Browsing by Author "Shu, Ching-Fong"

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A Bipolar Host Material Containing Triphenylamine and Diphenylphosphoryl-Substituted Fluorene Units for Highly Efficient Blue Electrophosphorescence
(2009-09-09)
Hsu, Fang-Ming
;
Chien, Chen-Han
;
Shu, Ching-Fong
;
Lai, Chin-Hung
;
Hsieh, Cheng-Chih
Highly efficient blue electrophosphorescent organic light-emitting diodes incorporating a bipolar host, 2,7-bis(diphenylphosphoryl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (POAPF), doped with a conventional blue triplet emitter, iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C(2)]picolinate (FIrpic) are fabricated. The molecular architecture of POAPF features an electron-donating (p-type) triphenylamine group and an electron-accepting (n-type) 2,7-bis(diphenylphosphoryl)fluorene segment linked through the sp(3)-hybridized C9 position of the fluorene unit. The lack of conjugation between these p- and n-type groups endows POAPF with a triplet energy gap (ET) of 2.75 eV, which is sufficiently high to confine the triplet excitons on the blue-emitting guest. In addition, the built-in bipolar functionality facilitates both electron and hole injection. As a result, a POAPF-based device doped with 7 wt% FIrpic exhibits a very low turn-on voltage (2.5 V) and high electroluminescence efficiencies (20.6% and 36.7 lm W(-1)). Even at the practical brightnesses of 100 and 1000cd m(-2), the efficiencies remain high (20.2%/33.8 lm W(-1) and 18.8%/24.3 lm W(-1), respectively), making POAPF a promising material for use in low-power-consumption devices for next-generation flat-panel displays and light sources.
A novel fluorene-triphenylamine hybrid that is a highly efficient host material for blue-, green-, and red-light-emitting electrophosphorescent devices
(2007-11-23)
Shih, Ping-I
;
Chien, Chen-Han
;
Wu, Tang-Iy
;
Shu, Ching-Fong
;
應用化學系
TFTPA (tris[4-(9-phenylfluoren-9-yl)phenyl]amine), a novel host material that contains a triphenylamine core and three 9-phenyl-9-fluorenyl peripheries, was effectively synthesized through a Friedel-Crafts-type substitution reaction. Owing to the presence of its sterically bulky 9-phenyl-9-fluorenyl groups, TFTPA exhibits a high glass transition temperature (186 degrees C) and is morphologically and electrochemically stable. In addition, as demonstrated from atomic force microscopy measurements, the aggregation of the triplet iridium dopant is significantly diminished in the TFTPA host, resulting in a highly efficient full-color phosphorescence. The performance of TFTPA-based devices is far superior to those of the corresponding mCP- or CBP-based devices, particularly in blue- and red-emitting electrophosphorescent device systems. The efficiency of the FIrpic-based blue-emitting device reached 12% (26 cd A(-1)) and 18 lm W-1 at a practical brightness of 100 cd m(-2); the Ir(piq)(2)acac-based red-emitting device exhibited an extremely low turn-on voltage (2.6 V) and a threefold enhancement in device efficiency (9.0 lm W-1) relative to those of reference devices based on the CBP host material.
A solution-processable bipolar molecular glass as a host material for white electrophosphorescent devices
(2008)
Chien, Chen-Han
;
Kung, Liang-Rern
;
Wu, Chen-Hao
;
Shu, Ching-Fong
;
Chang, Sheng-Yuan
A solution-processable bipolar material tBu-OXDTFA comprising an electron-rich triphenylamine core and electron-deficient oxadiazole/ fluorene peripheries was synthesized. This dendrimer-like molecule not only possesses a high triplet energy (2.74 eV) but also exhibits excellent film-forming properties upon solution processing. We achieved highly efficient white electrophosphorescent OLEDs (22.3 cd A(-1), 11.6%) through solution processing, wherein the single white emitting layer was readily formed after spin-coating a solution of blue- and red-phosphor co-dopants containing tBu-OXDTFA as the host matrix.
