Predicting Morphology and Processing Strategies for Polymer Solar Cells from X Parameter in High Efficiency Small Molecule Acceptor Based Systems.
Abstract
Polymer solar cells (PSC) are intensely studied and researched due to their potential to providecheap and/or portable electrical power sources. Despite thousands of publications a year, fewstudies have succeeded in determining, let alone predicting and controlling the thermodynamicmetastable morphology limits of the active donor: acceptor layer and understanding how tooptimize fill-factors.Very rapid recent progress indicates that small molecule acceptors (SMAs) will revolutionizePSCs yielding very high efficiency and low voltage loss devices (Voc >1.1 V). Of the continuallygrowing number of SMAs, each could be combined with hundreds of different donor polymers,and high PCEs are only achievable for a small subset of suitable combinations. Current structurefunctionanalysis provides mostly ~post-mortem~ morphology characterization and correlations toprocessing conditions. Such efforts are largely explanatory and not yet predictive. Understandingof the morphology factors that control fill factor is particularly lacking. The weak scatteringcontrast of polymer: SMA blends causes additional barriers in characterizing them extensively byconventional methods and thus hinders establishing morphology-performance relations. Only theresonant soft X-ray scattering tools developed by the PI can analyze such systems uniformly andexpediently.The lack of a reliable and predictive approach to choosing compatible pairs of materialsnecessitated a laborious and wasteful trial-and-error approach in the past that is continued to thisday. Identification of the important material parameters that govern the morphology of PSCdevices is urgently needed so that a rational and simple approach to identify high efficiencycandidate materials systems can be utilized.To overcome these current limitations, we propose to demonstrate that the Flory-Hugginsinteraction parameter chi, which is a measure of the average fundamental molecular interactionsof the SMA or fullerene with the host polymer, is a critical material parameter that quantitativelydetermines the BHJ domain purity variations and thus performance.The objective of the proposed research is to significantly reduce or eliminate trial-and-errorapproaches to molecular design or device fabrication by developing a framework that allows topredict the achievable morphology of PSCs based on measured thermodynamic interactions (~parameters, miscibility) of the constituent materials. This grant will develop the initial frameworkusing model systems, including SMA-based devices that have reached record efficiencies of>12%. Additionally, we will develop and use new methods to determine phase diagrams. The longterm goal, beyond the current scope, is to establish an experimental and theoretical basis forsimulations, such that systems can be designed on the computer before laborious synthesis ordevice optimization is attempted.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 03, 2017
- Source ID
- N000141712204
Entities
People
- Harald Ade
Organizations
- North Carolina State University
- Office of Naval Research
- United States Navy