Understanding the Electronic Structures and Absorption Properties of Porphyrin Sensitizers YD2 and YD2-o-C8 for Dye-Sensitized Solar Cells

Li-Heng Han,Neng-Zhi Jin,Jian-Wu Zhe,Yu-Lin Shen,Zi-Jiang Liu,Ji-Jun Gong,Yu-Hong Chen,Cai-Rong Zhang,Wei Wang

doi:10.3390/ijms141020171

Abstract

The electronic structures and excitation properties of dye sensitizers determine the photon-to-current conversion efficiency of dye sensitized solar cells (DSSCs). In order to understand the different performance of porphyrin dye sensitizers YD2 and YD2-o-C8 in DSSC, their geometries and electronic structures have been studied using density functional theory (DFT), and the electronic absorption properties have been investigated via time-dependent DFT (TDDFT) with polarizable continuum model for solvent effects. The geometrical parameters indicate that YD2 and YD2-o-C8 have similar conjugate length and charge transfer (CT) distance. According to the experimental spectra, the HSE06 functional in TDDFT is the most suitable functional for describing the Q and B absorption bands of porphyrins. The transition configurations and molecular orbital analysis suggest that the diarylamino groups are major chromophores for effective CT excitations (ECTE), and therefore act as electron donor in photon-induced electron injection in DSSCs. The analysis of excited states properties and the free energy changes for electron injection support that the better performance of YD2-o-C8 in DSSCs result from the more excited states with ECTE character and the larger absolute value of free energy change for electron injection.

Highlights

In recent years, dye-sensitized solar cells (DSSCs), as a novel technology for the conversion of solar energy into electricity, have attracted tremendous and continuous research interest because of easy fabrication, lower cost, and relatively higher efficiency comparing to other photovoltaic technology [1,2,3,4,5].It has been found that all of the main components in dye sensitized solar cells (DSSCs), including dye sensitizers, anode, and cathode, as well as electrolyte, can affect the photon-to-current conversion efficiency (PCE)
YD2 consists of a diarylamino group with two hexyl chains attached to the porphyrin ring acting as an electron donor, phenylethynyl group as a part of bridge, the carboxylic acid moiety as an acceptor, and the porphyrin chromophore constitutes the π bridge in this particular donor π-conjugate-bridge acceptor (D-π-A) structure [59]
The quasi-coplanarity between acceptor group and conjugate bridge is favorable for intramolecular charge transfer (IMCT) [64]

Summary

Introduction

Dye-sensitized solar cells (DSSCs), as a novel technology for the conversion of solar energy into electricity, have attracted tremendous and continuous research interest because of easy fabrication, lower cost, and relatively higher efficiency comparing to other photovoltaic technology [1,2,3,4,5]. It has been found that all of the main components in DSSCs, including dye sensitizers, anode, and cathode, as well as electrolyte, can affect the photon-to-current conversion efficiency (PCE). Porphyrins are viewed as one of the more promising dye sensitizers for DSSCs because porphyrin derivatives have better photosynthesis performance, strong UV-visible light absorption, and allow for easy modification/design of their structures [41,42]

Methods

Results

Conclusion