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

A novel monomer alkoxybiphenyl-substituted benzodithiophene (BDTBP) was synthesized and used as the donor to construct a donor–acceptor copolymer PBDTBP–DTffBT with 4,7-di(4-(2-ethylhexyl)-2-thienyl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT) as the acceptor unit. Compared with the corresponding polymer PBDTP–DTffBT based on alkoxyphenyl-substituted BDT, PBDTBP–DTffBT exhibits a red-shifted UV-vis absorption spectra due to its extended π-conjugation structure. The maximum power conversion efficiency (PCE) of PBDTBP–DTffBT based polymer solar cells (PSCs) is 6.70% with Voc = 0.85 V, Jsc = 12.72 mA cm−2 and FF = 62.14%, and the hole mobility is 3.45 × 10−4 cm2 V−1 s−1 while the maximum PCE of PSCs based on PBDTP–DTffBT is only 4.91% and the hole mobility is 1.70 × 10−5 cm2 V−1 s−1. These findings demonstrate that BDTBP unit is a promising building block for constructing a copolymer with high hole mobility, and extending the π-conjugation length on the alkoxyphenyl-substituted BDT is helpful to improve the photovoltaic properties.

Extending two-dimensional π-conjugation length by introducing the alkoxybiphenyl unit for efficient benzodithiophene based photovoltaic polymer

Photoelectrochemical cathodic protection (PECCP) as a branch of photocatalysis and photoelectrochemistry holds great promise for efficient anticorrosion. Organic semiconductors with tunable bandgap...

Small Organic Molecule Based Photoelectrodes for Efficient Photoelectrochemical Cathodic Protection

In order to investigate the effect of an (E)-1,2-di(thiophen-2-yl)ethene (TVT) unit on the hole mobility and photovoltaic properties of dithienyl-difluorobenzothiadiazole (DTBT) based polymers, two conjugated polymers PDT-DTBT-DT (thiophene backboned) and PTVT-DTBT-DT (TVT backboned) were synthesized. Compared to PDT-DTBT-DT, the backbone conformation of PTVT-DTBT-DT could be well modulated by the TVT unit, leading to an extended conjugation length and strengthened intermolecular interaction. Interestingly, it's found that the ultraviolet-visible (UV-vis) absorption peaks of the PTVT-DTBT-DT film was blue-shifted compared to that of the solution. The organic field-effect transistor (OFETs) characterization showed that PTVT-DTBT-DT possessed a high hole mobility of 0.12 cm2 V−1 s−1, which was higher than that of the counterpart PDT-DTBT-DT (0.04 cm2 V−1 s−1). Through simplified device optimization without any additives and annealing treatment, a power conversion efficiency (PCE) of 7.86% was achieved for PTVT-DTBT-DT with a short-circuit current density (Jsc) of 16.33 mA cm−2 and a fill factor (FF) of 68.92%, which is higher the PCE of 7.29% of PDT-DTBT-DT with a Jsc of 15.60 mA cm−2 and a FF of 66.62%. The PCE of 7.86% is among the highest PCEs reported for devices fabricated without any additives and thermal annealing treatment. The results revealed that PTVT-DTBT-DT as an ideal conjugated polymer could provide a greater possibility for the commercial application of PSCs, especially in terms of low cost and manufacturing convenience.

Mingliang Sun

Papers

Extending two-dimensional π-conjugation length by introducing the alkoxybiphenyl unit for efficient benzodithiophene based photovoltaic polymer

Small Organic Molecule Based Photoelectrodes for Efficient Photoelectrochemical Cathodic Protection

(E)-1,2-Di(thiophen-2-yl)ethene based high mobility polymer for efficient photovoltaic devices without any post treatment

Modifying the morphology via employing rigid phenyl side chains achieves efficient nonfullerene polymer solar cells

Carbazole side-chained benzodithiophene based two-dimensional D-A conjugated photovoltaic polymers