scholarly journals Ultrafast electron and hole transfer in bulk heterojunctions of low-bandgap polymers

2016 ◽  
Vol 4 (1) ◽  
Author(s):  
Oleg V. Kozlov ◽  
Vlad G. Pavelyev ◽  
Hilde D. de Gier ◽  
Remco W. A. Havenith ◽  
Paul H.M. van Loosdrecht ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Energy Level ◽  
Charge Separation ◽  
Density Functional ◽  
Free Charge ◽  
Charge Generation ◽  
Hole Transfer ◽  
Low Bandgap ◽  
Transfer Processes ◽  
Energy Level Alignment

AbstractIn modern bulk heterojunction (BHJ) organic solar cells, blends of low-bandgap polymer and [70]PCBM acceptor are used in the active layer. In this combination, the polymer absorbs photons from the red and near-IR parts of the solar spectrum, while the blue and near-UV photons are harvested by [70]PCBM. As a result, both electron transfer from polymer to [70]PCBM and hole transfer from [70]PCBM to polymer are of utmost importance in free charge generation and have to be optimized simultaneously. Here we study electron and hole transfer processes in BHJ blends of two low-bandgap polymers, BTT-DPP and PCPDTBT, by ultrafast photoinduced spectroscopy (PIA). By tracking the PIA dynamics, we observed substantially different charge separation pathways in BHJs of the two polymers with [70]PCBM. From the photoinduced anisotropy dynamics, we demonstrated that in the PCPDTBT:[70]PCBM system both electron and hole transfer processes are highly efficient, while in the BTTBPP:[ 70]PCBM electron transfer is blocked due to the unfortunate energy level alignment leaving hole transfer the only pathway to free charge generation. Calculations at the density functional theory level are used to gain more insight into our findings. The presented results highlight the importance of the energy level alignment on the charge separation process.

scholarly journals Effects of co-adsorption on interfacial charge transfer in a quantum dot@dye composite

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
Peng Cui ◽  
Yuan Xue
Keyword(s):  
Electron Transfer ◽  
Charge Transfer ◽  
Quantum Dot ◽  
Charge Separation ◽  
Density Functional ◽  
Co Adsorption ◽  
Hole Transfer ◽  
Interfacial Charge Transfer ◽  
Efficient Charge ◽  
Interfacial Charge

AbstractThe sensitive electronic environment at the quantum dot (QD)–dye interface becomes a roadblock to enhancing the energy conversion efficiency of dye-functionalized quantum dots (QDs). Energy alignments and electronic couplings are the critical factors governing the directions and rates of different charge transfer pathways at the interface, which are tunable by changing the specific linkage groups that connect a dye to the QD surface. The variation of specific anchors changes the binding configurations of a dye on the QD surface. In addition, the presence of a co-adsorbent changes the dipole–dipole and electronic interactions between a QD and a dye, resulting in different electronic environments at the interface. In the present work, we performed density functional theory (DFT)-based calculations to study the different binding configurations of N719 dye on the surface of a Cd33Se33 QD with a co-adsorbent D131 dye. The results revealed that the electronic couplings for electron transfer were greater than for hole transfer when the structure involved isocyanate groups as anchors. Such strong electronic couplings significantly stabilize the occupied states of the dye, pushing them deep inside the valence band of the QD and making hole transfer in these structures thermodynamically unfavourable. When carboxylates were involved as anchors, the electronic couplings for hole transfer were comparable to electron transfer, implying efficient charge separation at the QD–dye interface and reduced electron–hole recombination within the QD. We also found that the electronic couplings for electron transfer were larger than those for back electron transfer, suggesting efficient charge separation in photoexcited QDs. Overall, the current computational study reveals some fundamental aspects of the relationship between the interfacial charge transfer for QD@dye composites and their morphologies which benefit the design of QD-based nanomaterials for photovoltaic applications.

scholarly journals Creation of Hybrid Photoactive Inorganic/Organic Interface Assemblies of Cadmium Oxide mixtures (CdO2/CdO)/Poly-2,2-Bithiophene; Optical and Photoelectrochemical Investigations

2017 ◽  
Vol 9 (4) ◽  
pp. 71
Author(s):  
Kasem K. Kasem ◽  
Henry Worley ◽  
Ashley Lovins
Keyword(s):  
Charge Separation ◽  
Cadmium Oxide ◽  
Equilibrium Mixture ◽  
Organic Polymer ◽  
Aqueous Electrolytes ◽  
Charge Generation ◽  
Transfer Processes ◽  
Organic Interfaces ◽  
Band Alignments ◽  
Induced Charge

Nanoparticles of cadmium peroxide (CdO2) were immobilized in poly 2,2 bithiophene (PBTh) to build photoactive inorganic/organic interfaces (I/O/I). Studies indicated that the CdO2 initially immobilized in the organic polymer partially decomposed to a low band gap CdO. Therefore we refer to this mixture as CdO2/CdO. The CdO2/CdO/PBTh assemblies were subjected to optical and photoelectrochemical investigations in aqueous electrolytes containing acetate, nitrate, or phosphate. The equilibrium mixture of CdO2/CdO influenced the optical conductivity and dielectric contents of the assemblies. Furthermore, O2 played an important role in the charge separation and transfer processes. The effects of an applied magnetic field were investigated and reported. The results were explained on the basis of formation of hybrid sub-bands due to band alignments between the assembly components. The photo-induced charge generation of PBTh was improved by occlusion of CdO2 in the polymer as was evident by the greater photocurrent generated by CdO2/CdO/PBTh than that generated by PBTh.

