Photoinduced Charge Separation Processes Research Articles

Theoretical description of photoinduced electron transfer in donor-acceptor supramolecular complexes based on carbon buckybowls.

Herein, we explore, from a theoretical perspective, the nonradiative photoinduced processes (charge separation and energy transfer) within a family of donor-acceptor supramolecular complexes based on the electron-donor truxene-tetrathiafulvalene (truxTTF) derivative and a series of curved fullerene fragments (buckybowls) of different shapes and sizes (C30H12, C32H12, and C38H14) as electron acceptors that successfully combine with truxTTF via non-covalent interactions. The resulting supramolecular complexes (truxTTF·C30H12, truxTTF·C32H12, and truxTTF·C38H14) undergo charge-separation processes upon photoexcitation through charge-transfer states involving the donor and acceptor units. Despite the not so different size of the buckybowls, they present noticeable differences in the charge-separation efficiency owing to a complex decay post-photoexcitation mechanism involving several low-lying excited states of different natures (local and charge-transfer excitations), all closely spaced in energy. In this intricate scenario, we have adopted a theoretical approach combining electronic structure calculations at (time-dependent) density functional theory, a multistate multifragment diabatization method, the Marcus-Levitch-Jortner semiclassical rate expression, and a kinetic model to estimate the charge separation rate constants of the supramolecular heterodimers. Our outcomes highlight that the efficiency of the photoinduced charge-separation process increases with the extension of the buckybowl backbone. The supramolecular heterodimer with the largest buckybowl (truxTTF·C38H14) displays multiple and efficient electron-transfer pathways, providing a global photoinduced charge separation in the ultrafast time scale in line with the experimental findings. The study reported indicates that modifications in the shape and size of buckybowl systems can give rise to attractive novel acceptors for potential photovoltaic applications.

Control of electronic and exchange coupling by bridge substituents in donor acceptor triads with triptycene bridges.

A series of triads, consisting of a triarylamine electron donor and a perylene diimide electron acceptor which were attached to two different wings of a triptycene bridging unit, was investigated concerning the dynamics of photoinduced charge separation and charge recombination processes with a particular focus on the involved spin-chemical aspects. Attaching electron-donating or electron-withdrawing substituents to the third wing of the triptycene bridge allowed tuning the electron transfer processes. These processes were investigated via fs-transient absorption spectroscopy and ns-transient absorption spectroscopy in an external magnetic field. The resulting magnetic field-dependent decay dynamics were analysed and modelled using the stochastic Liouville equation which yielded rate constants for the charge recombination and the exchange energy. In combination with a diabatic rate theory and Anderson's perturbative treatment of the exchange energy, these data gave a complete set of rate constants for charge separation and charge recombination from which the diverse electronic couplings between the involved states were derived. These couplings depend linearly on the inverse energy of virtual triptycene bridge states which allows tuning the electron transfer dynamics by modifying the triptycene bridge.

(Invited) Theoretical Study on the Environmental Effects on Photoexcited Properties of Donor-Acceptor-Linked Molecules

Photoinduced charge separation process plays important roles in various fields such as natural and artificial photosynthesis, solar cell, and light-emitting diode. Toward an understanding of the molecular mechanism of photoinduced charge separation, we have been studying the excited and charge-separated states of donor-acceptor-linked molecules with theoretical methods such as QM/MM method and molecular dynamics (MD) simulation. In particular, we have focused on the environmental effects on photoexcited properties. In this presentation, we will present recent progress of our research. For example, we will talk about theoretical analysis of acceptor-donor-acceptor type non-fullerene acceptor called TACIC. The excited state of TACIC is known to have a longer lifetime in the film state than in solution. This is in contrast to a similar acceptor-donor-acceptor type non-fullerene acceptor molecule, ITIC, which has a shorter lifetime in the film state than in solution. However, the molecular mechanism is unknown. We analyzed the structures and excited states of the TACIC and ITIC by using quantum chemical calculations and MD simulation. First, it is found that the excited-state potential energy surface of TACIC monomer is similar to that of ITIC monomer, which is consistent with the experimental result that both have similar lifetimes in solution. Next, the packing structure of TACIC in the film state is much different from that of ITIC. Analysis of the excited states of dimer obtained from the film state structure demonstrated that the transition dipole of TACIC dimer is much smaller than that of ITIC dimer. These results could be related to the difference in lifetime of the excited state between TACIC and ITIC in the film state. Further analysis is currently in progress. We will also talk about the photoexcited properties of porphyrin-fullerene linked molecules.

