scholarly journals Photoconversion Mechanism at the pn-Homojunction Interface in Single Organic Semiconductor

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1727 ◽  
Author(s):  
Ji-Hyun Lee ◽  
Armand Perrot ◽  
Masahiro Hiramoto ◽  
Seiichiro Izawa
Keyword(s):  
Organic Semiconductors ◽  
Organic Semiconductor ◽  
Energy Structure ◽  
Free Charge ◽  
Charge Generation ◽  
Recombination Processes ◽  
Single Host ◽  
Donor Acceptor ◽  
Doping Technique ◽  
Determining Factor

Clarifying critical differences in free charge generation and recombination processes between inorganic and organic semiconductors is important for developing efficient organic photoconversion devices such as solar cells (SCs) and photodetector. In this study, we analyzed the dependence of doping concentration on the photoconversion process at the organic pn-homojunction interface in a single organic semiconductor using the temperature dependence of J–V characteristics and energy structure measurements. Even though the organic pn-homojunction SC devices were fabricated using a single host material and the doping technique resembling an inorganic pn-homojunction, the charge generation and recombination mechanisms are similar to that of conventional donor/acceptor (D/A) type organic SCs; that is, the charge separation happens from localized exciton and charge transfer (CT) state being separated by the energy offset between adjacent molecules, and the recombination happens from localized charge carrier at two adjacent molecules. The determining factor for photoconversion processes is the localized nature of charges in organic semiconductors. The results demonstrated that controlling the delocalization of the charges is important to realize efficient organic photoconversion devices.

scholarly journals Long-lived and disorder-free charge transfer states enable endothermic charge separation in efficient non-fullerene organic solar cells

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Ture F. Hinrichsen ◽  
Christopher C. S. Chan ◽  
Chao Ma ◽  
David Paleček ◽  
Alexander Gillett ◽  
...  
Keyword(s):  
Solar Cells ◽  
Charge Transfer ◽  
Organic Solar Cells ◽  
Charge Separation ◽  
Free Charge ◽  
Charge Generation ◽  
Time Resolved ◽  
Thermodynamic Conditions ◽  
Donor Acceptor ◽  
Interfacial Charge

Abstract Organic solar cells based on non-fullerene acceptors can show high charge generation yields despite near-zero donor–acceptor energy offsets to drive charge separation and overcome the mutual Coulomb attraction between electron and hole. Here, we use time-resolved optical spectroscopy to show that free charges in these systems are generated by thermally activated dissociation of interfacial charge-transfer states that occurs over hundreds of picoseconds at room temperature, three orders of magnitude slower than comparable fullerene-based systems. Upon free electron–hole encounters at later times, both charge-transfer states and emissive excitons are regenerated, thus setting up an equilibrium between excitons, charge-transfer states and free charges. Our results suggest that the formation of long-lived and disorder-free charge-transfer states in these systems enables them to operate closely to quasi-thermodynamic conditions with no requirement for energy offsets to drive interfacial charge separation and achieve suppressed non-radiative recombination.

scholarly journals Rational Design of Donor Acceptor Based Semiconducting Copolymers with High Dielectric Constant

2020 ◽  
Author(s):  
Aiswarya Abhisek Mohapatra ◽  
Yifan Dong ◽  
Puttaraju Boregowda ◽  
Ashutosh Mohanty ◽  
Aditya Sadhanala ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Organic Semiconductors ◽  
Density Functional ◽  
Rational Design ◽  
Dielectric Constants ◽  
Side Chains ◽  
Free Charge ◽  
Coulombic Interaction ◽  
Polymer Backbone ◽  
Donor Acceptor

<div> <div> <div> <p>An efficient photogeneration of free charge carriers has long been recognized as the paramount challenge in organic photovoltaic (OPV) devices. The low dielectric constant organic semiconductors fall short to reduce strong Coulombic interaction of tightly bound exciton and hence lead to a loss mechanism in OPVs due to charge-carrier recombination. To circumvent this problem, we adopt a strategy to enhance the dielectric constant of organic semiconductors by incorporating tetraethyleneglycol (TEG) side-chains. We report synthesis of three new semiconducting copolymers by combining thiophene substituted diketopyrrolopyrrole (TDPP) monomer with three other monomeric units with varying electron donating strength: benzodithiophene (BBT-3TEG-TDPP), TDPP (TDPP-3TEG-TDPP) and naphthalene diimide (PNDITEG-TDPP). BBT-3TEG-TDPP and PNDITEG-TDPP showed highest dielectric constants (~ 5) at 1MHz frequency suggesting efficient contribution of dipolar polarization from TEG side-chains. To understand the electronic contribution of the polymer backbone and the polarity of TEG side-chains, and the resulting enhancement of the dielectric constant, we further performed first-principles density functional theory calculations. Single-component organic solar cells (OSC) fabricated utilizing these polymers resulted in poor performance which is attributed to the absence of free charge generation. Furthermore, transient absorption spectroscopy studies show low exciton diffusion length as observed in donor-acceptor type conjugated polymers. Our results suggest that, the strategy of enhancing dielectric constant with polar side-chains is not sufficient to reduce Coulombic interaction between hole and electron in OSCs. </p> </div> </div> </div>

scholarly journals Free Charge Photogeneration in a Single Component High Photovoltaic Efficiency Organic Semiconductor

