Additives treatment is as a very effective strategy to optimize bulk heterojunction (BHJ) morphology. However, the inherent working mechanism of this strategy still lacks systematical investigations ...in non‐fullerene‐acceptors‐based organic solar cells (OSCs). Herein, a series of BHJ and pseudo‐planar heterojunction (PPHJ) OSCs using PM6 and IT‐4F as the electron donor/acceptor pair, are developed to unveil the promoting effect of solvent additive 1, 8‐diiodooctane (DIO) on active layer morphologies and device performance. The study clearly demonstrates that DIO can increase the crystallinity of IT‐4F significantly, while it has less impact on PM6. It is notable that a new efficiency‐determining crystalline balanced factor (CCLpolymer/CCLacceptor) is put forward, indicating that the more balanced CCLpolymer/CCLacceptor results in more balanced charge mobility and much better short‐circuit current densities (Jsc) and fill factors (FF) of OSCs. The PPHJ blend film of PM6/IT‐4F(DIO) exhibits enhanced crystallinity with more balanced CCL and favorable hierarchical distribution morphology, contributing to a champion efficiency of 13.70% with a record Jsc of 20.98 mA cm−2 and a remarkable FF of 75.9%. This work not only reveals the underlying mechanism of DIO caused morphology evolution, but also achieves highly efficient PPHJ OSCs with superior thermal stability by elaborately controlling the morphology of PPHJ film.
The underlying mechanism of 1, 8‐diiodooctane in morphology evolution is unveiled in bulk heterojunction and pseudoplanar heterojunction (PPHJ) organic solar cells (OSCs). A high‐performance PPHJ OSC is achieved by elaborately regulating the PPHJ morphology with a more balanced crystallinity factor. These results offer a deep insight into morphology regulation, which can guide the optimization of device performance.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Strategies for modeling π-conjugated donor molecules for photovoltaic performance in the community of organic solar cells are well renowned in the literature. The recent study is based on the ...modeling of five highly conjugated bicarbazole-based donor molecules (XJ1–XJ5) by the alteration of acetylene-linked 9,9′-bicarbazole triphenylamine (XJ) molecule due to the attachment of five different acceptors through thiophene bridging. DFT simulations were conducted to investigate the geometrical, optoelectronic, and photovoltaic properties by using the CAM-B3LYP/6-31G (d, p) level of theory. FMOs and DOS analysis revealed a reduction of band gap and high charge transfer in the newly designed conjugated systems. TD-DFT method was used to investigate the absorption spectra which revealed that freshly modeled molecules owned higher absorption in the visible region than the reference XJ. The designed molecules showed remarkable photovoltaic characteristics due to the lower transition energies (ΔE), reduced band gap (EG), higher absorption maximum (λm), small binding energies (EB) and high dipole moment. The small values of reorganization energy (RE) for hole and electron possessed high charge mobility. The simulated open-circuit voltage (VOC) with PC61BM acceptor and fill factor (FF) for all the designed systems, in the range 1.78–1.91 V and 0.9253–0.9294 respectively, were found to be greater than reference XJ thereby increasing power conversion efficiency (PCE) of the solar cells. Therefore, all the designed molecules (XJ1–XJ5) are highly recommended for experimentation to fabricate efficient organic solar cells with remarkable photovoltaic applications. The current work is one of the few in-depth investigations in the direction of eco-friendly organic photovoltaics development that will pave the way for researchers to design highly efficient materials for future OSCs by structural engineering.
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•Highly conjugated bicarbazole-based donor molecules were designed.•FMO analysis revealed reduced HOMO-LUMO band gap and high charge transfer after attachment of end group acceptors.•Designed complexes showed maximum absorption in visible regions.•The open-circuit voltage (VOC) of designed molecules and FF exhibited remarkable power conversion efficiency up to 38.93 %
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Intrinsically stretchable polymer semiconductors are highly demanding for flexible electronics. However, it still remains challenging to achieve synergy between intrinsic stretchability and charge ...transport property properly for polymer semiconductors. In this paper, terpolymers are reported as intrinsically stretchable polymeric semiconductors with good ductility and high charge mobility simultaneously by incorporation of non‐centrosymmetric spirocycloalkane‐1,9′‐fluorene (spiro‐fluorene) units into the backbone of diketopyrrolopyrrole (DPP) based conjugated polymers. The results reveal that these terpolymers show obviously high crack onset strains and their tensile moduli are remarkably reduced, by comparing with the parent DPP‐based conjugated polymer without spiro‐fluorene units. They exhibit simultaneously high charge mobilities (>1.0 cm2 V−1 s−1) at 100% strain and even after repeated stretching and releasing cycles for 500 times under 50% strain. The terpolymer P2, in which cyclopropane is linked to the spiro‐fluorene unit, is among the best reported intrinsically stretchable polymer semiconductors with record mobility up to 3.1 cm2 V−1 s−1 at even 150% strain and 1.4 cm2 V−1 s−1 after repeated stretching and releasing cycles for 1000 times.
