Effect of P3HT/TiO2 interface modification on the photovoltaic behavior of hybrid solar cells
Date Issued
2008
Date
2008
Author(s)
Shen, Tsung-Lung
Abstract
In this article, we fabricated the ordered BHJ solar cells based on P3HT and ordered mesoporous TiO2 film which affords more hrterojunction area for charge separation and direct path for charge transport. irstly, mesoporous TiO2 films were prepared by dip-coating a EtOH solution of titania precursor and structure-directing triblock copolymer, (EO)20(PO)70(EO)20, on a densed TiO2-covered/SnO2:F (FTO) glass substrate, followed by sintering at 450℃. Experimental results of FE-SEM and XRD indicated the thus prepared TiO2 had order mesoporous structure with a pore diameter of around 10 nm and was in all anatase phase. Subsequently, the ordered BHJ solar cells was prepared by spin-coating P3HT on top of the mesoporous TiO2 film and then at different temperature for various periods. Experimental results of UV-Vis data showed a visible blue-shift after heat treatment, reveling the intriltration of P3HT into the mesooprpus TiO2 resulted in the formation of a more coil-like structure.n order to improve the compatibility of P3HT and TiO2, a OH-bearing polythiophene, poly[3-(6-hydroxyl- hexanyl)thiophene-co-3-hexylthiophene) (P3HT-OH), was synthesized via the GRIM method using 2-bromo-3-hexylthiophene and 2-bromo-3-(6-(2-tetrahydropyranyloxy)hexyl)thiophene as monomers, followed by the deprotection of OH moieties with HCl. 1H-NMR and gel permeation chromatography (GPC) data revealed the copolymer contained 10 % of hydroxyl group and had a weight-average molecular weight (Mw) of about 25000. Subsequently, the device was fabricated by replacing P3HT with P3HT-OH. However, the JSC of the device is lower than that of the reference device. The UV-Vis spectrum of P3HT-OH/TiO2 film showes the P3HT-OH has shorter conjugation length and less crystallinity than P3HT, which may correspond to the increase in series resistance (RS) and then the decrease in JSC. orever, a series of low bandgap thiophene-based molecules (WL-1~WL-4) that possess a LUMO level beyween the LUMO of P3HT and the conduction band of TiO2 as surface modifier of TiO2. After modifying TiO2 film with WL-1 ~ WL-4 by self-assembled monolayers mothod (SAMs), all JSC were higher than 1 mA/cm2 ( under A.M. 1.5G, 100 mW/cm2). The cell with WL-4 as interface modifier gave the best photovoltaic properties with a VOC of 0.8 V, a JSC of 2.3 mA/cm2, and power conversion efficiency of 1.01 % (under A.M. 1.5G, 100 mA/cm2), and external quantum efficiency (EQE) was substantially increased from 2.5 % (for the reference device) to 11 %.
Subjects
organic solar cells
poly(3-hexylthiophene)
mesoporous TiO2
interface modifier
self-assembled monolayers
SDGs
Type
thesis
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