Organic Assemblies

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Lightweight and flexible, cheap, environmentally-benign, and strongly absorbing, organic assemblies are promising for next-generation energy conversion applications. However, many organic-based solar energy conversion devices suffer from low efficiency and degradation. Improvement in either area relies on understanding the fundamental properties of these materials and hybrid interfaces with other organics (e.g. donor-acceptor) and inorganics (e.g. metal contact or photoabsorbing semiconductor catalyst). But that understanding is hindered by the challenges in characterizing the electronic structure of organic materials, both experimentally and theoretically, at nanometer length scales.

 

In ongoing work, we are applying many-body perturbation theory to compute structure and low-energy optical excitations for archetypal organic semiconductors pentacene (PEN), perfluoropentacene (PFP), and their composite donor-acceptor assemblies. We are extending existing methods to incorporate Stokes lattice couplings, finite-temperature effects and disorder, with the goal of exploring their significance on the nature and energetics of the excited state. This work will provide a foundation for long-term, time-dependent studies of exciton transport, with the aim of connecting with high-resolution near-field probe techniques and ultrafast time-resolved spectroscopy.

Optimizing open-circuit voltage (Voc) remains a significant challenge for organic photovoltaics (OPV). In OPVs, where small molecules or polymers comprise donor and acceptor, Voc depends largely on atomic-level details of the donor-acceptor interface. This dependence is not well understood, however, because interfacial energetics are extremely challenging to probe experimentally.

To address this problem, we use a parameter-free density functional theory-based method to get quantitative insight into the electronic structure and morphology of OPV donor-acceptor interfaces.

As prototypical organic systems, pentacene and PTCDA are central to the growing field of molecular-scale science, yet their electronic and optical properties are not well understood. Applying the tools of many-body perturbation theory to these systems, we study charge transport and optical absorption, and probe the nature of optically generated excitons.

Related Publications

82 Sharifzadeh JPCL
S. Sharifzadeh, P. Darancet, L. Kronik, and J. B. Neaton, "Low-energy charge-transfer excitons in organic solids from first-principles: The case of pentacene," J. Phys. Chem. Lett. 4, 2197 (2013). Abstract
66 Sharifzadeh PRB 2012

S. Sharifzadeh, A. Biller, L. Kronik, and J. B. Neaton, "Quasiparticle and Optical Spectroscopy of the Organic Semiconductors Pentacene and PTCDA from First Principles," Phys. Rev. B 85, 125307 (2012). Abstract

62 Isaacs JPCL 2011

E. B. Isaacs, S. Sharifzadeh, B. Ma, and J. B. Neaton, "Relating Trends in First-Principles Electronic Structure and Open-Circuit Voltage in Organic Photovoltaics," J. Phys. Chem. Lett. 2, 2531–2537 (2011). Abstract