Toward a Rational Design of Poly(2,7-Carbazole) Derivatives for Solar Cells

Abstract

On the basis of theoretical models and calculations, several alternating polymeric structures have been investigated to develop optimized poly(2,7-carbazole) derivatives for solar cell applications. Selected low band gap alternating copolymers have been obtained via a Suzuki coupling reaction. A good correlation between DFT theoretical calculations performed on model compounds and the experimental HOMO, LUMO, and band gap energies of the corresponding polymers has been obtained. This study reveals that the alternating copolymer HOMO energy level is mainly fixed by the carbazole moiety, whereas the LUMO energy level is mainly related to the nature of the electron-withdrawing comonomer. However, solar cell performances are not solely driven by the energy levels of the materials. Clearly, the molecular weight and the overall organization of the polymers are other important key parameters to consider when developing new polymers for solar cells. Preliminary measurements have revealed hole mobilities of about 1 x 10(-3) cm2 x V(-1) x s(-1) and a power conversion efficiency (PCE) up to 3.6%. Further improvements are anticipated through a rational design of new symmetric low band gap poly(2,7-carbazole) derivatives.

On the morphology of polymer‐based photovoltaics

“…The thermal annealing at 70 C, did not significantly change the vertical distribution of the components and the overall crystallinity of the polymer remained relatively constant. The T g of PCDTBT is $130 C, 90 thus, the authors argued that the 70 C annealing brought the active layer above the T g of the PCDTBT due to the presence of residual solvent, and, with time, the trapped solvent diffused out of the active layer without significantly altering the overall morphology. 89 Cyclopentadithiophene-Based Polymer Cyclopentadithiophene-based polymers are another class of promising donor materials.…”

Ternary thiophene–X–thiophene semiconductor building blocks (X=fluorene, carbazole, phenothiazine): Modulating electronic properties and electropolymerization ability by tuning the X core

“…Leclerc et al [29][30][31] developed a class of polymer donors based on carbazole, thiophene and several electron-poor units (including benzothiadiazole) which afforded solar cells with efficiencies as high as 6.1% [32]. The polymer structurally similar to poly{9,9-bisalkylfluorene-2,7-diyl-alt-[4,7-bis(thien-2-yl)-2,1,3-benzothiadiazole]-5'-5"-diyl}, where the fluorene unit is substituted by a 2,7-carbazole unit, exhibits comparable optoelectronic characteristics but an improved hole mobility.…”

Visible to Near-Infrared Light Harvesting in TiO2 Nanotube Array−P3HT Based Heterojunction Solar Cells

“…1,2 The fullerene acceptor absorbs very little light and is primarily used in blends to provide an efficient interface for exciton dissociation. Various efforts toward efficiency improvement in these devices are directed toward the development of low band gap polymers to absorb a broad swathe of the solar spectrum, [3][4][5][6] lowering the molecular energy levels of the semiconducting polymer to enhance the open circuit voltage of the organic solar cells, 1,7 and the control of the blended film morphology for enhanced exciton harvesting. [8][9][10][11][12] In the best performing solid-state dyesensitized solar cells (SS-DSSCs), η ∼ 5%, the only photon absorber is a dye, while the electron and hole transport functions are performed, respectively, by a disordered nanoparticulate TiO 2 network and a transparent small molecule spiro-OMeTAD.…”