New intrinsically stretchable polymer semiconductors with good ductility and high charge mobility are designed and investigated by incorporating non‐centrosymmetric spiro‐fluorene units into the backbones of the DPP‐based conjugated polymers. Compared with the parent conjugated polymer, the terpolymers show low moduli and good semiconducting performance both under mechanical deformation and against cyclic strains.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this work, we reported efficient polymer solar cells with balanced hole/electron mobilities tuned by the acceptor content in bulk heterojunction blend films. The photovoltaic cells were fabricated ...with two new wide band-gap D-A polymers PBDDIDT and PBDDIDTT as the donor material. The molecular conformations of new polymers are carefully evaluated by theoretical calculations. The results of photovoltaic studies show that two devices reach their optimal conditions with rich PC71BM content up to 80% in blend films, which is uncommon with most of reported PSCs. The as-cast devices based on PBDDIDT and PBDDIDTT reveal good photovoltaic performance with PCE of 7.04% and 6.40%, respectively. The influence of PC71BM content on photovoltaic properties is further detailed studied by photoluminescence emission spectra, charge mobilities and heterojunction morphology. The results exhibit that more efficient charge transport between donor and acceptor occurs in rich PC71BM blend films. Meanwhile, the hole and electron mobilities are simultaneously enhanced and afford a good balance in rich PC71BM blend films (D/A, 1:4) which is critical for the improvement of current density and fill factors.
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•Acceptor-rich bulk heterojunction polymer solar cells with balanced charge mobilities were reported.•Two new wide band-gap conjugated D/A conjugated materials were deigned as donor materials.•PCE of 7.04% was achieved, ranking one of the best with IDT-based donor polymers.•Balanced hole/electron mobilities of 1.01 were observed in acceptor-rich photovoltaic devices.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This article reviews recent progress on charge generation by doping and its influence on the carrier mobility in organic semiconductors (OSs). The doping induced charge generation efficiency is ...generally low in OSs which was explained by the integer charge transfer model and the hybrid charge transfer model. The ionized dopants formed by charge transfer between hosts and dopants can act as Coulomb traps for mobile charges, and the presence of Coulomb traps in OSs broadens the density of states (DOS) in doped organic films. The Coulomb traps strongly reduce the carrier hopping rate and thereby change the carrier mobility, which was confirmed by experiments in recent years. In order to fully understand the doping mechanism in OSs, further quantitative and systematic analyses of charge transport characteristics must be accomplished.
Electrical doping effects in disordered organic semiconductors are reviewed focusing on the charge generation and carrier mobility. The dopant materials and their charge generation efficiency are introduced firstly. Then the charge transfer processes are described based on two different models, namely the integer charge transfer model and the hybrid charge transfer complex model. The broadening of the Gaussian density‐of‐states upon doping is discussed and experimental results of the charge mobility in doped organic semiconductors are reviewed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Organic solar cells, because of their lightweight, low cost and processing flexibility, are attracting considerable attention in the field of photovoltaic cells. Recently, multiscale computational ...methods have been proposed to study mobilities of organic conjugated polymers that are used in solar cells. In this study, we use a similar multi-step method to investigate charge transport in ordered and orientationally disordered conjugated fluorene and carbazole based organic polymers. The multi-step approach employed in this work involves the use of the density functional theory (DFT), semiempirical (ZINDO) and Monte Carlo (MC) theoretical methods. We compare the one-dimensional (1D) and the three-dimensional (3D) mobility simulation results with experimental values when possible. We find that the simplified multi-step approach used in ordered systems can predict mobility trends that correlate closely with their inter-molecular distances as determined by X-ray experiments. However, the calculated magnitudes of mobilities are two (or more) orders of magnitude higher than the corresponding experimental values for the pristine films. 3D orientationally disordered simulations give decreased mobilities that are roughly of the same order of magnitude as the experimental values. It is known that, currently, numerous approximations are involved even in the most sophisticated multiscale mobility simulations. Our results suggest that, for the purpose of obtaining expediently reasonable mobility values and trends for many conjugated polymers, a simplified multi-step approach can be adequate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Charge-transporting and photoluminescent phenothiazine and carbazole adducts were synthesized and their thermal, optical, photophysical and photoelectrical properties were studied. The materials ...synthesized were found to constitute glasses with glass transition temperatures in the range of 63–78
°C. Their initial weight loss temperatures range from 334 to 362
°C. Steady state and time-resolved fluorescence spectrometry techniques have revealed energy transfer in the adducts of carbazole and phenothiazine and the existence of excimer forming sites in the films of 3-(10-phenothiazinyl)-9-ethylcarbazole and 3-(9-carbazolyl)-9-ethylcarbazole. The electron photoemission spectra of the materials were recorded and the ionization potentials of 5.38–5.87
eV were established. Time-of-flight hole drift mobilities of carbazole twin compound molecularly dispersed in bisphenol
Z polycarbonate (1:2 by weight) approach 2
×
10
−5
cm
2/V
s at high electric field.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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