Bright-white light-emitting devices based on a single polymer exhibiting simultaneous blue, green, and red emissions
(2007-01-23)
Chuang, Chu-Ying
;
Shih, Ping-I
;
Chien, Chen-Han
;
Wu, Fang-Iy
;
Shu, Ching-Fong
We have developed efficient white-light-emitting polymers through the incorporation of low band gap green-light-emitting benzothiadiazole and red-light-emitting bisthiophenylbenzothiadiazole moieties into the backbone of a blue-light-emitting bipolar polyfluorene copolymer. Partial energy transfer from the blue-fluorescent polyfluorene backbone to the green- and red-fluorescent components resulted in individual emissions from the three emissive species. By carefully controlling the concentrations of the low-energy-emitting species in the resulting copolymers, the emission of white light, with contributions from each of the three primary colors, was achieved. Efficient polymer light-emitting devices prepared using these copolymers exhibited luminance efficiencies as high as 4.87 cd/A with color coordinates (0.37, 0.36) that were very close to the ideal CIE chromaticity coordinates for pure white light (0.33, 0.33). In addition, the color coordinates remained almost unchanged over a range of operating potentials. A mechanistic study suggested that energy transfer from the fluorene segments to the low band gap units, rather than charge trapping, was the main operating process involved in the electroluminescent process.
Color tuning associated with heteroleptic cyclometalated Ir(III) complexes: influence of the ancillary ligand
(2007)
Chang, Chau-Jiun
;
Yang, Cheng-Han
;
Chen, Kellen
;
Chi, Yun
;
Shu, Ching-Fong
We report the preparation of a series of new heteroleptic Ir(III) metal complexes chelated by two cyclometalated 1-(2,4-difluorophenyl) pyrazole ligands (dfpz)H and a third ancillary bidentate ligand ( L. X). Such an intricate design lies in a core concept that the cyclometalated dfpz ligands always warrant a greater pi pi* gap in these series of iridium complexes. Accordingly, the lowest one-electron excitation would accommodate the pi* orbital of the ancillary L(boolean AND)X ligands, the functionalization of which is then exploited to fine-tune the phosphorescent emission wavelengths. Amongst the L. X ligands designed, three classes (series 1-3) can be categorized, and remarkable bathochromic shifts of phosphorescence were observed by (i) replacing the 2-benzoxazol-2-yl-substituent (1a) with the 2-benzothiazol-2-yl group (1b) in the phenolate complexes, (ii) converting the pyridyl group (2a) to the pyrazolyl group (2b) and even to the isoquinolyl group (2c) in the pyrazolate complexes and (iii) extending the pi-conjugation of the benzimidazolate ligand from 3a to 3b. Single-crystal X-ray diffraction study on complex [(dfpz)Ir(bzpz)] (2b) was conducted to confirm their general molecular architectures. Complex 2b was also used as a representative example for fabrication of multilayered, green-emitting phosphorescent OLEDs using the direct thermal evaporation technique.
Efficient non-doped blue-light-emitting diodes incorporating an anthracene derivative end-capped with fluorene groups
(2009)
Wu, Chen-Hao
;
Chien, Chen-Han
;
Hsu, Fang-Ming
;
Shih, Ping-I
;
Shu, Ching-Fong
We have synthesized and characterized a novel blue-emitting material, 2-tert-butyl-9,10-bis[40-(9-ptolylfluoren- 9-yl) biphenyl-4-yl] anthracene (BFAn), containing an anthracene core end-capped with 9-phenyl-9-fluorenyl groups. The presence of the sterically congested fluorene groups imparts BFAn with a high thermal decomposition temperature (T(d) = 510 degrees C) and results in its forming a stable glass (T(g) = 227 degrees C). Atomic force microscopy measurements revealed that BFAn forms high-quality amorphous films and possesses good morphological stability after annealing. Organic light-emitting diodes (OLEDs) featuring BFAn as the emitter exhibited an excellent external quantum efficiency of 5.1% (5.6 cd A(-1)) with Commission Internationale de L'Eclairage coordinates of (0.15, 0.12) that are very close to the National Television Standards Committee's blue standard. The power efficiency of our BFAn-based devices reached as high as 5.7 lmW(-1), making them superior to other reported non-doped deep-blue OLEDs.