Electron bridging based on ternary AgNPs/MoS2/NaTaO3 heterojunction films enhanced photocatalytic activity

The exceptional cyclic utilization performance of fixed-state thin film photocatalysts has garnered significant interest, yet their industrial application remains constrained by their low photocatalytic efficiency. In this investigation, MoS2/NaTaO3 thin films were synthesized in situ on tantalum substrates utilizing a facile hydrothermal approach. The resulting heterojunction architecture serves to facilitate efficient separation of electron-hole pairs while also notably expanding the photoresponse range. Furthermore, the incorporation of Ag nanoparticles (AgNPs) via photochemical reduction engendered the establishment of Schottky contacts (MoS2-Ag), which considerably expedited the photoinduced charge separation process. Within the context of the ternary system, the construction of electron bridges accelerates the rate of electron transfer. Hence, the designed ternary AgNPs/MoS2/NaTaO3 heterojunction films showed enhanced photocatalytic activity and degraded more than 94.6% of methylene blue (MB) after 50 min of irradiable light. Also, the composite exhibits notable antibacterial efficacy (99.99%) against S. aureus and E. coli owing to the synergistic influence of photo-induced ROS and AgNPs. Moreover, cyclic photocatalytic degradation/sterilization experiments demonstrated the proficient stability of the film.

Synchronistic embedding of oxygen vacancy and Ag nanoparticles into potholed TiO2 nanoparticles-assembly for collaboratively promoting photocatalytic CO2 reduction

Photocatalytic CO2 reduction offers a potential to produce clean and renewable fuels as well as reduce massive emissions of CO2 by utilizing solar energy. The inhibited charge recombination and fertile surface reactive sites play vital roles in determining the photocatalytic performance and products selectivity in CO2 reduction reaction. Herein, the Ag/TiO2-x hybrid by synchronistic introduction of oxygen vacancy and Ag nanoparticles into SiO2 spheres-templated potholed TiO2 assembly with nanoparticles is constructed for photocatalytic CO2 conversion. The Schottky junction between oxygen vacancy TiO2-x and Ag particles provides synergistic enhancement of solar light utilization, photo-induced charge separation and migration process, which is of significance in the promoted CO2 photo-conversion. Indeed, the CH4 yield of oxygen vacancy TiO2-x (1.56 μmol/g/h) is more than 3 times as high as the TiO2 (0.47 μmol/g/h), while the as-synthesized Ag/TiO2-x hybrids show an enhancement of photocatalytic CO2 reduction into CH4 and CO. Among them, the Ag/TiO2-x-10% hybrid has the best photocatalytic performance, and it shows significantly superior CH4 (8.61 μmol/g/h) and CO (2.27 μmol/g/h) yields to that of pure TiO2-x and TiO2.

Structure of the Charge-Transfer State in PM6/Y6 and PM6/Y6:YT Composites Studied by Electron Spin Echo Technique

Nowadays, Y-shaped non-fullerene acceptors become increasingly important in organic photovoltaics (OPV). Their use in binary and ternary bulk heterojunction composites continuously pushes up the efficiency of OPV devices. However, the mechanism of OPV performance enhancement by the third component of a ternary composite is rarely understood. In the present work, pulse EPR technique was used to reveal the similarities and the differences of photoinduced charge separation process in binary PM6/Y6 and ternary PM6/Y6:Y-T composites, where PM6 is polymer donor, Y6 and Y-T are different non-fullerene acceptors. Out-of-phase electron spin echo signal was detected for both composites, which is the signature of the charge-transfer state (CT state) formed at the donor/acceptor interface upon exciton splitting. Nearly identical distribution of the distances between the electron and the hole constituting the CT state was obtained for these composites from the analysis of this signal. In both cases the average electron-hole distance was 3.5 nm. It implies that OPV efficiency increase with Y-T addition is not caused by the increased probability of CT state dissociation followed by free charge generation for PM6/Y6:Y-T composite.

