On the Origin of Charge Generation in Hybrid TiOx/Conjugated Polymer Photovoltaic Devices

Journal Article · Thu Jan 19 04:00:00 EST 2012 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/jp209016z· OSTI ID:1045717

Segal-Peretz, Tamar; Leman, Olga; Nardes, Alexandre M.; Frey, Gitti L.

Hybrid films of donor/acceptor conjugated polymer/metal oxides are considered promising materials for low-cost, solution-processed solar cells. Because device performances depend on the nanoscale film morphologies, most attention and extensive efforts have been invested in improving the nanofabrication of hybrid films. Nevertheless, the reported conjugated polymer/metal oxide device efficiencies are still far poorer than those of all-organic and solid-state dye-sensitized metal oxide solar cells. To decouple the effect of insufficient morphology control from other generic photocurrent-limiting processes, we study the photocurrent generation at conjugated polymer-metal oxide interfaces in self-organized, highly ordered, and uniform hybrid nanostructures. A combination of small-angle X-ray scattering, high-resolution transmission electron microscopy (TEM), and energy-filtered TEM confirms the structure and composition of the highly ordered, high interfacial area hybrid cubic mesostructured films prepared by the coassembly of a titania precursor species, a water-soluble polythiophene derivative, and a block copolymer surfactant. Contactless time-resolved microwave photoconductivity (TRMC) measurements show a moderate 2-fold increase in the photoconductivity of the highly ordered TiO{sub x}/conjugated polymer mesostructured film compared to that of a pristine film of the same polymer, indicating inefficient exciton dissociation at the oxide/polymer interface. Furthermore, strong correlation between the TRMC results and the device performance reveals that most of the photogenerated carriers in the conjugated polymer/TiO{sub x} photovoltaic device originate from exciton dissociation in the polymer bulk, followed by electron transfer from the polymer to the metal oxide, and not at the interface. Therefore, the photovoltaic devices utilizing the highly ordered conjugated polymer/metal oxide mesostructured films are not primarily limited by insufficient morphology control but rather by the inefficient process of exciton dissociation in the polymer. This observation is in agreement with the low photocurrent densities generally observed in photovoltaic devices comprising conjugated polymer/metal oxide active layers.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1045717
• Report Number(s): NREL/JA-5900-52900
• Journal Information: Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 2 Vol. 116; ISSN 1932-7447
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COPOLYMERS
DISSOCIATION
ELECTRON TRANSFER
EXCITONS
MORPHOLOGY
NANOSTRUCTURES
ORIGIN
OXIDES
PERFORMANCE
PHOTOCONDUCTIVITY
PHOTOCURRENTS
POLYMERS
PRECURSOR
PV
SCATTERING
SOLAR CELLS
TRANSMISSION ELECTRON MICROSCOPY
hybrid films
photovoltaic
polymer
solar cells