Center for Functional Nanomaterials Seminar

"Rational Design of High Performance Polymers for Solar Cells: Past, Current and Future"

Presented by Wei You, University of North Carolina, Chapel Hill

Monday, January 23, 2012, 9:30 am — Bldg. 735 - Conf Rm A

The past: The bulk heterojunction (BHJ) organic photovoltaic cells of regioregular poly(3-hexylthiophene) (RR-P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) represent one of the most successful systems with reproducible efficiencies approaching 5% after careful optimization. However, with a fixed band gap of 1.9 eV, P3HT can only harvest a small portion of the solar spectrum (maximum 22.4%). Therefore low band gap polymers for better light harvesting have been intensively pursued in recent years. Though impressive progresses have been made, the outstanding question remains: how to rationally design ideal polymers to approach 10% efficiency and beyond?

The current: I will summarize the design criteria for “ideal” polymers to be used with PCBM to further improve the efficiency of BHJ photovoltaic devices. Specifically, I will focus on three main topics: (a) design of new conjugated backbone to control the band gap and energy levels; (b) the significant influence of “trivial” side chains; (c) the impact of substituents such as F. A number of new polymers will be discussed in detail to elaborate these topics. A design motif has been proposed, which successfully produced polymers that demonstrated over 7% efficiency in BHJ devices.

The future: How can we reach an even higher efficiency of BHJ solar cells? To answer this question, I will further discuss a few outstanding issues, and make recommendations.

Hosted by: Barney Grubbs

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