(Invited) Theoretical Study on the Excited and Charge-Separated States of Donor-Acceptor-Linked Molecules

Photoinduced charge separation process plays important roles in various fields such as natural and artificial photosynthesis, solar cell, and light-emitting diode. Toward an understanding of the molecular mechanism of photoinduced charge separation, we have been studying the excited and charge-separated states of donor-acceptor-linked molecules with theoretical methods such as QM/MM method and MD simulation. In this presentation, we will mainly introduce two topics of our research. The first one is porphyrin-fullerene linked molecules. It is experimentally known that the yields of charge-separated states of these molecules is not linear with the bridge length, but reaches a maximum at a specific length. It is also known that the energy of the singlet excited state of this compound is lower in benzonitrile solvent in the following order: local excited state of porphyrin, local excited state of fullerene, and charge separation state. However, by simply using the stable structure of the ground state in the theoretical calculations, the energies of each excited state are in the exact opposite order, and thus the experimental results could not be reproduced. In order to reproduce the experimental results, the structural relaxation of the molecule in the excited state and the response of the solvent are important. However, a simple polarization continuum model of the solvent is insufficient to stabilize the charge separation state. Therefore, we used the QM/MM RWFE-SCF method, which efficiently combines the QM/MM method with MD simulations to optimize the geometry of the solute molecule (QM region) with quantum chemical calculations including the effects of the thermal fluctuations of the surrounding environment such as the solvent molecules (MM region) treated by the molecular mechanics force field. The energy differences calculated with the QM/MM RWFE-SCF method are in good agreement with the experimental results. The charge-separated state is greatly stabilized by solvent molecules due to the large dipole moment. The next topic is acceptor-donor-acceptor type non-fullerene acceptor called TACIC. The excited state of TACIC is known to have a longer lifetime in the film state than in solution. This is in contrast to a similar non-fullerene acceptor molecule, ITIC, which has a shorter lifetime in the film state. However, the molecular mechanism is unknown. We analyzed the structures and excited states of the TACIC and ITIC by using quantum chemical calculations and MD simulation. It is found that the packing structure of TACIC in the film state is much different from that of ITIC, which could be related to the difference in lifetime of the excited state. Further analysis is currently in progress.

Amending charge separation and migration in TiO2 nanosheet via Au nanoparticles ensemble and its synergy in photoelectrocatalytic methanol oxidation

In this report, the preparation of an ensemble of hydrothermally synthesized TiO 2 nanosheets with Au nanoparticles (TiO 2 NSs-Au NPs) and their photoelectrocatalytic methanol oxidation behavior are accounted. The absorption spectral studies confirmed the successful emergence of Au NPs on TiO 2 NSs ensemble and the existence of Au NPs broadened the light absorption to the visible light spectrum. The crystalline and structural complexity analysis confirms the anatase TiO 2 as a major product in this synthesis. Morphology studies revealed the formation of 2 dimensional TiO 2 NSs with chemically deposited Au NPs at the TiO 2 surface and it was further confirmed by STEM-HAADF-EDS mapping studies. The ITO/TiO 2 NSs-Au modified photoelectrode showed a synergistic catalytic response towards photoelectrocatalytic methanol oxidation than the ITO/TiO 2 NSs electrode. Among them, TiO 2 NSs with 1 mM Au NPs deposited composite (TiO 2 NSs-Au (1)) showed 2-fold higher photocurrent for methanol oxidation than their pristine TiO 2 NSs. The deposited of Au NPs in TiO 2 NSs-Au nanocomposites facilitates the photoinduced charge separation and charge migration processes. Coherently the charge recombination process diminished in the TiO 2 NSs-Au nanocomposite materials. The best synergistic photoelectrocatalytic methanol oxidation reaction at the ITO/TiO 2 NSs-Au (1) modified electrode was achieved via extended visible light absorption with Schottky barrier induced enhancement of interfacial electron transfer process. • Two-dimensional TiO 2 nanosheets modified with Au NPs (TiO 2 NSs-Au). • The ITO/TiO 2 NSs-Au modified electrodes show a synergistic catalytic response. • ITO/TiO 2 NSs-Au shows enhanced photoelectrocatalytic methanol oxidation. • The Schottky barrier enhances the interfacial electron transfer process.