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 Hole‐Transfer Dependence on Blend Morphology and Energy Level Alignment in Polymer: ITIC Photovoltaic Materials

2017 ◽  
Vol 30 (3) ◽  
pp. 1704263 ◽  
Author(s):  
Nicholas D. Eastham ◽  
Jenna L. Logsdon ◽  
Eric F. Manley ◽  
Thomas J. Aldrich ◽  
Matthew J. Leonardi ◽  
...  
Keyword(s):  
Energy Level ◽  
Hole Transfer ◽  
Photovoltaic Materials ◽  
Blend Morphology ◽  
Energy Level Alignment

scholarly journals A hybrid approach to simulation of electron transfer in complex molecular systems

2013 ◽  
Vol 10 (87) ◽  
pp. 20130415 ◽  
Author(s):  
Tomáš Kubař ◽  
Marcus Elstner
Keyword(s):  
Electron Transfer ◽  
Density Functional ◽  
Degrees Of Freedom ◽  
Hybrid Approach ◽  
Theoretical Description ◽  
Model Systems ◽  
Hole Transfer ◽  
Model Calculations ◽  
Hand Model ◽  
Quantum Mechanical Treatment

Electron transfer (ET) reactions in biomolecular systems represent an important class of processes at the interface of physics, chemistry and biology. The theoretical description of these reactions constitutes a huge challenge because extensive systems require a quantum-mechanical treatment and a broad range of time scales are involved. Thus, only small model systems may be investigated with the modern density functional theory techniques combined with non-adiabatic dynamics algorithms. On the other hand, model calculations based on Marcus's seminal theory describe the ET involving several assumptions that may not always be met. We review a multi-scale method that combines a non-adiabatic propagation scheme and a linear scaling quantum-chemical method with a molecular mechanics force field in such a way that an unbiased description of the dynamics of excess electron is achieved and the number of degrees of freedom is reduced effectively at the same time. ET reactions taking nanoseconds in systems with hundreds of quantum atoms can be simulated, bridging the gap between non-adiabatic ab initio simulations and model approaches such as the Marcus theory. A major recent application is hole transfer in DNA, which represents an archetypal ET reaction in a polarizable medium. Ongoing work focuses on hole transfer in proteins, peptides and organic semi-conductors.

The nature of photogenerated charge separation among different crystal facets of BiVO4studied by density functional theory

2015 ◽  
Vol 17 (36) ◽  
pp. 23503-23510 ◽  
Author(s):  
Taifeng Liu ◽  
Xin Zhou ◽  
Michel Dupuis ◽  
Can Li
Keyword(s):  
Density Functional Theory ◽  
Charge Separation ◽  
Density Functional ◽  
Functional Theory ◽  
Hole Transfer ◽  
Crystal Axis ◽  
Photogenerated Charge Separation

Electron and hole transfer paths along the crystal axis [hkl] and the corresponding facet (hkl).

scholarly journals Efficient Charge Generation Via Hole Transfer in Dilute Organic Donor-Fullerene Blends

2019 ◽  
Author(s):  
Yin Song ◽  
Alexander Schubert ◽  
Xiao Liu ◽  
Srijana Bhandari ◽  
Stephen R. Forrest ◽  
...  
Keyword(s):  
Density Functional ◽  
Electronic Spectroscopy ◽  
Golden Rule ◽  
Charge Generation ◽  
Functional Theory ◽  
Hole Transfer ◽  
Electronic Interactions ◽  
Efficient Charge ◽  
Donor Acceptor ◽  
Via Hole

<p>Efficient organic photovoltaics (OPVs) require broadband charge photogeneration with near-unity quantum yield. This can only be achieved by exploiting all pathways that generate charge. Electron transfer from organic donors to acceptors has been well-studied and is considered the primary path to charge photogeneration in OPVs. In contrast, much less is known about the hole transfer pathway. </p><p>Here we study charge photogeneration in an archetypical system comprising tetraphenyldibenzoperiflanthene: C70 blends using our recently developed multispectral two dimensional electronic spectroscopy (M-2DES), supported by time-dependent density functional theory and fully quantum-mechanical Fermi’s golden rule rate calculations. Our approach identifies in real time two rapid charge transfer pathways that are confirmed through computational analysis. Surprisingly, we find that both electron and hole transfer occur with comparable rates and efficiencies, facilitated by donor-acceptor electronic interactions. Our results highlight the importance of the hole transfer pathway for optimizing the efficiency of OPV devices employing small-molecule heterojunctions.<br></p>

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