Efficient red electrophosphorescence from a fluorene-based bipolar host material
(2009-08-01)
Chien, Chen-Han
;
Hsu, Fang-Ming
;
Shu, Ching-Fong
;
Chi, Yun
;
應用化學系
We have prepared efficient red organic light-emitting diodes (OLEDs) incorporating 2,7-bis(diphenylphosphoryl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (POAPF) as the host material doped with the osmium phosphor Os(fptz)(2)(PPh(2)Me)(2) (fPtZ = 3-trifluoromethyl-5-pyridyl-1,2,4-triazole). POAPF, which possesses bipolar functionalities, can facilitate both hole- and electron-injection from the charge transport layers to provide a balanced charge flux within the emission layer. The peak electroluminescence performance of the device reached as high as 19.9% and 34.5 lm/W - the highest values reported to date for a red phosphorescent OLED. In addition, we fabricated a POAPF-based white light OLED - containing red-[doped with OS(fPtZ)(2)(PPh(2)Me)(2)] and blue-emitting [doped with iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C(2')] picolinate, Firpic} layers - that also exhibited satisfactory efficiencies (18.4% and 43.9 lm/W). (C) 2009 Elsevier B.V. All rights reserved.
Efficient red-emitting electrophosphorescent polymers
(2008-02-26)
Yang, Xiao-Hui
;
Wu, Fang-Iy
;
Neher, Dieter
;
Chien, Chen-Han
;
Shu, Ching-Fong
We report the synthesis and characterization of a series of electrophosphorescent polymers with a polyfluorene backbone, containing a red-emitting iridium complex and carrier-transporting units as the substitutes of the C-9 position of fluorene. Different specimens and contents of the hole-transporting moieties were found to influence the electroluminescent properties of the polymers. Incorporation of a hole-transporting/electron-blocking interfacial layer and utilization of an efficient electron injection cathode led to the saturated red-emitting electrophosphorescent polymer devices with the peak luminance efficiency and power conversion efficiency of 9.3 cd A(-1) and 10.5 lm W-1, respectively. The efficiencies were 8 cd A(-1)/8 lm W-1 and 5.9 cd A(-1)/4.6 lm W-1, respectively, at 100 and 1000 cd m(-2).
Efficient white-electrophosphorescent devices based on a single polyfluorene copolymer
(2007-05-07)
Wu, Fang-Iy
;
Yang, Xiao-Hui
;
Neher, Dieter
;
Dodda, Rajasekhar
;
Tseng, Ya-Hsien
An efficient white-light-emitting polymer (W3) is realized by covalently attaching a green fluorophore and a red phosphor into the backbone and the side chains, respectively, of polyfluorene at a concentration of 0.04 mol %. In addition, charge-transporting pendant units are included to improve carrier injection and transport. White-electrophosphorescent devices with the structure ITO/PEDOT.PSSiW3/CsF/Al (ITO: indium tin oxide; PEDOT.PSS: poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene)) exhibit a low turn-on voltage of 2.8 V and a luminance of ca. 10(3) cd m(-2) at below 6 V. The peak luminance and power-conversion efficiencies are 8.2 cd A(-1) and 7.2 lm W-1, respectively. Furthermore, the device shows relatively stable white emission: the Commission Internationale d'Eclairage (CIE) chromaticity coordinates of the devices change only slightly from (0.35,0.38) at 10 mA cm(-2) to (0.33,0.36) at 100 mA cm(-2), with an almost constant color render index (CRI) value of 82 at all measured current densities.
Efficient white-light-emitting diodes based on poly(N-vinylcarbazole) doped with blue fluorescent and orange phosphorescent materials
(2006-06-19)
Shih, Ping-I
;
Shu, Ching-Fong
;
Tung, Yung-Liang
;
Chi, Yun
;
應用化學系
We have fabricated polymer white-light-emitting devices possessing a single emitting layer containing a hole-transporting host polymer, poly(N-vinylcarbazole), and an electron-transporting auxiliary, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, doped with a blue-light-emitting amino-substituted distyrylarylene fluorescent dye and an orange-light-emitting osmium phosphor. The doubly doped device exhibited an intense white emission having Commission Internationale de l'Eclairage coordinates of (0.33, 0.34), a high external quantum efficiency of 6.12% (13.2 cd/A), and a maximum brightness of 11 306 cd/m(2). The color coordinates remained unchanged over a range of operating voltages, even at luminance as high as 1x10(4) cd/m(2). (c) 2006 American Institute of Physics.
