Recent Advances in Bulk Heterojunction Polymer Solar Cells

Organic solar cells have desirable properties, including low cost of materials, high-throughput roll-to-roll production, mechanical flexibility and light weight. However, all top-performance devices are at present processed using halogenated solvents, which are environmentally hazardous and would thus require expensive mitigation to contain the hazards. Attempts to process organic solar cells from non-halogenated solvents lead to inferior performance. Overcoming this hurdle, here we present a hydrocarbon-based processing system that is not only more environmentally friendly but also yields cells with power conversion efficiencies of up to 11.7%. Our processing system incorporates the synergistic effects of a hydrocarbon solvent, a novel additive, a suitable choice of polymer side chain, and strong temperature-dependent aggregation of the donor polymer. Our results not only demonstrate a method of producing active layers of organic solar cells in an environmentally friendly way, but also provide important scientific insights that will facilitate further improvement of the morphology and performance of organic solar cells. The processing of high-performance organic solar cells usually requires environmentally hazardous solvents. Now, hydrocarbon-based processing is shown to achieve relatively high performance in a more environmentally friendly way.

Efficient organic solar cells processed from hydrocarbon solvents

A nonfullerene-based polymer solar cell (PSC) that significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.

Fullerene-Free Polymer Solar Cells with over 11% Efficiency and Excellent Thermal Stability

We thank the University of St Andrews for support. EZ-C thanks the Leverhulme Trust for financial support (RPG-2016-047). and the EPSRC (EP/P010482/1) for financial support.

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Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes.

ConspectusThe active layer in a solution processed organic photovoltaic device comprises a light absorbing electron donor semiconductor, typically a polymer, and an electron accepting fullerene acceptor. Although there has been huge effort targeted to optimize the absorbing, energetic, and transport properties of the donor material, fullerenes remain as the exclusive electron acceptor in all high performance devices. Very recently, some new non-fullerene acceptors have been demonstrated to outperform fullerenes in comparative devices. This Account describes this progress, discussing molecular design considerations and the structure–property relationships that are emerging.The motivation to replace fullerene acceptors stems from their synthetic inflexibility, leading to constraints in manipulating frontier energy levels, as well as poor absorption in the solar spectrum range, and an inherent tendency to undergo postfabrication crystallization, resulting in device instability. New acceptors have to address ...

Non-Fullerene Electron Acceptors for Use in Organic Solar Cells

Most polymer donors developed so far for high-performance non-fullerene OSCs are designed in planar molecular geometries containing BDT units. In this work, two donor–acceptor (D–A) conjugated polymers with wide band-gap, namely, PY3 and PY4, were designed and synthesized by introducing halogen atoms (F, Cl) into the donor units of polymers. We dismissed the π-bridge and fused it to the A unit (BTz), presenting a different electron-deficient unit labeled as fused-DTBTz, forming a D–A structure with halogenated BDT units. PY3 with fluorine has a deeper HOMO level and a slight bathochromic-shift compared with PY4 with a chlorine atom, and shows good thermal stability among the two polymers. The reasonable halogenated D-unit in D–A polymers is beneficial for effectively promoting the intermolecular packing and crystalline properties, and thus enhancing the charge separation and transfer as reported previously. The best-performing PY3:IT-4Cl-based device afforded a high PCE of 11.20% with a VOC of 0.798 V, a JSC of 19.09 mA cm−2, and an FF of 73.5%, and the OSCs based on PY4:IT-4F delivered a PCE of 12.51%, with a noticeably elevated VOC of 0.874 V, a JSC of 20.26 mA cm−2, and an FF of 70.7%. The results showed that chlorinated polymers have a more suitable energy level to match the acceptors than their fluorinated counterparts, thus effectively improving the FF and JSC of photovoltaic devices. Therefore, there is much room for enhancement in photovoltaic properties with rational halogenation of the D moiety of D–A polymers.

Manipulating the Intermolecular Stacking of Polymeric Donors for Efficient Organic Solar Cells

Recently, we have used terthiophene side chain to modify benzo[1,2-b:4,5-b']dithiophene (BDT) to form novel building block for BDT polymers. In this paper, this building block is used to copolymerized with thieno[3,4-c]pyrrole-4,6-dione (TPD) and thieno[3,4-b]thiophene (TT). This building block and TPD- or TT-based polymers (P1 and P3) show high open circuit voltage (V-OC) (ca. 0.9-0.95 V) and low energy loss (E-g-eV(OC)) in solar cells devices compared with similar polymers without bulky side chain. We further introduce thiophene pi bridge into these polymers backbone to form two other polymers (P2 and P4). We find this thiophene pi bridge does contribute to this bulky side chained benzodithiophene polymer photovoltaic performances, especially for power conversion efficiencies (PCEs). The polymer solar cells (PSCs) performances are moderate in this article due to the serious aggregation in the PSCs active layer. (C) 2015 Wiley Periodicals, Inc.

Thiophene π bridge effect on bulky side‐chained benzodithiophene‐based photovoltaic polymers

Low surface energy self‐polishing polymer grafted MWNTs for antibacterial coating and controlled‐release property of Cu2O

Synthesis and electrochemical polymerization of 9,9-bis(2-(2-(2-methoxy ethoxy)ethoxy)ethyl)-fluorene (EO-F) into poly[9,9-bis(2-(2-(2-methoxy ethoxy)ethoxy)ethyl)-fluorene] (EO-PF) films are reported. The boron trifluoride diethyl etherate electrolyte enables facile preparation of EO-PF films at lower potential compared to LiClO4/MeCN and the electrochemical polymerizations are discussed. The EO-PF shows good electrochemical behavior and can be dissolved in solvents such as DMSO and THF. The solubility of EO-PF in THF is 2 mg·mL−1 and the number average molecular weight is 35300 with a polydispersity index of 1.65. The side chains on C9 position of the monomer maintain unchanged after electrooxidation into corresponding polymer. The EO-PF dissolved in THF under 365 nm ultraviolet light is sky blue light emitting with the Commission Internationale de L’Eclairage-CIE coordinates of (0.19, 0.15). The electropolymerized EO-PF is used for the first time in chemosensing metal ions, demonstrating fluorescence quenching for Mn2+ and Fe3+ while fluorescence enhancement for Cr6+ ions.

Mingliang Sun

Papers

Manipulating the Intermolecular Stacking of Polymeric Donors for Efficient Organic Solar Cells

Thiophene π bridge effect on bulky side‐chained benzodithiophene‐based photovoltaic polymers

Low surface energy self‐polishing polymer grafted MWNTs for antibacterial coating and controlled‐release property of Cu2O

An electrochemically prepared sky-blue light emitting ether functionalized polyfluorene as chemosensor for metal ions

A medium-band-gap polymer based alkoxyl-substituted benzoxadiazole moiety for efficient polymer solar cells