Organoboron molecules and polymers for organic solar cell applications

Organic solar cells (OSCs) are emerging as a new photovoltaic technology with the great advantages of low cost, light-weight, flexibility and semi-transparency. They are promising for portable energy-conversion products and building-integrated photovoltaics. Organoboron chemistry offers an important toolbox to design novel organic/polymer optoelectronic materials and to tune their optoelectronic properties for OSC applications. At present, organoboron small molecules and polymers have become an important class of organic photovoltaic materials. Power conversion efficiencies (PCEs) of 16% and 14% have been realized with organoboron polymer electron donors and electron acceptors, respectively. In this review, we summarize the research progress in various kinds of organoboron photovoltaic materials for OSC applications, including organoboron small molecular electron donors, organoboron small molecular electron acceptors, organoboron polymer electron donors and organoboron polymer electron acceptors. This review also discusses how to tune their opto-electronic properties and active layer morphology for enhancing OSC device performance. We also offer our insight into the opportunities and challenges in improving the OSC device performance of organoboron photovoltaic materials.

BODIPY-Based Molecules, a Platform for Photonic and Solar Cells

The 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based molecules have emerged as interesting material for optoelectronic applications. The facile structural modification of BODIPY core provides an opportunity to fine-tune its photophysical and optoelectronic properties thanks to the presence of eight reactive sites which allows for the developing of a large number of functionalized derivatives for various applications. This review will focus on BODIPY application as solid-state active material in solar cells and in photonic devices. It has been divided into two sections dedicated to the two different applications. This review provides a concise and precise description of the experimental results, their interpretation as well as the conclusions that can be drawn. The main current research outcomes are summarized to guide the readers towards the full exploitation of the use of this material in optoelectronic applications.

BODIPY bearing alkylthienyl side chains: a new building block to design conjugated polymers with near infrared absorption for organic photovoltaics

A new benzene-fused BODIPY unit for designing polymer donors with near-infrared absorption for organic photovoltaics.

BODIPY derivatives with near infra-red absorption as small molecule donors for bulk heterojunction solar cells

The study of small donor molecules as the active component of organic solar cells continues to attract considerable attention due to the range of advantages these molecules have over their polymeric counterparts. Here we report the synthesis and solar cell fabrication of three BODIPY small molecule donors. Two of the dyes feature triphenylamine and phenothiazine as donor units attached to the meso and α-positions of the BODIPY core (TPA-PTZ-DBP and PTZ-TPA-BDP). Additionally, we have synthesised a push–pull derivative featuring phenothiazine moieties in the α-positions and a nitrobenzene in the meso-position (N-TPA-BDP) in order to investigate what effect this type of functionalisation has on the photovoltaic properties compared to the other dyes. The optoelectronic properties were investigated and the dyes showed broad absorption in the near-infrared with high extinction coefficients. Electrochemical measurements indicated good reversibility for the dyes redox processes. In contrast with the all-donor functionalised systems, N-TPA-BDP demonstrated extensive HOMO–LUMO overlap by DFT. The dyes were investigated as donor molecules in bulk heterojunction solar cells along with PC₇₁BM, and under optimal donor to acceptor ratio PTZ-TPA-BDP showed the highest PCE of 1.62%. N-PTZ-BDP:PC₇₁BM was the only blend to further improve upon thermal annealing reaching the highest conversion efficiency among the dyes of 1.71%. A morphology comprised of finely mixed donor and acceptor components is observed for BHJ blends of each of the three donors at their optimum fullerene content. Upon thermal annealing, these morphological features remain mostly the same for PTZ-TPA-BDP:PC₇₁BM and TPA-PTZ-DBP:PC₇₁BM blends whereas for N-PTZ-BDP:PC₇₁BM the domains show a larger size. These dyes show that phenothiazine functionalisation of BODIPY is useful for solar cells because it gives strong and broad absorption extending to the near infra-red and materials with reversible redox properties – both of which are desirable for organic solar cells.

We report the synthesis of donor/acceptor functionalised BODIPY derivatives and their incorporation as donor molecules in bulk heterojunction solar cells.

BODIPY-Based Semiconducting Materials for Organic Bulk Heterojunction Photovoltaics and Thin-Film Transistors

The rapid emergence of organic (opto)electronics as a promising alternative to conventional (opto)electronics has been achieved through the design and development of novel π-conjugated systems. Among various semiconducting structural platforms, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) π-systems have recently attracted attention for use in organic thin-films transistors (OTFTs) and organic photovoltaics (OPVs). This Review article provides an overview of the developments in the past 10 years on the structural design and synthesis of BODIPY-based organic semiconductors and their application in OTFT/OPV devices. The findings summarized and discussed here include the most recent breakthroughs in BODIPYs with record-high charge carrier mobilities and power conversion efficiencies (PCEs). The most up-to-date design rationales and discussions providing a strong understanding of structure-property-function relationships in BODIPY-based semiconductors are presented. Thus, this review is expected to inspire new research for future materials developments/applications in this family of molecules.

Novel BODIPY dyes with electron donor variety for dye-sensitized solar cells

Four D–π–A organic sensitizers (CB1-4), with donor variety were synthesized. CB4, with the advantages of strong donor and suitable connect position presents the broad and intensive absorption, and the best photovoltaic performance with η of 4.28%.

Achieving the highest efficiency using a BODIPY core decorated with dithiafulvalene wings for small molecule based solution-processed organic solar cells

A novel boron dipyrromethene based dye, coded as BODIPY-DTF, decorated with dithiafulvalene wings has been developed for solar cell application.

Novel Dual BODIPY-Carbazole Conjugates with Various Linkers

Four dual BODIPY-carbazole conjugates (BDPa–d, BODIPY is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), with various π bridges, including none, phenyl, thiophene, and furan, were designed and synthesized. The results suggest that the π bridges have significant effect on the thermal, photophysical, and electrochemical properties of the conjugates. BDPc and BDPd, with a five-membered heterocycle as a π bridge possessing more coplanar molecular geometry, exhibit broader and red-shifted absorption with an obvious charge transfer shoulder peak, as well as red-shifted emission. UV-visible absorption spectroscopy and cyclic voltammetry results show that the extension of the π-conjugated system leads to a reduction in the optical gap with a decrease of the LUMO level. All conjugates display remarkable Stokes shifts (107–216 nm) and low fluorescence quantum yields. BDPc and BDPd, which essentially possess broad and intense absorption, and suitable HOMO–LUMO energy levels, are potential candidates for light-harvesting and photovoltaic applications.

Reversal aggregation-induced circular dichroism from axial chirality transfer via self-assembled helical nanowires

Two chiral binaphthyl-based enantiomers, (R/S)-7, can produce gradual reversal AICD signals from solution to aggregation, which can be attributed to axial chirality transfer to self-assembled helical nanowires in aggregation state.

Systematic elongation of thienyl linkers and their effect on optical and electrochemical properties in carbazole–BODIPY donor–acceptor systems

Synthesis, spectral and electrochemical properties of a series of new panchromatic BODIPY donor–acceptor–donor derivatives, comprising carbazole conjugated with systematically elongated framework by thiophene – based linkers were investigated.