Pyran-Squaraine as Photosensitizers for Dye-Sensitized Solar Cells: DFT/TDDFT Study of the Electronic Structures and Absorption Properties

Reda M El-Shishtawy,Shaaban A Elroby,Rifaat H Hilal,Abdullah M Asiri

doi:10.1155/2014/136893

Abstract

In an effort to provide, assess, and evaluate a theoretical approach which enables designing efficient donor-acceptor dye systems, the electronic structure and optical properties of pyran-squaraine as donor-acceptor dyes used in dye-sensitized solar cells were investigated. Ground state properties have been computed at the B3LYP/6-31+G**level of theory. The long-range corrected density functionals CAM-B3LYP, PBEPBE, PBE1PBE (PBE0), and TPSSH with 6-311++G**were employed to examine absorption properties of the studied dyes. In an extensive comparison between experimental results and ab initio benchmark calculations, the TPSSH functional with 6-311++G**basis set was found to be the most appropriate in describing the electronic properties for the studied pyran and squaraine dyes. Natural transition orbitals (NTO), frontier molecular orbitals (FMO), LUMO, HOMO, and energy gaps, of these dyes, have been analyzed to show their effect on the process of electron injection and dye regeneration. Interaction between HOMO and LUMO of pyran and squaraine dyes was investigated to understand the recombination process and charge-transfer process involving these dyes. Additionally, we performed natural bond orbital (NBO) analysis to investigate the role of charge delocalization and hyperconjugative interactions in the stability of the molecule.

Highlights

Dye-sensitized solar cells (DSSCs) have the potential to compete with conventional silicon solar cells, because of their low-cost of manufacturing, great aesthetic features, and potential for indoor and outdoor implementation
The dyes play an important role in gaining higher solar-to-electricity conversion efficiency because the performance of DSSCs strongly depends on the following factors which are the criteria for a good dye sensitizer: (1) wide absorption wavelength in visible to near infrared (IR) region to get most of the sunlight; (2) easy electron injection from the excited state of the dyes to the conduction band of TiO2 due to suitable energy levels (HOMO and LUMO), and (3) good electron transfer from the donor to acceptor [19] that would reduce recombination between holes and electrons
The present study utilizes density functional theory (DFT) methods as very effective means that can provide a systematic approach towards the design of efficient solar energy conversion systems such as sensitizers for dye-sensitized solar cells

Summary

Introduction

Dye-sensitized solar cells (DSSCs) have the potential to compete with conventional silicon solar cells, because of their low-cost of manufacturing, great aesthetic features (color, flexibility, and transparency), and potential for indoor and outdoor implementation. The properties of D-A dyes can be tuned by varying donor, spacer, and acceptor moieties [14,15,16,17,18] From this perspective, the dyes play an important role in gaining higher solar-to-electricity conversion efficiency because the performance of DSSCs strongly depends on the following factors which are the criteria for a good dye sensitizer: (1) wide absorption wavelength in visible to near infrared (IR) region to get most of the sunlight; (2) easy electron injection from the excited state of the dyes to the conduction band of TiO2 due to suitable energy levels (HOMO and LUMO), and (3) good electron transfer from the donor to acceptor [19] that would reduce recombination between holes and electrons

Methods

Results

Conclusion