Schumann, Stefan (2011) Interface modification in organic and hybrid photovoltaics. PhD thesis, University of Warwick.

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Abstract

With the growing importance of organic photovoltaics (OPVs) as an attractive, low
cost and sustainable energy source the field has been investigated intensively, showing
high potential for commercialisation. To further improve device performance, different
routes of development have been explored targeting interfaces that play a crucial role in
device performance including the donor (D)/acceptor (A) and electrode/photoactive layer
interfaces, as well as incorporation of new materials.
Vertical co-deposition of water-soluble small molecule copper(II) phthalocyaninetetrasulfonic
acid tetrasodium salt (TSCuPc) and polymeric sodium poly[2-(3-
thienyl)ethoxy-4-butylsulfonate] (PTEBS) with polystyrene (PS) nanospheres to
template, followed by solvent vapour sphere removal, is shown as an excellent method to
generate three-dimensionally ordered macroporous large area thin films of sub-100 nm
pore size. After a subsequent infiltration by the electron acceptor phenyl-C61-butyric acid
methyl ester (PCBM), three-dimensionally (3D) interdigitated D-A composite structures
are generated which are further implemented in complete OPV devices. PTEBS based 3D
nanostructured D-A composite devices reached a comparable performance to planar
reference devices but did not show the expected photocurrent improvement. This is most
likely due to the complexity of this multistep fabrication method and the large probability
if impurities in the films. However, it demonstrates a new approach towards
nanoengineered 3D interdigitated organic D-A composite OPV devices.
For this templating technique monodisperse sub-100 nm PS nanospheres were
synthesised by radical initiated surfactant-free emulsion polymerisation controlling
different parameters with particular focus on styrene-4-sulfonic acid sodium salt (NaSS)
co-monomer concentration. Furthermore, planar heterojunction OPV devices from
TSCuPc and PTEBS were studied in detail and optimised for further understanding of the
3D D-A composite devices.
A substantial increase in device performance and operational stability in solution
processed inverted bulk heterojunction (BHJ) OPVs is demonstrated by introducing a
zinc oxide (ZnO) or titanium oxide (TiOx) interlayer between the electron collecting
bottom electrode and the photoactive blend of poly(3-hexylthiophene) (P3HT) and
PCBM. The introduction of transition metal oxide (TMO) interlayers resulted in a
remarkable increase in power conversion efficiency (PCE) with a maximum value of
4.91 %. The structure and morphology of the dense, planar ZnO layers was controlled
either by electrodeposition or spray pyrolysis techniques.
Organic/inorganic hybrid OPVs combine the advantages of both types of
semiconductors and offer an alternative to replace fullerene based electron acceptor
materials. The small molecule organic semiconductor, boron subphthalocyanine chloride
(SubPc), is a promising donor material for fabrication of inverted planar hybrid solar
devices using TiOx as the electron acceptor. The TiOx/SubPc cells demonstrate
performance characteristics comparable to the best-reported polymer/TiOx hybrid cells. A
relatively high photocurrent and a maximum external quantum efficiency (EQE) of 20 %
lead to a PCE of 0.4 % under AM1.5 solar illumination.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QD Chemistry T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Photovoltaic cells -- Design and construction, Organic electronics
Official Date:	March 2011
Dates:	Date Event March 2011 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Jones, Tim S.
Sponsors:	BP Solar (Firm)
Extent:	xv, 201 leaves : ill., charts
Language:	eng

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