Browsing by Author "Ho, Zhong-Yo"

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Annealing effect of polymer bulk heterojunction solar cells based on polyfluorene and fullerene blend
(2009-02-01)
Huang, Jen-Hsien
;
Yang, Chuan-Yi
;
Ho, Zhong-Yo
;
Kekuda, Dhananjay
;
Wu, Meng-Chyi
Control of blend morphology at the nanoscale and high charge mobility is essential for polymer photovoltaic devices in terms of their power conversion efficiencies (PCE). In the case of bulk heterojunctions solar cells, both blend morphology and charge mobility are influenced by thermal treatment. In this manuscript, we study the effects of annealing temperature on polymer PV devices with blends of poly[9,9'-dioctyl-fluorene-co-bithiophene] (F8T2) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). The morphological changes of blended films were observed upon thermal annealing temperature near and above glass transition temperature (130 degrees C). Such microstructural transformations resulted in modified charge transport pathways and therefore greately influenced the device performance. The highest PCE of 2.14% with an open-circuit voltage (V(OC)) of 0.99 V and a short-circuit current (J(SC)) of 4.24 mA/cm(2) was achieved by device annealing at 70 degrees C for 20 min. (C) 2008 Elsevier B.V. All rights reserved.
Complementary inverter circuits based on p-SnO(2) and n-In(2)O(3) thin film transistors
(2008-06-09)
Dhananjay
;
Chu, Chih-Wei
;
Ou, Chun-Wei
;
Wu, Meng-Chyi
;
Ho, Zhong-Yo
Thin film transistors (TFTs) of indium oxide (In(2)O(3)) and tin oxide (SnO(2)) were fabricated on SiO(2) gate dielectric using reactive evaporation process. Structural investigation of the films revealed that In(2)O(3) films were polycrystalline in nature with preferred (222) orientation and SnO(2) films exhibited amorphous nature. The x-ray photoelectric spectroscopy measurements suggest that SnO(2) films were oxygen rich and presume mixed oxidation states of Sn, namely Sn(2+) and Sn(4+). While the In(2)O(3) based TFTs possess n-type channel conduction, SnO(2) based TFTs exhibited anomalous p-type conductivity. Integration of these n- and p-type devices resulted in complementary inverter with a gain of 11. (C) 2008 American Institute of Physics.
Complementary inverter circuits based on p-SnO2 and n-In2O3 thin film transistors
(2008-06-09)
Dhananjay
;
Chu, Chih-Wei
;
Ou, Chun-Wei
;
Wu, Meng-Chyi
;
Ho, Zhong-Yo
Thin film transistors (TFTs) of indium oxide (In2O3) and tin oxide (SnO2) were fabricated on SiO2 gate dielectric using reactive evaporation process. Structural investigation of the films revealed that In2O3 films were polycrystalline in nature with preferred (222) orientation and SnO2 films exhibited amorphous nature. The x-ray photoelectric spectroscopy measurements suggest that SnO2 films were oxygen rich and presume mixed oxidation states of Sn, namely Sn2+ and Sn4+. While the In2O3 based TFTs possess n-type channel conduction, SnO2 based TFTs exhibited anomalous p-type conductivity. Integration of these n- and p-type devices resulted in complementary inverter with a gain of 11. (C) 2008 American Institute of Physics.
Controlled Growth of Nanofiber Network Hole Collection Layers with Pore Structure for Polymer-Fullerene Solar Cells
(2008-12-04)
Huang, Jen-Hsien
;
Ho, Zhong-Yo
;
Kekuda, Dhananjay
;
Chu, Chih-Wei
;
Ho, Kuo-Chuan
In this study, we compare a series of hole collector layers (HCLs) with pore structure fabricated via an electrochemical method to construct polymer-fullerene solar cells. The HCLs with a pore structure can offer a large interface to enhance hole collection; however, the series resistances are also increased by the relatively pore morphology. Photovoltaic device with the largest short circuit current (J(sc)) and efficiency is achieved using poly(3,4-propylenedioxythiophene) (PProDoT) as HCLs due to its highly porous structure and reasonable series resistance. By further optimizing the thickness of the HCLs in the solar cell, a power efficiency of 3.57% under simulated sun light is achieved.
Effects of nanomorphological changes on the performance of solar cells with blends of poly[9,9 '-dioctyl-fluorene-co-bithiophene] and a soluble fullerene
(2009-01-14)
Huang, Jen-Hsien
;
Ho, Zhong-Yo
;
Kekuda, Dhananjay
;
Chang, Yung
;
Chu, Chih-Wei
Controlled nanophase segregation within the blended films of a conjugated polymer and a soluble fullerene has enabled us to form a continuous transfer pathway for the carriers, thereby increasing the photocurrent generation for polymer photovoltaic devices. Here, we study the effects of nanomorphological changes on the performance of polymer solar cells using blended films of poly[9,9'-dioctyl-fluorene-co-bithiophene] (F8T2) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Different weight ratios of the F8T2 and PCBM blends in various solvents were studied at different annealing temperatures. The morphology of the films seems to be a strong function of the processing conditions. The power conversion efficiency (PCE) of the photovoltaic devices has improved significantly from 0.34% to 2.14% under air mass 1.5 simulated solar illumination (100 mW cm(-2)), which could be attributed to the nanomorphological changes in the films.
Enhanced spectral response in polymer bulk heterojunction solar cells by using active materials with complementary spectra
(2010-01-01)
Huang, Jen-Hsien
;
Lee, Chuan-Pei
;
Ho, Zhong-Yo
;
Kekuda, Dhananjay
;
Chu, Chih-Wei
We have fabricated organic photovoltaic devices with blends of poly[9,9'-dioctyl-fluorene-co-bithiophene] (F8T2) and fullerene as an electron donor and electron acceptor, respectively. A significant improvement of the photovoltaic efficiency was found in device by using active materials with complementary spectra. The different weight ratios of composite film were also performed to correlate between morphology and the device performance. A power conversion efficiency (PCE) up to 2.0% with an open-circuit voltage of 0.85 V and a short-circuit current (J(SC)) of 5.3 mA/cm(2), was achieved by blending the F8T2 with [6,6]-phenyl-C71-butyric acid methyl ester (PC[70]BM). (C) 2009 Elsevier B.V. All rights reserved.
Fabrication of multilayer organic solar cells through a stamping technique
(2009)
Huang, Jen-Hsien
;
Ho, Zhong-Yo
;
Kuo, Tsung-Hsien
;
Kekuda, Dhananjay
;
Chu, Chih-Wei
In this article, we demonstrate a simple and reliable stamping technique for fabricating multi-layer solar cells. A poly(di-methylsilane) (PDMS) stamp is used for transferring the active layers onto the substrate. An intermediate solvent treatment is introduced to temporarily modify the PDMS surface; therefore, the polymer film can be uniformly formed on top of the PDMS surface. This method is involves non-contaminative and non-invasive processes, therefore it can avoid possible degradation or contamination of the polymer film and the PDMS stamp can be reused. Devices realized through this stamping technique both by direct and inverted structures exhibited power conversion efficiencies of 3.2 and 2.83% respectively.