Solar Energy Conversion Based on Organic and Organic/Inorganic Hybrid Solar Cells
No Thumbnail Available
Date
2007-04
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa Universty
Abstract
Solar energy conversion based on organic and organic/inorganic hybrid solar cells has been
studied in different types of photoelectrochemical cells (PECs). PECs that consist of
Eu2+/Eu3+ and I3
-/I- have been designed and studied for their photoresponse behavior. In
devices that consist of Eu2+/Eu3+ in methanol, liquid-state PECs using the emeraldine base
form of polyaniline (EB) as a photoactive material have been fabricated and studied for their
photoresponse behaviors. The photoresponse of EB:Nc-TiO2-based PEC is significantly
higher than that of EB-based and Nc-TiO2-based PECs. A PEC with a structure:
Glass/ITO/EB:Nc-TiO2/Electrolyte/Pt produced an open circuit voltage (VOC) of 0.205 V
and short-circuit current (ISC) of 105 μA/cm2 under 50 mW/cm2 white light illumination.
The device showed an induced photon-to-current conversion efficiency (IPCE) of 80% and
8% at 370 nm and 700 nm, respectively. Different systems of devices that consist of I3
-/Ihave
been studied for their photoresponse behaviors. In liquid-state PECs, separate and
comparative studies were conducted where the photoactive electrodes consist of chemically
prepared poly[3-hexylthiophene], P3HT, and electrochemically prepared poly[3-(2’,5’-
dialkoxyphenyl)thiophenes]. In P3HT-based PECs, a comparative study was done between
cells consisting of photoactive electrodes of P3HT and a composite of nc-TiO2 and P3HT.
P3HT based devices showed a VOC of 160 mV, an ISC of 2.4 μA/cm2 and a fill factor (FF) of
0.42 when illuminated with white light intensity of 100 mW/cm2. Nc-TiO2/P3HT based
devices showed better performance with a VOC of 0.51 V, an ISC of 0.31 mA/cm2, and a FF
of 0.51 when illuminated under the same condition. The IPCE% obtained at 550 nm for
P3HT-based devices and for nc-TiO2/P3HT-based devices were 0.18% and 4%,
respectively. In P3HT-based devices, P3HT showed its p-type behavior while in nc-
TiO2/P3HT based devices, P3HT acted as a sensitizer to nc-TiO2. In poly[3-(2’,5’-
dialkoxyphenyl)thiophenes] based cells, poly[3-(2’,5’-dioctyloxyphenyl)thiophene], poly[3-
(2’,5’-diheptyloxyphenyl)thiophene] and poly[3-(2’,5’-dibutyloxyphenyl)thiophene] were
electrochemically deposited on nc-TiO2 coated ITO-glass. The redox properties of the
polymers were characterized using cyclic voltammetry. The energy levels of the highest
occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals
(LUMO) have been estimated from their cyclic voltammograms and UV-Vis absorption
spectra. The poly[3-(2’,5’-dialkoxyphenyl)thiophenes] sensitize nc-TiO2 in liquid-state photoelectrochemical cells. The investigated polythiophenes with longer dialkoxyphenyl
substituents exhibited a lower photoelectrochemical cell performance. The results show that
the expected better exciton and hole mobility of shorter polydialkoxyphenyl substituted
thiophenes can be used for solar cell application by improving the film properties of the
polymers. In solid-state polymer-sensitized photoelectrochemical cells, we have designed
devices where poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene], MEH-PPV,
was used as a sensitizer to TiO2 and as electron donor to C60. The ion-conducting polymer,
poly[oxymethylene-oligo(oxyethylene)] complexed with I3
-/I- redox couple was used as a
solid polymer electrolyte. It has been observed that PECs with a composite of the inorganic
semiconductors/MEH-PPV photoactive electrodes exhibit improved cell performances when
compared with MEH-PPV based PECs. Nc-TiO2/MEH-PPV based devices produced an ISC
of 0.145 mA/cm2, and a VOC of 410 mV at light intensity of 100 mW/cm2. The power
conversion efficiency, the FF and the IPCE% were 0.03% and 0.5 and 1.8%, respectively.
In PECs based on MEH-PPV/C60, an IPCE% of 0.32% and a VOC of 281 mV and an ISC of
13.4 μA cm-2 were obtained at light intensity of 100 mW/cm2. Our results show that
organic/inorganic hybrid PECs show improved performance when compared with organic
based PECs and polymer-sensitized PECs could be alternates in designing solar energy
conversion devices.
Keywords: Polymer-sensitized photoelectrochemical cell; Solar cell characteristics;
Electrochemical polymerization; Semiconducting polymer; Nano-crystalline titanium
dioxide; Buckminsterfullerene; Poly[oxymethylene-oligo(oxyethylene)]; Redox couple.
Description
Keywords
Polymer-sensitized photoelectrochemical cell; Solar cell characteristics; Electrochemical polymerization; Semiconducting polymer; Nano-crystalline titanium dioxide; Buckminsterfullerene; Poly[oxymethylene-oligo(oxyethylene)]; Redox couple.