Mixed-metal Zr/Ti MIL-173 porphyrinic metal–organic frameworks as efficient photocatalysts towards solar-driven overall water splitting

A hydrolytically stable metal–organic framework containing Ti(iv) and porphyrinic linkers allows a photoinduced charge separation process for the photocatalytic overall water splitting reaction.

The Carbene Cannibal: Photoinduced Symmetry-Breaking Charge Separation in an Fe(III) N-Heterocyclic Carbene.

Photoinduced symmetry-breaking charge separation (SB-CS) processes offer the possibility of harvesting solar energy by electron transfer between identical molecules. Here, we present the first case of direct observation of bimolecular SB-CS in a transition metal complex, [FeIIIL2](PF6) (L = [phenyl(tris(3-methylimidazol-1-ylidene))borate]−). Photoexcitation of the complex in the visible region results in the formation of a doublet ligand-to-metal charge transfer (2LMCT) excited state (E0–0 = 2.13 eV), which readily reacts with the doublet ground state to generate charge separated products, [FeIIL2] and [FeIVL2]2+, with a measurable cage escape yield. Known spectral signatures allow for unambiguous identification of the products, whose formation and recombination are monitored with transient absorption spectroscopy. The unusual energetic landscape of [FeIIIL2]+, as reflected in its ground and excited state reduction potentials, results in SB-CS being intrinsically exergonic (ΔGCS° ∼ −0.7 eV). This is in contrast to most systems investigated in the literature, where ΔGCS° is close to zero, and the charge transfer driven primarily by solvation effects. The study is therefore illustrative for the utilization of the rich redox chemistry accessible in transition metal complexes for the realization of SB-CS.

(Invited) Toward a Molecular Understanding of Photoinduced Charge Separation Process in Organic Solar Cells with Computational Approaches

Photoinduced charge separation (CS) process plays important roles in various fields such as natural and artificial photosynthesis, solar cell, and light-emitting diode. To investigate the photoinduced CS process theoretically, the CS state is often regarded as “static exciton” and described by several parameters such as free energy difference and electronic coupling between initial and final states according to Marcus theory. However, dynamical effects such as nuclear motions and spin-orbit coupling (SOC) are recently being recognized as important factors for controlling the CS efficiency. Therefore, the CS state should be considered as “dynamic exciton.” To analyze the dynamic exciton theoretically, we need to treat the photoexcited reaction dynamics quantum mechanically, where the locally excited and CS states, electronic coupling and SOC dynamically fluctuates. In addition, surrounding environment such as solvent are also important and required to be explicitly considered because the charge distribution of CS state is much different from that of initial state. It is impossible to treat all the systems including surroundings quantum mechanically. Therefore, combined quantum mechanical and molecular mechanical (QM/MM) method, in which an important subsystem is described quantum mechanically whereas the other surrounding is treated by molecular mechanics force field, is an essential tool. However, even the QM/MM method still requires large computational cost for the analysis of dynamic exciton because the calculation time of excited state is much longer than that of ground state. To overcome this difficulty, we have been developing several methods combining the QM/MM method and molecular dynamics simulation efficiently. In this presentation, we will show several applications toward a molecular understanding of photoinduced CS process in organic solar cells.

Binuclear Mn oxo complex as a self-contained photocatalyst in water-splitting cycle: Role of additional Mn oxides as a buffer of electrons and protons.

We theoretically propose a photoinduced water-splitting cycle catalyzed by a binuclear Mn oxo complex. In our "bottom-up approach" to this problem, we once proposed a working minimal model of water-splitting cycle in terms of a mononuclear Mn oxo complex as a catalyst along with water clusters [K. Yamamoto and K. Takatsuka, Phys. Chem. Chem. Phys. 20, 6708 (2018)]. However, this catalyst is not self-contained in that the cycle additionally needs buffering molecules for electrons and protons in order to reload the Mn complex with electrons and protons, which are lost by photoinduced charge separation processes. We here show that a binuclear Mn oxo complex works as a self-contained photocatalyst without further assistant of additional reagents and propose another catalytic cycle in terms of this photocatalyst. Besides charge separation and proton relay transfer, the proposed cycle consists of other fundamental chemical dynamics including electron-proton reloading, radical relay-transfer, and Mn reduction. The feasibility of the present water-splitting cycle is examined by means of full dimensional nonadiabatic electron-wavepacket dynamics based on multireference electronic wavefunctions and energy profiles estimated with rather accurate quantum chemical methods for all the metastable states appearing in the cycle.

