Fullerene-Based Photoactive Layers for Heterojunction Solar Cells: Structure, Absorption Spectra and Charge Transfer Process.

Yuanzuo Li,Dawei Qi,Peng Song,Fengcai Ma

doi:10.3390/ma8010042

Yuanzuo Li, Dawei Qi + Show 2 more

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https://doi.org/10.3390/ma8010042

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Abstract

The electronic structure and optical absorption spectra of polymer APFO3, [70]PCBM/APFO3 and [60]PCBM/APFO3, were studied with density functional theory (DFT), and the vertical excitation energies were calculated within the framework of the time-dependent DFT (TD-DFT). Visualized charge difference density analysis can be used to label the charge density redistribution for individual fullerene and fullerene/polymer complexes. The results of current work indicate that there is a difference between [60]PCBM and [70]PCBM, and a new charge transfer process is observed. Meanwhile, for the fullerene/polymer complex, all calculations of the twenty excited states were analyzed to reveal all possible charge transfer processes in depth. We also estimated the electronic coupling matrix, reorganization and Gibbs free energy to further calculate the rates of the charge transfer and the recombination. Our results give a clear picture of the structure, absorption spectra, charge transfer (CT) process and its influencing factors, and provide a theoretical guideline for designing further photoactive layers of solar cells.

Highlights

Organic heterojunction photovoltaic devices have received increasing scientific attention owing to their flexibility, ease of processing, potentially low cost and the long-term sustainability advantages of organics [1,2,3,4], as well as being viewed as promising alternatives for established silicon based systems.For a heterojunction solar cell, the active layer is sandwiched between a transparent indium tin oxide (ITO) anode and a low-work-function metal cathode, comprised of a conjugated polymer as donor (D) and a fullerene derivative as acceptor (A)
The LUMOs of the binary system are closed to that of fullerenes, their HOMOs verge on HOMOs of APFO3, which leads to charge transfer controlling by transition from HOMO to LUMO and can take place from
We have theoretically studied the optical physics characteristics of individual APFO3, fullerene

Summary

Introduction

Organic heterojunction photovoltaic devices have received increasing scientific attention owing to their flexibility, ease of processing, potentially low cost and the long-term sustainability advantages of organics [1,2,3,4], as well as being viewed as promising alternatives for established silicon based systems.For a heterojunction solar cell, the active layer is sandwiched between a transparent indium tin oxide (ITO) anode and a low-work-function metal cathode, comprised of a conjugated polymer as donor (D) and a fullerene derivative as acceptor (A). The candidates of an electron transfer system with high-efficiency are covalently linked donor and acceptor moieties; for example, some photosensitizing electron donors such as porphyrin, phthalocyanine and ruthenium phthalocyanine, were covalently linked to fullerene [7,8,9]. Another approach is a mixture of fullerene with an electron donor, such as poly(3-hexylthiophene) (P3HT): [60]PCBM, Poly(p-phenylene vinylene) (PPV): [60]PCBM, metallophthalocyanine: fullerene [10,11,12,13,14], etc

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