Determination of Nanomaterial Energy Levels for Organic Photovoltaics by Cyclic Voltammetry
- PDF / 402,333 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 178 Views
1031-H09-54
Determination of Nanomaterial Energy Levels for Organic Photovoltaics by Cyclic Voltammetry Roberta Ann DiLeo1, Annick Anctil2, Brian Landi1, Cory Cress2, and Ryne P Raffaelle1 1 Rochester Institute of Technology, Rochester, NY, 14623 2 Microsystems Engineering, Rochester Institute of Technology, Rochester, NY, 14623 ABSTRACT A wide variety of nanomaterials and associated nanomaterial/polymer composites are being developed in an effort to produce higher efficiency organic solar cells. This development requires a fundamental understanding of the energy levels for the individual materials, and their composites, to enable device designs which posess appropriate energy level matching. Cyclic voltammetry (CV) allows for the determination of the band gaps (Eg) and energy levels of these various nanomaterials and composites by measuring their oxidation and reduction potentials. These potentials correspond to a given material’s ionization potential (IP) and electron affinity (EA), respectively. The results for the EA, IP, and Eg have been determined by CV for derivatized fullerenes and CdSe quantum dots (QD), measured in isolation, and in conjugated polymer composites with MEH-PPV. In addition, CV measurements conducted under dark and illuminated conditions were used to investigate the relationship between energy levels within the composites. INTRODUCTION The rapidly growing field of organic photovoltaics (PV) is pushing the limits of achievable efficiencies with conventional materials [1, 2]. The development of high efficiency devices requires an assembly of compatible materials which support photon absorption, exciton diffusion, exciton dissociation, and carrier transport [3]. Choice of suitable materials and their energy level alignments are critical to the development of efficient devices. The enhancement of photon absorption in a device can be accomplished by selecting materials with appropriate band gaps to absorb the solar spectrum. It is also important to minimize recombination sites within the bulk junction; this can be done by avoiding materials which will cause traps due to their unsuitable energy level alignment. Cyclic voltammetry (CV) is a characterization technique that offers the capabilities of probing these important material properties. It is possible to calculate a material’s ionization potential (IP) and electron affinity (EA), which correspond to valence states and conduction states, respectively, using CV. Electrochemical CV measurements can be used to determine these potentials by measuring the voltages at which the material undergoes reduction or oxidation with respect to a reference electrode. These values can be used to calculate the EA and IP of a material as explained by Kucur et al. [4]:
EA = −( Ered + ∆Evacuum,electrode)
IP = −( Eox + ∆Evacuum ,electrode )
(1)
(2) The band gap (Eg) can be obtained by taking the energy difference of the EA and IP.
There have been several reports on the cyclic voltammetry of nanomaterials and polymers commonly used in organic photovoltaics [5-
Data Loading...