Photocatalytic Water Splitting Cycle in a Dye-Catalyst Supramolecular Complex: Ab Initio Molecular Dynamics Simulations

A dye-sensitized photoelectrochemical cell (DS-PEC) is a promising device for direct conversion of solar energy into fuel. The basic idea, inspired by natural photosynthesis, is to couple the photoinduced charge separation process to catalytic water splitting. The photo-oxidized dye coupled to a water oxidation catalyst (WOC) should exert a thermodynamic driving force for the catalytic cycle, while water provides the electrons for regenerating the oxidized dye. These conditions impose specific energetic constraints on the molecular components of the photoanode in the DS-PEC. Here, we consider a supramolecular complex integrating a mononuclear Ru-based WOC with a fully organic naphthalene-diimide (NDI) dye that is able to perform fast photoinduced electron injection into the conduction band of the titanium-dioxide semiconductor anode. By means of constrained ab initio molecular dynamics simulations in explicit water solvent, it is shown that the oxidized NDI provides enough driving force for the whole photocatalytic water splitting cycle. The results provide strong evidence for the significant role of spin alignment and solvent rearrangement in facilitating the proton-coupled electron transfer processes. The predicted activation free energy barriers confirm that the O–O bond formation is the rate-limiting step. Our results expand the current understanding of the photocatalytic water oxidation mechanism and provide guidelines for the optimization of high-performance DS-PEC devices.

Synthesis, photophysical and electrochemical properties of a new star-shaped molecule with a 1,3,5-triethynylbenzene core and diketopyrrolopyrrole arms.

A new star-shaped small molecule BDPP-1 based on 1,3,5-triethynylbenzene as a core and diketopyrrolopyrrole (DPP) as rigid arms have been successfully designed and synthesized. The thermal stability, photophysical and electrochemical properties were explored. The synthesized star-shaped small molecule BDPP-1 exhibited excellent solubility, high thermal stability, broad and strong absorption, narrow band gap and appropriate molecular levels. Moreover, the photoinduced charge separation process between the synthesized donor and acceptor PC61BM was evaluated by the fluorescence quenching experiment, revealing that the donor material BDPP-1 possessed efficient photoinduced charge separation performance. These detailed investigations on the structure-property relationship of the novel star-shaped molecule revealed that BDPP-1 is a prospective candidate as a donor material for organic photovoltaic materials.

The synthesis and properties of linear A–π–D–π–A type organic small molecule containing diketopyrrolopyrrole terminal units

A novel linear A-π-D-π-A-type organic small molecule Ph2(PDPP)2 consisting diketopyrrolopyrrole (DPP) as acceptor unit, biphenylene as donor unit and acetylene unit as π-linkage has been successfully designed and synthesized. Its corresponding thermal, photophysical and electrochemical properties as well as the photoinduced charge-separation process were investigated. Ph2(PDPP)2 exhibits high thermal stability and it can be soluble in common organic solvents such as chloroform and tetrahydrofuran. The photophysical properties show that DPP2Ph2 harvests sunlight over the entire visible spectrum range in the thin-film state (300–800nm). DPP2Ph2 has lower band gaps and appropriate energy levels to satisfy the requirement of solution-processable organic solar cells. The efficient photoinduced charge separation process was clearly observed between DPP2Ph2 with PC61BM and the Ksv value was found to be as high as 2.13×104M−1. Therefore, these excellent properties demonstrate that the designed A-π-D-π-A-type small molecule Ph2(PDPP)2 is the prospective candidate as donor material for organic photovoltaic material.

