Structural and electronic properties of the P3HT–PCBM dimer: A theoretical Study

Exploring fullerene derivatives for optoelectronic applications: synthesis and characterization study

In this study, we conducted a comprehensive investigation of newly synthesized fullerene derivatives developed for potential application in perovskite solar cells (PSCs). We explored three novel dihydrofuran-fused C60 fullerene derivatives (13, 14, and 15) that were specifically designed to enhance solubility and interaction with the substrate, fluorine-doped tin oxide (FTO). A comparative analysis was performed, with reference to the widely used phenyl-C61-butyric acid methyl ester (PCBM) and compound 12, from which 13, 14, and 15 are derived, to assess the impact of sugar units on materials properties. The synthesized compounds demonstrated significant solubility in common organic solvents, a critical factor in their potential application in wet-processed PSCs. Our investigation included electrochemical property analysis, thin film deposition, surface characterization, and electrochemical impedance spectroscopy (EIS). EIS measurements unveiled key insights into charge transfer properties at the electrode/electrolyte interface, making the compounds attractive candidates for electron transport layers (ETLs) in PSCs.

Modeling the Effect of Disorder in the Two-Dimensional Electronic Spectroscopy of Poly-3-hexyltiophene in an Organic Photovoltaic Blend: A Combined Quantum/Classical Approach

We introduce a first-principles model of the 12-mer poly-3-hexyltiophene (P3HT) polymer system in the realistic description of an organic photovoltaic blend environment. We combine Molecular Dynamics (MD) simulations of a thin-film blend of P3HT and phenyl-C61-butyric acid methyl ester (PCBM) to model the interactions with a fluctuating environment with Time-Dependent Density Functional Theory (TDDFT) calculations to parametrize the effect of the torsional flexibility in the polymer and construct an exciton-type Hamiltonian that describes the photoexcitation of the polymer. This allows us to reveal the presence of different flexibility patterns governed by the torsional angles along the polymer chain which, in the interacting fluctuating environment, control the broadening of the spectral observables. We identify the origin of the homogeneous and inhomogeneous line shape of the simulated optical signals. This is paramount to decipher the spectroscopic nature of the ultrafast electron-transfer process occurring in organic photovoltaic (OPV) materials.

Effect of static external electric field on bulk and interfaces in organic solar cell systems: A density-functional-theory-based study

In this work, a detailed comparison of optical and electronic properties in bulk and interfaces of well-known organic semiconductor systems in presence of an external electric field is reported. We have used density functional theory (DFT) to model organic solar cell systems. The study promotes a deeper understanding of the connection between the chemical structures and the optical and electronic properties in the well-known organic solar cell systems based on thiophene and fullerene polymers. We have performed a vibration-mode analysis by simulating Raman spectra in presence of external electric fields. Time-dependent DFT has been used to investigate the effect of an external electric field on excited state properties. The charge-transfer rate controlled by the external electric field has been quantitatively extracted using the simulated excited state dipole moment, Gibbs free energy, and Marcus theory. Our results provide a detailed characterization of the effect of the external electric field on the neat polymers (bulk) and on the donor-acceptor heterojunctions (interfaces) in organic solar cell systems. This theoretical approach not only helps to understand the effect of an external field on bulk and interfaces in organic semiconductors, but it also supports the design of novel devices.

Optoelectronic Properties of C60 and C70 Fullerene Derivatives: Designing and Evaluating Novel Candidates for Efficient P3HT Polymer Solar Cells

Ten novel fullerene-derivatives (FDs) of C60 and C70 had been designed as acceptor for polymer solar cell (PSC) by employing the quantitative structure-property relationship (QSPR) model, which was developed strategically with a reasonably big pool of experimental power conversion efficiency (PCE) data. The QSPR model was checked and validated with stringent parameter and reliability of predicted PCE values of all designed FDs. They were assessed by the applicability domain (AD) and process randomization test. The predicted PCE of FDs range from 7.96 to 23.01. The obtained encouraging results led us to the additional theoretical analysis of the energetics and UV-Vis spectra of isolated dyes employing Density functional theory (DFT) and Time-dependent-DFT (TD-DFT) calculations using PBE/6-31G(d,p) and CAM-B3LYP/6-311G(d,p) level calculations, respectively. The FD4 is the best C60-derivatives candidates for PSCs as it has the lowest exciton binding energy, up-shifted lowest unoccupied molecular orbital (LUMO) energy level to increase open-circuit voltage (VOC) and strong absorption in the UV region. In case of C70-derivatives, FD7 is potential candidate for future PSCs due to its strong absorption in UV-Vis region and lower exciton binding energy with higher VOC. Our optoelectronic results strongly support the developed QSPR model equation. Analyzing QSPR model and optoelectronic parameters, we concluded that the FD1, FD2, FD4, and FD10 are the most potential candidates for acceptor fragment of fullerene-based PSC. The outcomes of tactical molecular design followed by the investigation of optoelectronic features are suggested to be employed as a significant resource for the synthesis of FDs as an acceptor of PSCs.

The Driving Force of Photoinduced Charge Separation in Metal-Cluster-Encapsulated Triphenylamine-[80]fullerenes

Understanding photoinduced charge separation in fullerene-based dye-sensitized solar cells is crucial for the development of photovoltaic devices. We investigate here how the driving force of the charge separation process in conjugates of M@C₈₀ (M=Sc₃ N, Sc₃ CH, Sc₃ NC, Sc₄ O₂ , and Sc₄ O₃ ) with triphenylamine (TPA) depends on the nature of the metal cluster. Both singlet and triplet excited-state electron-transfer reactions are considered. These results based on TD-DFT calculations demonstrate that the driving force of charge separation in TPA-M@C₈₀ can be tuned well by varying the structure of the metal cluster encapsulated inside the fullerene cage.

Ultrafast decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells

All-organic-based photovoltaic solar cells have attracted considerable attention because of their low-cost processing and short energy payback time. In such systems the primary dissociation of an optical excitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient, but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitation spectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decay of photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The two-dimensional photocurrent spectra are interpreted by introducing a theoretical model for the description of the coupling of the electronic states of the system to an external environment and to the applied laser fields. The experimental data show no cross-peaks in the twodimensional photocurrent spectra, as predicted by the model for coherence times between the exciton and the photocurrent producing states of 20 fs or less.

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.