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Melt-processing of small molecule organic photovoltaics via bulk heterojunction compatibilization.

ABSTRACT: Melt-processing of organic semiconductors (OSCs) is a promising environmentally-friendly technique that can alleviate dependence on toxic chlorinated solvents. While melt-processed single-component OSC devices (e.g. field-effect-transistors) have been demonstrated, multi-component bulk heterojunctions (BHJs) for organic photovoltaics (OPVs) remain a challenge. Herein, we demonstrate a strategy that affords tunable BHJ phase segregation and domain sizes from a single-phase homogeneous melt by employing strongly-crystalline small-molecule OSCs together with a customized molecular compatibilizing (MCP) additive. An optimized photoactive BHJ with 50 wt% MCP achieved a device power conversion efficiency of ca. 1% after melting the active layer at 240 °C (15 min, followed by slow cooling) before deposition of the top electrode. BHJ morphology characterization using atomic force and Kelvin probe microscopy, X-ray diffraction, and photo-luminescence measurements further demonstrate the trade-off between free charge generation and transport with respect to MCP loading in the BHJ. In addition, a functional OPV was also obtained from the melt-processing of dispersed micron-sized solid BHJ particles into a smooth and homogeneous thin-film by using the MCP approach. These results demonstrate that molecular compatibilization is a key prerequisite for further developments towards true solvent-free melt-processed BHJ OPV systems.

SUBMITTER: Rahmanudin A

PROVIDER: S-EPMC5961453 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Melt-processing of small molecule organic photovoltaics <i>via</i> bulk heterojunction compatibilization.

Rahmanudin Aiman A Yao Liang L Jeanbourquin Xavier A XA Liu Yongpeng Y Sekar Arvindh A Ripaud Emilie E Sivula Kevin K

Green chemistry : an international journal and green chemistry resource : GC 20180417 10

Melt-processing of organic semiconductors (OSCs) is a promising environmentally-friendly technique that can alleviate dependence on toxic chlorinated solvents. While melt-processed single-component OSC devices (<i>e.g.</i> field-effect-transistors) have been demonstrated, multi-component bulk heterojunctions (BHJs) for organic photovoltaics (OPVs) remain a challenge. Herein, we demonstrate a strategy that affords tunable BHJ phase segregation and domain sizes from a single-phase homogeneous melt ...[more]

PMID: 29904283

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Project description: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.

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Melt-processing of small molecule organic photovoltaics via bulk heterojunction compatibilization.

Publications

Melt-processing of small molecule organic photovoltaics <i>via</i> bulk heterojunction compatibilization.

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