2021 ◽  
Author(s):  
Justin Hodgkiss ◽  
Michael Price ◽  
Paul Hume ◽  
Aleksandra Ilina ◽  
Isabella Wagner ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Organic Photovoltaics ◽  
Photovoltaic Cells ◽  
Single Component ◽  
Dielectric Constants ◽  
Organic Photovoltaic ◽  
Free Charge ◽  
Photovoltaic Devices ◽  
Organic Photovoltaic Devices ◽  
Charge Generation

Abstract Organic photovoltaic cells promise cheap, flexible and scalable solar energy. Whereas light directly generates free charges in silicon photovoltaic cells, bound electron and hole pairs known as excitons are understood to be the primary excitations in organic semiconductors due to their low dielectric constants. These excitons must then be split apart at molecular heterojunctions in order to extract current. Recent record efficiency organic photovoltaics utilise the small molecule, Y6, as a key component in the photon-absorbing blend layer. This molecule and its analogues – unlike previous organic semiconductors – have both low band-gaps and high dielectric constants. Here we show that, in a neat film of Y6, these factors lead to intrinsic free charge generation without the need for a molecular heterojunction to split the exciton. We use a suite of intensity-dependent optical spectroscopy measurements to show that a significant (20-90%) fraction of free charges exist in equilibrium with bound states at light intensity equivalent to 1 sun. Rapid bimolecular charge recombination constrains single component Y6 organic photovoltaic devices to low efficiencies, but this recombination is reduced by the introduction of small quantities of donor polymer. Quantum-chemical calculations reveal charge generation pathways through strong coupling between exciton and CT states, and an intermolecular polarisation pattern that drives exciton dissociation. Our results challenge the understanding of how current record efficiency organic photovoltaics operate, and point towards new future possibilities – offering a molecular picture of intrinsic charge generation as a platform to improve charge yields, and renewing the possibility of efficient single-component organic photovoltaic devices.

scholarly journals Rational Design of Donor Acceptor Based Semiconducting Copolymers with High Dielectric Constant

2020 ◽  
Author(s):  
Aiswarya Abhisek Mohapatra ◽  
Yifan Dong ◽  
Puttaraju Boregowda ◽  
Ashutosh Mohanty ◽  
Aditya Sadhanala ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Organic Semiconductors ◽  
Density Functional ◽  
Rational Design ◽  
Dielectric Constants ◽  
Side Chains ◽  
Free Charge ◽  
Coulombic Interaction ◽  
Polymer Backbone ◽  
Donor Acceptor

<div> <div> <div> <p>An efficient photogeneration of free charge carriers has long been recognized as the paramount challenge in organic photovoltaic (OPV) devices. The low dielectric constant organic semiconductors fall short to reduce strong Coulombic interaction of tightly bound exciton and hence lead to a loss mechanism in OPVs due to charge-carrier recombination. To circumvent this problem, we adopt a strategy to enhance the dielectric constant of organic semiconductors by incorporating tetraethyleneglycol (TEG) side-chains. We report synthesis of three new semiconducting copolymers by combining thiophene substituted diketopyrrolopyrrole (TDPP) monomer with three other monomeric units with varying electron donating strength: benzodithiophene (BBT-3TEG-TDPP), TDPP (TDPP-3TEG-TDPP) and naphthalene diimide (PNDITEG-TDPP). BBT-3TEG-TDPP and PNDITEG-TDPP showed highest dielectric constants (~ 5) at 1MHz frequency suggesting efficient contribution of dipolar polarization from TEG side-chains. To understand the electronic contribution of the polymer backbone and the polarity of TEG side-chains, and the resulting enhancement of the dielectric constant, we further performed first-principles density functional theory calculations. Single-component organic solar cells (OSC) fabricated utilizing these polymers resulted in poor performance which is attributed to the absence of free charge generation. Furthermore, transient absorption spectroscopy studies show low exciton diffusion length as observed in donor-acceptor type conjugated polymers. Our results suggest that, the strategy of enhancing dielectric constant with polar side-chains is not sufficient to reduce Coulombic interaction between hole and electron in OSCs. </p> </div> </div> </div>

Engineering dielectric constants in organic semiconductors

2017 ◽  
Vol 5 (15) ◽  
pp. 3736-3747 ◽  
Author(s):  
Ardalan Armin ◽  
Dani M. Stoltzfus ◽  
Jenny E. Donaghey ◽  
Andrew J. Clulow ◽  
Ravi Chandra Raju Nagiri ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Organic Semiconductors ◽  
Organic Semiconductor ◽  
Photovoltaic Device ◽  
Dielectric Constants ◽  
Optical Frequency ◽  
Generation Efficiency ◽  
Charge Generation

An optical-frequency dielectric constant of 4.6 leads to improved charge generation efficiency in an organic semiconductor homojunction photovoltaic device.

