Critical Parameters from Soft X-ray Scattering and Microscopy and Their Relation to Charge Generation and Dynamics in Polymer Solar Cells
Abstract
Abstract/Summary Polymer solar cells (PSC) are intensely studied and researched due to their potential to provide cheap and/or portable electrical power sources. Despite thousands of publications a year, few studies have succeeded in determining, let alone predicting and controlling, the donor/acceptor (D/A) interfacial structural properties and their subsequent effect on charge dynamics and performance in PSCs. The characterization, design, and control of interfaces has been particularly challenging for polymer:fullerene bulk-heterojunction (BHJ) devices, where active layers of polymers and fullerene-derivatives are often quenched into a complex, non-equilibrium 3D morphology by casting a thin film from a common solvent. Neither a comprehensive understanding nor a knowledge-base on how discrete and distributed interfaces can be designed for optimum performance has been achieved. Soft x-ray scattering methods developed by the PI can now for the first time assess molecular ordering relative to the D/A interface in the complex 3D morphology of a BHJ device. In combination with other advanced characterization tools, it is now possible to determine the morphology of polymer solar cells (PSCs) much more completely, and thus study how domain purity as well as molecular orientation at or near bulk heterojunctions (BHJ) determines charge separation and dynamics and device performance. We propose to characterize the morphology of three novel materials systems as completely as possible. This involves 12 polymer:fullerene combinations that have reached efficiency >10% (Henry Yan, HKUST) and derivative materials, as well as fullerene replacements and low-band gap polymers synthesized by Wei You (UNC-CH). The morphology of the Yan donor polymers is very robust, i.e. the domain size and purity depends little on the fullerene used, thus supporting excellent performance for many different fullerene species. It is thus an ideal “host” material to test the suitability of the fullerene replacements to be developed by You. These and follow-up materials represent a large increase in materials combinations that can achieve high efficiency and might be able to push the efficiency to 15% with optimized molecular design, processing and interface engineering. To achieve such improved performance, it is critical to understand how molecule design impacts aggregation and morphology and thus performance. We will also use knowledge gained to extend the spectral absorption of the record devices through IR sensitization through a dye or polymer, or via novel bilayer architecture. One scientific focus will be delineating aggregation and gelation of the solution during casting, how that determines the device morphology and how this is controlled by the chemical structure. The most interesting and promising materials systems and devices will also be characterized by novel spectroscopy methods utilized by Kenan Gondogdu (NCSU) in order to understand the impact of structure and morphology on charge creation and change dynamics, and thus expand our fundamental understanding of PSC function. Through an intensification of established collaborations with You, Yan and Gundogdu a synthesis/structure/charge-dynamics feedback loop will be established that will lead to the discovery of advanced molecular design rules, in turn leading to materials breakthroughs.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512322
Entities
People
- Harald Ade
Organizations
- North Carolina State University
- Office of Naval Research
- United States Navy