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

Fabricating Binary Cathode Interface Layer by Effective Molecular Electrostatic Potential and Interfacial Dipole to Optimize Electron Transport and Improve Organic Solar Cell

A new monomer dithieno-[3′,2′:3,4;2′′,3′′:5,6]benzo[1,2-c]xadiazole (fDTBO) is first used as an electron-deficient acceptor to build D–A copolymers in a photovoltaic field. Two polymers PBDTT-fDTBO and PBDTO-fDTBO consist of fDTBO with thienyl-substituted-benzodithiophene (BDTT) or alkoxy-substituted benzodithiophene (BDTO). Both polymers show a deep HOMO around −5.5 eV with a wide band gap of over 1.9 eV. The polymer solar cells (PSCs) based on two polymers both show over 1 V high open circuit voltage (Voc) independent of polymer/PCBM ratios and solvent additives content in the PSCs active layer. The power conversion efficiency (PCE) based on PBDTT-fDTBO devices is 4.5% for single junction PSCs, and these polymers can be applied in tandem PSCs due to their wide band gap (up to 1.99 eV). This work demonstrates that the fDTBO unit is a promising building block to design wide band gap photovoltaic polymers with high Voc.

Novel wide band gap polymers based on dithienobenzoxadiazole for polymer solar cells with high open circuit voltages over 1 V

Alkoxyphenyl or alkylphenyl side-chained Thieno[2,3-f]benzofuran polymer for efficient non-fullerene solar cells

Incorporation of a classical visible non-fullerene acceptor into host binary blend enable ternary high-performance semitransparent polymer solar cells

Benzodithiophene (BDT)-based star-shaped molecule (12TBDT) was synthesized by Stille coupling reactions. The star-shaped molecule shows high decomposition temperature (447 degrees C), low-lying HOMO level (-5.52 eV), and wide UV vis absorption between 300 and 530 nm (E-g = 2.36 eV). DFT results show that the electron density of the HOMO and LUMO are localized on the thiophene and BDT groups. To the best of our knowledge, this is one of the earliest reports on star-shaped benzodithiophene molecules.

Mingliang Sun

Papers

Fabricating Binary Cathode Interface Layer by Effective Molecular Electrostatic Potential and Interfacial Dipole to Optimize Electron Transport and Improve Organic Solar Cell

Novel wide band gap polymers based on dithienobenzoxadiazole for polymer solar cells with high open circuit voltages over 1 V

Alkoxyphenyl or alkylphenyl side-chained Thieno[2,3-f]benzofuran polymer for efficient non-fullerene solar cells

Incorporation of a classical visible non-fullerene acceptor into host binary blend enable ternary high-performance semitransparent polymer solar cells

Synthesis and Optical-electronic Properties of a Novel Star-shaped Benzodithiophene Molecule