Electrophosphorescent polyfluorenes containing osmium complexes in the conjugated backbone
(2008-05-09)
Chien, Chen-Han
;
Liao, Song-Fu
;
Wu, Chen-Hao
;
Shu, Ching-Fong
;
Chang, Sheng-Yuan
Electrophosphorescent copolymers have been synthesized by covalent bonding of a red-emitting osmium complex Os(bpftz), which contains two 3-trifluoromethyl-5-(4-tert-butyl-2-pyridyl)triazolate (bpftz) cyclometalated ligands, into the backbone of a bipolar polyfluorene (PF) copolymer. Employing these copolymers, a highly efficient red polymer light-emitting diode has been realised that has an external quantum efficiency of 18.0%, a maximum brightness of 38000 cd m(-2), and an emission centered at 618 nm. In addition, after incorporating appropriate amounts of green-emitting benzothiadiazole (BT) and the aforementioned Os(bpftz) into the bipolar PF, an efficient white-light electroluminescent polymer is obtained that displays simultaneous blue, green, and red emissions.
Highly efficient non-doped blue-light-emitting diodes based on an anthrancene derivative end-capped with tetraphenylethylene groups
(2007-11-05)
Shih, Ping-I
;
Chuang, Chu-Ying
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Chien, Chen-Han
;
Diau, Eric Wei-Guang
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Shu, Ching-Fong
A novel blue-emitting material, 2-tert-butyl-9,10-bis[4-(1,2,2-triphenylvinyl)phenyl]anthracene (TPVAn), which contains an anthracene core and two tetraphenylethylene end-capped groups, has been synthesized and characterized. Owing to the presence of its sterically congested terminal groups, TPVAn possesses a high glass transition temperature (155 degrees C) and is morphologically stable. Organic light-emitting diodes (OLEDs) utilizing TPVAn as the emitter exhibit bright saturated-blue emissions (Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of x = 0.14 and y = 0.12) with efficiencies as high as 5.3% (5.3 cd A(-1)) - the best performance of non-doped deep blue-emitting OLEDs reported to date. In addition, TPVAn doped with an orange fluorophore served as an authentic host for the construction of a white-light-emitting device that displayed promising electroluminescent characteristics: the maximum external quantum efficiency reached 4.9% (13.1 cd A(-1)) with CIE coordinates located at (0.33, 0.39).
Highly Efficient Polymer White-Light-Emitting Diodes Based on Lithium Salts Doped Electron Transporting Layer
(2009-01-19)
Huang, Fei
;
Shih, Ping-I
;
Shu, Ching-Fong
;
Chi, Yun
;
Jen, Alex K. -Y.
A Li(2)CO(3)-doped water/alcohol-soluble neutral conjugated polymer is used as the electron-injection layer in a solution-processed polymer OWLED with very high efficiency. A maximum forward viewing luminous efficiency of 36.1 cd A(-1) and a power efficiency of 23.4 lm W(-1) were achieved, values comparable to those reported I-or the state-of-the-art vacuum deposited small-molecule OWLEDs.
Highly efficient red electrophosphorescent device incorporating a bipolar triphenylamine/bisphenylsulfonyl-substituted fluorene hybrid as the host
(2009)
Hsu, Fang-Ming
;
Chien, Chen-Han
;
Hsieh, Ya-Jou
;
Wu, Chen-Hao
;
Shu, Ching-Fong
We have fabricated highly efficient red phosphorescent organic light-emitting diodes (PHOLEDs) incorporating a bipolar host material, 2,7-bis(phenylsulfonyl)-9-[4-(N,N-diphenylamino)phenyl]-9-phenylfluorene (SAF), doped with 7 wt% tris(1-phenylisoquinolinolato-C(2),N)iridium(III) [Ir(piq)(3)]. Attaching the electron-donating (p-type) triphenylamine group onto the electron-accepting (n-type) 2,7-bis(phenylsulfonyl)fluorene segment (through the C9 position of the fluorene unit) imparts SAF with good morphological stability, high triplet energy gap (ET), bipolar transporting ability, and matching energy levels with adjacent carrier-transporting layers. Consequently, the SAF-based red-PHOLED exhibited a very low turn-on voltage (2.4 V) and high electroluminescence efficiencies of 15.8% and 22.0 lm W(-1), superior to those of the corresponding device incorporating a conventional host material, 4,4'-N,N'-dicarbazolbiphenyl (CBP; 3.2 V, 8.5%, and 8.4 lm W(-1), respectively). At a practical brightness of 1000 cd m(-2), the efficiencies of the SAF-based red-PHOLED remained high (13.1%, 14.4 lm W(-1)).
