Advances in the design and application of highly efficient conjugated polymers and small molecules over the past years have enabled the rapid progress in the development of organic photovoltaic (OPV) technology as a promising alternative to conventional solar cells. Among the numerous OPV materials, benzodithiophene (BDT)-based polymers and small molecules have come to the fore in achieving outstanding power conversion efficiency (PCE) and breaking 10% efficiency barrier in the single junction OPV devices. Remarkably, the OPV device featured by BDT-based polymer has recently demonstrated an impressive PCE of 11.21%, indicating the great potential of this class of materials in commercial photovoltaic applications. In this review, we offered an overview of the organic photovoltaic materials based on BDT from the aspects of backbones, functional groups, alkyl chains, and device performance, trying to provide a guideline about the structure-performance relationship. We believe more exciting BDT-based photovol...

Molecular Design of Benzodithiophene-Based Organic Photovoltaic Materials.

A multi-ring, ladder-type low band-gap polymer (PIDTCPDT-DFBT) is developed to show enhanced light harvesting, charge transport, and photovoltaic performance. It possesses excellent planarity and enhanced effective conjugation length compared to the previously reported fused-ring polymers. In order to understand the effect of extended fused-ring on the electronic and optical properties of this polymer, a partially fused polymer PIDTT-T-DFBT is also synthesized for comparison. The fully rigidified polymer provides lower reorganizational energy, resulting in one order higher hole mobility than the reference polymer. The device made from PIDTCPDT-DFBT also shows a quite promising power conversion efficiency of 6.46%. Its short-circuit current (14.59 mA cm−2) is also among the highest reported for ladder-type polymers. These results show that extending conjugation length in fused-ring ladder polymers is an effective way to reduce band-gap and improve charge transport for efficient photovoltaic devices.

Eleven-Membered Fused-Ring Low Band-Gap Polymer with Enhanced Charge Carrier Mobility and Photovoltaic Performance

To obtain a polymer based on benzodithiophene (BDT) owning both a largely extended π-conjugation system and a low-lying highest occupied molecular orbital (HOMO), a polymer (PBDTBzT-DTffBT) containing benzothienyl-substituted BDT is designed and synthesized. Compared with the polymer (PBDTT-DTffBT) based on thienyl-substituted BDT, PBDTBzT-DTffBT exhibits better thermal stabilities, red-shifted absorption spectra, and stronger intermolecular interactions. The HOMO and lowest unoccupied molecular orbital (LUMO) in PBDTBzT-DTffBT are decreased by 0.11 and 0.13 eV, respectively, which should be attributed to the contribution of the electron-withdrawing group benzene. Polymer solar cells (PSCs) based on PBDTBzT-DTffBT and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) exhibit a maximum power conversion efficiency (PCE) of 7.30% with a large open-circuit voltage of 0.90 V under AM 1.5G illumination (100 mW/cm2). The PCE is 36% higher than that of the PSCs derived from PBDTT-DTffBT. These findings provide ...

http://ir.qibebt.ac.cn/bitstream/337004/6324/1/Extending%20%cf%80-Conjugation%20System%20with%20Benzene%20An%20Effective%20Method%20To%20Improve%20the%20Properties%20of%20Benzodithiophene-Based%20Polymer%20for%20Highly%20Efficient%20Organic%20Solar%20Cells.pdf

Extending π-Conjugation System with Benzene: An Effective Method To Improve the Properties of Benzodithiophene-Based Polymer for Highly Efficient Organic Solar Cells

Harvesting energy directly from sunlight using photovoltaic technology has become an essential component of future global energy production. Although silicon-based inorganic materials still play a dominant role in the market, problems for inorganic materials-based solar cells mainly lie in (1) the high cost of production and technical difficulties in the fabrication of large-area cells and (2) supply of highly purified silicon. In contrast to inorganic photovoltaic materials, organic/polymer photovoltaic materials have currently become of broader interest owing to their great potential to bring about a major breakthrough in reducing the cost of solar cells. As a promising building block to construct narrow bandgap semiconductors for high-efficiency photovoltaics, structurally well-defined indacenodithiophene (IDT) and its derivatives have inspired great interest in the industrial and academic communities over recent years due to their rigidified and tunable coplanar fused ring aromatic structures, and 3D conformation as well. The aromatic fused-ring blocks efficiently restrain rotational disorder and consequently lower reorganization energy. An encouraging power conversion efficiency of more than 12% has been achieved in the IDT-based polymer solar cells. This review surveys recent research advances in the area of IDT-based conjugated materials for photovoltaic applications. The factors affecting the bandgaps, molecular energy levels, film morphologies, as well as the photovoltaic performance of these materials have also been discussed.

Indacenodithiophene: a promising building block for high performance polymer solar cells

Changing the π-bridge from thiophene to thieno[3,2-b]thiophene for the D–π–A type polymer enables high performance fullerene-free organic solar cells

A series of two-dimensional diketopyrrolopyrrole-based low band gap conjugated polymers were synthesized. Replacing thiophene with thieno[3,2-b]thiophene in the side chain and bridge resulted in significant changes to the optical, electrochemical, and morphological properties of the polymers, as well as the subsequent performance of devices made from these materials. The polymer with thieno[3,2-b]thiophene as a bridge instead of a side chain exhibited an increased absorption coefficient and hole mobility, and resulted in the highest power conversion efficiency (5.34%) in this series of polymers. This finding provides valuable insight for the development of more efficient low band-gap polymers.

The effect of thieno[3,2-b]thiophene on the absorption, charge mobility and photovoltaic performance of diketopyrrolopyrrole-based low bandgap conjugated polymers

Fluoro-benzoselenadiazole-based low band gap polymers for high efficiency organic solar cells

By using cyclopentadithiophene (CPDT) as an electron-rich unit, difluro-2,1,3-benzothiadiazole (DFBT), diketopyrrolopyrrole (DPP) and thienopyrroledione (TPD) as electron deficient units, two novel alternating conjugated copolymers with a D-A(1)-D-A(2) structure, PCPDT-DFBT-TPD and PCPDT-DFBT-DPP, were designed and synthesized. The incorporation of two electron-deficient units in the structure of terpolymer could enhance solubility, adjust band gap, optimize stack property, and change the electron distribution in the system. Both the polymers PCPDT-DFBT-TPD and PCPDT-DFBT-DPP show highly solubility in o-dichlorobenzene, chlorobenzene, and o-xylene. Optical bandgaps of these polymers can be estimated by extrapolating from the absorption edge of these films to be 1.56 eV for PCPDT-DFBT-TDP and 1.34 eV for PCPDT-DFBT-DPP. The power conversion efficiencies of 3.15 % for PCPDT-DFBT-TPD and 3.11 % for PCPDT-DFBT-DPP were achieved in a bulk heterojunction (BHJ) photovoltaic device with a configuration of ITO/PEDOT: PSS/Polymers: PC71BM/C-60-bis surfactant/Ag under the illumination of AM 1.5G at 100 mA cm(-2).

Synthesis and photovoltaic properties of conjugated copolymers containing cyclopentadithiophene and two different electron-deficient moieties in the polymer backbone

Chao Li

Papers

The effect of thieno[3,2-b]thiophene on the absorption, charge mobility and photovoltaic performance of diketopyrrolopyrrole-based low bandgap conjugated polymers

Fluoro-benzoselenadiazole-based low band gap polymers for high efficiency organic solar cells

Synthesis and photovoltaic properties of conjugated copolymers containing cyclopentadithiophene and two different electron-deficient moieties in the polymer backbone