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Improved Hybrid Solar Cells via in situ UV Polymerization
Author(s) -
Tepavcevic Sanja,
Darling Seth B.,
Dimitrijevic Nada M.,
Rajh Tijana,
Sibener Steven J.
Publication year - 2009
Publication title -
small
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.785
H-Index - 236
eISSN - 1613-6829
pISSN - 1613-6810
DOI - 10.1002/smll.200900093
Subject(s) - materials science , photocurrent , polymerization , photochemistry , polymer , photoactive layer , polythiophene , monomer , chemical engineering , polymer solar cell , conductive polymer , optoelectronics , chemistry , engineering , composite material
One approach for making inexpensive inorganic–organic hybrid photovoltaic (PV) cells is to fill highly ordered TiO 2 nanotube (NT) arrays with solid organic hole conductors such as conjugated polymers. Here, a new in situ UV polymerization method for growing polythiophene (UV‐PT) inside TiO 2 NTs is presented and compared to the conventional approach of infiltrating NTs with pre‐synthesized polymer. A nanotubular TiO 2 substrate is immersed in a 2,5‐diiodothiophene (DIT) monomer precursor solution and then irradiated with UV light. The selective UV photodissociation of the CI bond produces monomer radicals with intact π ‐ring structure that further produce longer oligothiophene/PT molecules. Complete photoluminescence quenching upon UV irradiation suggests coupling between radicals created from DIT and at the TiO 2 surface via a charge transfer complex. Coupling with the TiO 2 surface improves UV‐PT crystallinity and π – π stacking; flat photocurrent values show that charge recombination during hole transport through the polymer is negligible. A non‐ideal, backside‐illuminated setup under illumination of 620‐nm light yields a photocurrent density of ≈5 µA cm 2 —surprisingly much stronger than with comparable devices fabricated with polymer synthesized ex situ. Since in this backside architecture setup we illuminate the cell through the Ag top electrode, there is a possibility for Ag plasmon‐enhanced solar energy conversion. By using this simple in situ UV polymerization method that couples the conjugated polymer to the TiO 2 surface, the absorption of sunlight can be improved and the charge carrier mobility of the photoactive layer can be enhanced.