Highly efficient red organic light-emitting devices based on a fluorene-triphenylamine host doped with an Os(II) phosphor
(2008-06-09)
Wu, Chen-Hao
;
Shih, Ping-I
;
Shu, Ching-Fong
;
Chi, Yun
;
應用化學系
We report highly efficient red-light-emitting devices based on a fluorene-triphenylamine tris[4-(9-phenylfluoren-9-yl)phenyl]amine (TFTPA) host doped with an osmium phosphor. The sterically hindered fluorene peripheries provided a compatible environment for the osmium dopant and alleviated concentration quenching of the phosphor at high doping levels. Increasing the doping concentration from 7 to 21 wt % dramatically decreased the driving voltage of the TFTPA-based devices, leading to improved power efficiency. The 21 wt % Os-doped device exhibited maximum luminous and powder efficiencies of 29.9 cd/A and 25.2 lm/W, combined with high efficiencies at high brightness. At 1000 cd/m(2) the efficiencies remained 29.2 cd/A and 22.2 lm/W. (C) 2008 American Institute of Physics.
Highly efficient white-electrophosphorescent devices based on polyfluorene copolymers containing charge-transporting pendent units
(2007)
Wu, Fang-Iy
;
Shih, Ping-I
;
Tseng, Ya-Hsien
;
Shu, Ching-Fong
;
Tung, Yung-Liang
We have developed an efficient green-emitting polymer (FTO-BT5) through the incorporation of low-bandgap 2,1,3-benzothiadiazole (BT) moieties into the backbone of a blue-light-emitting polyfluorene copolymer (PF-TPA-OXD), which contains hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) pendent groups. A polymer light-emitting device based on this BT-containing copolymer exhibited very bright green emission having Commission Internationale d'E'nclairage (CIE) chromaticity coordinates (0.32, 0.61); the maximum brightness was 10232 cd m(-2) and the maximum luminance efficiency was 8.9 cd A(-1). In addition, a highly efficient three-band white-light-emitting diode was prepared using PF-TPA-OXD as a blue-light-emitting host doped with this green-light-emitting FTO-BT5 copolymer and a red-light-emitting Os phosphor Os(fppz). Without co-doping any other electron-and/or hole-transporting molecules, this white-light-emitting device reached a maximum external quantum efficiency of 4.1% (8.3 cd A(-1)) at a luminance of 402 cd m(-2) and a current density of 4.8 mA cm(-2). When the luminance increased from 26 cd m(-2) (0.36, 0.32) to 5258 cd m(-2) (0.33, 0.31), the corresponding CIE chromaticity coordinates remain almost unaltered and very close to the emission of pure white light; the value of eta(ext) remained above 3% in this high-luminance region.
Influence of molecular dipoles on the photoluminescence and electroluminescence of dipolar spirobifluorene
(2007-01-01)
Chiang, Chih-Long
;
Tseng, Shih-Min
;
Chen, Chin-Ti
;
Hsu, Chao-Ping
;
Wen, Yuh-Sheng
Here we study a series of strongly fluorescent spirobifluorene compounds, red PhSPDCV and blue PhSPDPV, together with their spiro "dimer" analogs, BisPhSPDCV and blue BisPhSPDPV. We found that the fluorescence quantum yield as well as the OLED performance of the strongly dipolar red PhSPDCV decrease significantly in the "dimeric" analog BisPhSPDCV, but not in the weakly dipolar PhSPDPV and BisPhSPDPV. On the other hand, by doping the highly dipolar PhSPDCV to an isolated environment having low polarity Alq3 as the host matrix and avoiding the emission-quenching dipole from the neighboring molecules, very high performance of saturated yellow OLEDs has been obtained as well.