Photoinduced surface voltage mapping study for large perovskite single crystals

Using a series of illumination sources, including white light (tungsten-halogen lamp), 445-nm, 532-nm, 635-nm, and 730-nm lasers, the surface photovoltage (SPV) images were mapped for centimeter-sized CH3NH3PbX3 (X = Cl, Br, I) perovskite single crystals using Kelvin probe force microscopy. The significant SPV signals were observed to be wavelength-dependent. We attribute the appreciable SPV to the built-in electric field in the space charge region. This study shines light into the understanding of photoinduced charge generation and separation processes at nanoscale to help advance the development of perovskite solar cells, optoelectronics, laser, photodetector, and light-emitting diode (LED).

Charge Separation: Improving Charge Separation across a Hybrid Oxide/Polymer Interface by Cs Doping of the Metal Oxide (Adv. Mater. Interfaces 7/2016)

In article number 1500616, Y. Sevinchan and co-workers investigate the photo-induced charge separation process at a metal oxide/polymer interface. Incorporation of a Cs dopant in the metal oxide reduces the density of gap states at the oxide surface, thus lowering the number of bound charge pairs formed at the organic/inorganic interface. This reduction in interfacial trapping suppresses the recombination and enhances the photocurrent in hybrid photovoltaic cells.

Theoretical estimation of the rate of photoinduced charge transfer reactions in triphenylamine C60 donor-acceptor conjugate.

Fullerene-based molecular heterojunctions such as the [6,6]-pyrrolidine-C60 donor-acceptor conjugate containing triphenylamine (TPA) are potential materials for high-efficient dye-sensitized solar cells. In this work, we estimate the rate constants for the photoinduced charge separation and charge recombination processes in TPA-C60 using the unrestricted and time-dependent DFT methods. Different schemes are applied to evaluate excited state properties and electron transfer parameters (reorganization energies, electronic couplings, and Gibbs energies). The use of open-shell singlet or triplet states, several density functionals, and continuum solvation models is discussed. Strengths and limitations of the computational approaches are highlighted. The present benchmark study provides an overview of the expected performance of DFT-based methodologies in the description of photoinduced charge transfer reactions in fullerene heterojunctions. © 2016 Wiley Periodicals, Inc.

Interfacial carrier dynamics in PbS-ZnO light harvesting assemblies and their potential implication in photovoltaic/ photocatalysis application

In many cases light harvesting nanomaterials are commonly applied as photovoltaics as well as photocatalyst materials. However, such a dual use depends critically on the charge dynamics across the involved nanostructured interface. Here, we have investigated PbS-ZnO light harvesting assemblies (LHAs) that can lead to efficient photovoltaics. In contrast, their photocatalytic properties remain poor. We demonstrate that fundamental, ultrafast photoinduced charge separation and charge recombination processes at the semiconductor-semiconductor interface are key factors for the dual application of LHAs. In the course of our investigation we have synthesized and characterized the PbS-ZnO LHAs using high resolution transmission electron microscopy (HRTEM) and UV–vis absorption spectroscopy. Picosecond-resolved photoluminescence study has been employed to investigate the ultrafast interfacial charge transfer dynamics within the LHA upon photoexcitation. Picosecond-resolved PL-quenching of ZnO nanoparticles (NPs) show Förster Resonance Energy Transfer (FRET) from donor ZnO NPs to the acceptor PbS quantum dots (QDs) and the latter has been employed to confirm the proximity of PbS to the host ZnO with molecular resolution. The photocatalytic activity of PbS−ZnO LHAs is probed by monitoring the photoreduction of the test contaminant methylene blue (MB) and correlated with ultrafast spectroscopic studies on LHAs. This allows a conclusion on the role of ultrafast electron shuttling across the interface in making the electron unavailable for a reduction of MB. The prospective use of the LHAs in photovoltaics is investigated by photoelectrochemical studies where working electrodes of PbS-ZnO LHAs show higher photocurrents than that of bare ZnO NPs. This clearly indicates that the presence of an Indiumtinoxide (ITO) substrate provides directionality to the shuttling electrons at the PbS-ZnO interface. The exploration of interfacial carrier dynamics in PbS-ZnO LHAs will be helpful in improving the design and efficiency of future solar energy harvesting devices.

Heterodimers formed through a partial anionic exchange process: scanning tunneling spectroscopy to monitor bands across the junction vis-à-vis photoinduced charge separation.

We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk-heterojunction solar cells based on the nanostructures in a polymer matrix.