. (2014) volume 131, issue 24. This note was added on 1st July 2014.

Polymer solar cells with inkjet‐printed doped‐PEDOT: PSS anode

In this article, we describe the development of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)‐based ink for the fabrication of indium tin oxide (ITO)‐free polymer solar cells (PSCs). The ink consisted of PEDOT:PSS, suitably doped with dimethyl sulfoxide (DMSO) in solution. The printed PEDOT:PSS showed electrical conductivity of 1000 S/cm and transparency around 85% in the visible range. Then, they were employed as anodes in ITO‐free polymer PSCs based on a bulk heterojunction of poly(3‐hexylthiophene) and [6,6]‐phenyl C61‐butyric acid methyl ester. The effects of surface treatments (O2 plasma, UV ozone) of glass substrates on the quality and morphology of the printed layer were investigated in order to improve the anode quality. The performances of the devices with printed polymeric anode were compared to the one realized depositing DMSO‐PEDOT:PSS by spin coating technique. The best cells performances were obtained by UV ozone treatment reaching a power conversion efficiency of 1.5%. POLYM. COMPOS., 34:1493–1499, 2013. © 2013 Society of Plastics Engineers

Efficient ITO-free polymer solar cells with pitch-converted carbon nanosheets as novel solution-processable transparent electrodes

We demonstrate that pitch-converted carbon nanosheet (CNS) films can efficiently function as transparent conducting electrodes for polymer solar cells (PSCs). The solution-processed CNS film was prepared with spin-coating of a cost-effective pitch solution dissolved in dimethylformamide on quartz substrates, followed by stabilization and carbonization treatments to convert the pitch into CNS. The pitch-converted CNS films prepared by the successive heat-treatment process were examined as a novel transparent anode in solar cells, and as a result, PSCs fabricated directly on such CNS electrodes exhibited a high power conversion efficiency of ∼1.7% under 100mWcm−2 illumination and AM 1.5G conditions. This approach could be highly desirable for advancing the realization of fully printable and flexible low-cost transparent electrodes for indium tin oxide (ITO)-free polymer solar cells.

OPV for mobile applications: an evaluation of roll-to-roll processed indium and silver free polymer solar cells through analysis of life cycle, cost and layer quality using inline optical and functional inspection tools

Organic photovoltaic modules have been evaluated for their integration in mobile electronic applications such as a laser pointer. An evaluation of roll-to-roll processed indium and silver free polymer solar cells has been carried out from different perspectives: life cycle assessment, cost analysis and layer quality evaluation using inline optical and functional inspection tools. The polymer solar cells were fabricated in credit card sized modules by three routes, and several encapsulation alternatives have been explored, with the aim to provide the simplest but functional protection against moisture and oxygen, which could deteriorate the performance of the cells. The analysis shows that ITO- and silver-free options are clearly advantageous in terms of energy embedded over the traditional modules, and that encapsulation must balance satisfying the protection requirements while having at the same time a low carbon footprint. From the economic perspective there is a huge reduction in the cost of the ITO- and silver-free options, reaching as low as 0.25 € for the OPV module. We used inspection tools such as a roll-to-roll inspection system to evaluate all processing steps during the fabrication and analyse the layers' quality and forecast whether a module will work or not and establish any misalignment of the printed pattern or defects in the layers that can affect the performance of the devices. This has been found to be a good tool to control the process and to increase the yield.

Indium tin oxide-free polymer solar cells using a PEDOT : PSS/Ag/PEDOT : PSS multilayer as a transparent anode

Cost-efficient indium tin oxide (ITO)-free polymer solar cells (PSCs) based on multilayer poly (3,4-ethylene dioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS)/Ag(15 nm)/PEDOT : PSS (PAP) as the anode were designed and achieved in this work. Compared with the ITO/PEDOT : PSS (IP) and Ag/PEDOT : PSS (AP) layers, the PAP layer showed acceptable optical transparency and electrical conductivity. The average transmittance (350–650 nm) and sheet resistance of PAP were measured to be 50.7% and 2.3 Ω, respectively. In addition, the PAP layer possessed low roughness characterized by atomic force microscopy. In order to investigate the photovoltaic properties of PSCs based on different anodes, devices with the configuration of PAP anode (or IP, AP anode)/poly(3-hexylthiophene) (P3HT) : 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM)/LiF/Al were fabricated. The PAP-based device exhibited reasonable photovoltaic behaviour compared with other devices, and the open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency were calculated to be 0.61 V, 7.01 mA cm−2, 0.69 and 2.99%, respectively. Therefore, PAP was a viable alternative to sputter-grown ITO electrodes, and cost-effective ITO-free PSCs based on a PAP anode could be realized according to this work.

Current Collecting Grids for ITO‐Free Solar Cells

AbstractIndium‐tin‐oxide (ITO) free polymer solar cells prepared by ink jet printing a composite front electrode comprising silver grid lines and a semitransparent PEDOT:PSS conductor are demonstrated. The effect of grid line density is explored for a large series of devices and a careful modeling study enabling the identification of the most rational grid structure is presented. Both optical and light beam induced current (LBIC) mapping of the devices are used to support the power loss model and to follow the evolution of the performance over time. Current generation is found to be evenly distributed over the active area initially progressing to a larger graduation in areas with different performance. Over time coating defects also become much more apparent in the LBIC images.

Polymeric anodes from poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) for 3.5% efficient organic solar cells

We present highly efficient indium tin oxide free polymer solar cells based on poly-(3-hexylthiophene-2,5-diyl) and C 61-bis-butric-acid-methyl-ester (P3HT:bisPCBM) comprising a polymeric anode from highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) formulations. The film conductivity was optimized by various additives. We found conductivities of almost 600 S/cm upon the addition of dimethylsulfoxide. The wetting properties of different PEDOT:PSS formulations were investigated by contact angle measurements. The optimized high conductivity in combination with the good film forming properties allow for the fabrication of highly efficient organic solar cells with an external power conversion efficiency of 3.5% with PEDOT:PSS as polymeric anode.