Modeling Ultrafast Exciton Migration within the Electron Donor Domains of Bulk Heterojunction Organic Photovoltaics

Abstract

Recent experimental studies revealed that charge carriers harvested by bulk heterojunction organic photovoltaics can be collected on ultrafast time scales. To investigate ultrafast exciton mobility, we construct simple, nonatomistic models of a common polymeric electron donor material. We first explore the relationship between the magnitude of energetic noise in the model Hamiltonian and the spatial extent of resulting eigenstates. We then employ a quantum master equation approach to simulate migration of chromophore-localized initial excited states. Excitons initially localized on a single chromophore at the center of the model delocalize down polymer chains and across pi-stacked chromophores through a coherent, wavelike mechanism during the first few tens of femtoseconds. We explore the dependence of this coherent delocalization on coupling strength and on the magnitude of energetic noise. At longer times we observe continued migration toward a uniform population distribution that proceeds through an incoherent, diffusive mechanism. A series of simulations modeling exciton harvesting in domains of varying size demonstrates that smaller domains enhance ultrafast exciton harvesting yield. Our nonatomistic model falls short of quantitative accuracy but demonstrates that excitons are mobile within electron donor domains on ultrafast time scales and that coherent exciton transport can enhance ultrafast exciton harvesting.

Adsorption and visible-light photodegradation of organic dyes with TiO2/conjugated microporous polymer composites

“…These values are comparable to some of the newly developed photocatalysts. 27,34 Meanwhile, the photocatalytic performance of 10% TrCMP-TiO 2 shows no obvious decrease aer 3 cycle tests. The use of conjugated microporous polymers and their composite materials as both adsorbents and photocatalysts for the removal of organic dyes in water provides a valuable insight towards wastewater treatment.…”

“…21,22 Although CMPs have been extensively studied as photocatalysts for organic reactions or hydrogen evolution by water splitting, 23,24 there are few reports of CMPs as photocatalysts for degradation of organic pollutants. 25,26 Meanwhile, it has been well evidenced in organic photovoltaics that fabrication of heterojunction structure with organic-inorganic semiconductor composites is an efficient way to improve photogenerated charge separation, 27,28 which would also be highly benecial for photodegradation. 29 Herein, we prepared a triazine-containing CMP (TrCMP) via Suzuki coupling reaction.…”