Energetic Control of Redox-Active Polymers Towards Safe Organic Bioelectronic Materials

2019 ◽  
Author(s):  
Alexander Giovannitti ◽  
Reem B. Rashid ◽  
Quentin Thiburce ◽  
Bryan D. Paulsen ◽  
Camila Cendra ◽  
...  
Keyword(s):  
Molecular Oxygen ◽  
Organic Semiconductors ◽  
Side Reaction ◽  
Semiconducting Polymers ◽  
Side Reactions ◽  
Redox Active ◽  
Donor Acceptor ◽  
Electrochemical Devices ◽  
Biological Environment ◽  
Device Operation

<p>Avoiding faradaic side reactions during the operation of electrochemical devices is important to enhance the device stability, to achieve low power consumption, and to prevent the formation of reactive side‑products. This is particularly important for bioelectronic devices which are designed to operate in biological systems. While redox‑active materials based on conducting and semiconducting polymers represent an exciting class of materials for bioelectronic devices, they are susceptible to electrochemical side‑reactions with molecular oxygen during device operation. We show that this electrochemical side reaction yields hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), a reactive side‑product, which may be harmful to the local biological environment and may also accelerate device degradation. We report a design strategy for the development of redox-active organic semiconductors based on donor-acceptor copolymers that prevent the formation of H<sub>2</sub>O<sub>2</sub> during device operation. This study elucidates the previously overlooked side-reactions between redox-active conjugated polymers and molecular oxygen in electrochemical devices for bioelectronics, which is critical for the operation of electrolyte‑gated devices in application-relevant environments.</p>

Attaining air stability in high performing n-type phthalocyanine based organic semiconductors

2021 ◽  
Author(s):  
Nathan J Yutronkie ◽  
Benjamin King ◽  
Owen Alfred Melville ◽  
Benoit Hugo Lessard ◽  
Jaclyn L Brusso
Keyword(s):  
Organic Semiconductors ◽  
Organic Semiconductor ◽  
Strong Electron ◽  
Electron Conduction ◽  
High Performing ◽  
Silicon Phthalocyanine

The perfluorinated analogue of silicon phthalocyanine (F2-F16SiPc) has been synthesized as a novel air-stable n-type organic semiconductor. The design of F2-F16SiPc facilitates strong electron conduction through peripheral fluorination that deepens...

Additive-induced Miscibility Regulation and Hierarchical Morphology Enables 17.5% Binary Organic Solar Cells

2021 ◽  
Author(s):  
Jie Lv ◽  
Hua Tang ◽  
Jiaming Huang ◽  
Cenqi Yan ◽  
Kuan Liu ◽  
...  
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Organic Solar Cells ◽  
Organic Solar Cell ◽  
Power Conversion ◽  
Charge Trapping ◽  
Free Charge ◽  
Charge Generation ◽  
Low Charge ◽  
Hierarchical Morphology

Due to the barrierless free charge generation, low charge trapping, and high charge mobilities, the PM6:Y6 organic solar cell (OSC) achieves excellent power conversion efficiency (PCE) of 15.7%. However, the...

scholarly journals Hysteresis Behavior of the Donor–Acceptor-Type Ambipolar Semiconductor for Non-Volatile Memory Applications

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 301
Author(s):  
Young Jin Choi ◽  
Jihyun Kim ◽  
Min Je Kim ◽  
Hwa Sook Ryu ◽  
Han Young Woo ◽  
...  
Keyword(s):  
Organic Semiconductor ◽  
Field Effect ◽  
Field Effect Transistor ◽  
Memory Device ◽  
Non Volatile Memory ◽  
Device Applications ◽  
Donor Acceptor ◽  
Effect Transistor ◽  
Volatile Memory ◽  
Memory Applications

Donor–acceptor-type organic semiconductor molecules are of great interest for potential organic field-effect transistor applications with ambipolar characteristics and non-volatile memory applications. Here, we synthesized an organic semiconductor, PDPPT-TT, and directly utilized it in both field-effect transistor and non-volatile memory applications. As-synthesized PDPPT-TT was simply spin-coated on a substrate for the device fabrications. The PDPPT-TT based field-effect transistor showed ambipolar electrical transfer characteristics. Furthermore, a gold nanoparticle-embedded dielectric layer was used as a charge trapping layer for the non-volatile memory device applications. The non-volatile memory device showed clear memory window formation as applied gate voltage increases, and electrical stability was evaluated by performing retention and cycling tests. In summary, we demonstrate that a donor–acceptor-type organic semiconductor molecule shows great potential for ambipolar field-effect transistors and non-volatile memory device applications as an important class of materials.

Unraveling the Temperature Dependence of Exciton Dissociation and Free Charge Generation in Nonfullerene Organic Solar Cells

Solar RRL ◽  
2021 ◽  
Vol 5 (4) ◽  
pp. 2000789
Author(s):  
Chao Ma ◽  
Christopher C. S. Chan ◽  
Xinhui Zou ◽  
Han Yu ◽  
Jianquan Zhang ◽  
...  
Keyword(s):  
Solar Cells ◽  
Temperature Dependence ◽  
Organic Solar Cells ◽  
Free Charge ◽  
Exciton Dissociation ◽  
Charge Generation
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