Chemistry ETDs

Publication Date

Spring 7-31-2017

Abstract

Current state-of-the-art organic solar cells (OSCs) adopt the strategy of using conjugated polymers or small molecules as donors and fullerene derivatives as acceptors in their active layers. Regarding to the donors of interest, the conjugated polymers and small molecules coupled with heavy metals have been less explored compared to their counterparts. Among various transition metal complexes applied, Pt(II) complexes are unique because of their intrinsic square planar geometries and ability to serve as building blocks for conjugated systems. Furthermore, the heavy metal Pt facilitates the formation of triplet excitons with longer life times through spin-orbital coupling which are of benefit for the OSCs application. However, in order to obtain low bandgap polymers, people are intended to use chromophores with long conjugated length, nevertheless such design will inevitably dilute the spin-orbital coupling effect and finally influence the formation of triplet excitons. Furthermore, the majority of Pt-containing conjugated systems reported so far shared a common feature— they all possessed “dumbbell” shaped structures and were amorphous, leading to poor device performance. In addition, there were few examples reporting the capture of the triplet excitons by the fullerene acceptors in the OSCs since there is a mismatch between the triplet energy state (T1) of the Pt-containing compounds and the LUMO level of fullerene acceptors. As a result, these three intrinsic problems will impede the further development of such a field.

In order to solve these problems, I originally designed and synthesized three novel compounds with unique proprieties named as Bodipy-Pt, Pt-SM and C60+SDS-. Specifically, Bodipy has the advantages of compact size, easy to synthesis and high fluorescence quantum yield which can effectively solve the problem of long conjugated length. While in terms of second problem, the new Pt-SM possessed a “roller-wheel” structural design with increased crystallinity through slip-stack packing; the solar cell efficiency of this compound out-performed all existing Pt-containing materials in organic solar cells. I have further studied the photophysical behavior of the molecule through time-resolved transient absorption spectroscopy as well as DFT calculation. Finally, because of its ionic nature, the LUMO level of C60+SDS- is lower than that of PCBM which serves as a common fullerene acceptor applied in the organic solar cell. Above all, through the measurement of time-resolved transient absorption, I have confirmed the C60+SDS- can capture the triplet exciton of Pt-SM through dynamic quenching since the life-time of triplet exciton has decreased after adding C60+SDS- solution.

Language

English

Keywords

organic solar cells, polymer chemistry, roller-wheel structure, ionic fullerene

Document Type

Dissertation

Degree Name

Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Yang Qin

Second Committee Member

Fu-Sen Liang

Third Committee Member

Ramesh Giri

Fourth Committee Member

Michael Heagy

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