Influence of molecular dipoles on the photoluminescence and electroluminescence of dipolar spirobifluorenes
(2008-01-24)
Chiang, Chih-Long
;
Tseng, Shih-Min
;
Chen, Chin-Ti
;
Hsu, Chao-Ping
;
Shu, Ching-Fong
This Full Paper investigates a series of strongly fluorescent donor-acceptor-substituted spirobifluorene compounds, red 2-diphenylamino-7-(2,2-dicyanovinyl)-9,9'-spirobifluorene (DCV), green 2-diphenylamino-9,9'-spirobifluorene7-carxoxaldehyde (CHO), and blue 2-diphenylamino-7-(2,2-diphenylvinyl)-9,9'-spirobifluorene (DPV), together with their spiro-linked "dimeric" analogs, 2DCV, 2,2'-bis(diphenylamino)-9,9'-spirobifluorene-7,7'-dicarboxaldehyde (2CHO), and 2,2'-bis(diphenylamino)-7,7'bis(2,2-diphenylvinyl)-9,9'-spirobifluorene (2DPV), respectively. The emission optical density and, hence, the intensity of photoluminescence (PL) or electroluminescence (EL) of the "dimeric" analogs is presumed to increase, which is beneficial for organic light-emitting diode (OLED) applications. The physical properties, including the dipole moments obtained from quantum chemistry calculations, emission solvatochromism, fluorescence quantum yield (Of) as well as the EL of these six spirobifluorene compounds have been examined in detail. We found that Of as well as OLED performance (EL efficiency and intensity) of the strongly dipolar DCV decrease significantly in the "dimeric" analog 2DCV, but less so in the moderately dipolar CHO and 2CHO, and only slightly in the weakly dipolar DPV and 2DPV. This is parallel to the intramolecular dipole moment, which is large for 2DCV, medium for 2CHO, and very small for 2DPV. Here, we show for the first time systematically that the luminescence intensity is closely correlated with the local electric field induced by the molecular dipole. A strong electric field may facilitate radiationless decay channels with a charge-transfer nature, leading to a high quenching rate. Consistent with this conclusion, which is derived from the red DCV/2DCV and green CHO/2CHO, our new blue fluorophore DPV with an essentially zero dipole moment has successfully achieved one of the best electrofluorescent blue OLEDs. At the same time, by doping the highly dipolar DCV into an isolated environment with the low-polarity Alq(3) as the host matrix, we obtained a very high performance of saturated yellow OLEDs as well, This is possibly due to the reduction of emission-quenching dipoles from the neighboring molecules. Our results have provided an important insight in designing luminescent materials, as follows: molecular dipole moments should be kept at a low magnitude to avoid quenching induced by a strong local electric field in the chromophore.
Lithium salt doped conjugated polymers as electron transporting materials for highly efficient blue polymer light-emitting diodes
(2008-12-15)
Huang, Fei
;
Shih, Ping-I
;
Liu, Michelle S.
;
Shu, Ching-Fong
;
Jen, Alex K. -Y.
Highly efficient blue polymer light-emitting diodes (PLEDs) are fabricated using a conjugated polymer, poly[9,9-bis(2-(2-(2-diethanol-amino-ethoxy) ethoxy) ethyl) fluorene-alt-4, 4(')-phenylether] as an electron transporting layer (ETL). It was found that the performance of these blue-emitting devices could be greatly improved if the ETL was doped with LiF or Li(2)CO(3) salts. A bis[(4,6-di-fluorophenyl)-pyridinato-N, C(2)] (picolinate) Ir(III) (FIrpic) complex based blue phosphorescent PLED exhibited a maximum luminance efficiency of 20.3 cd/A with a luminance of 1600 cd/m(2) at the current density of 7.9 mA/cm(2) and drive voltage of 8.0 V.
Lnfrared photocurrent response of charge-transfer exciton in polymer bulk heterojunction
(2008-02-25)
Yang, Chia-Ming
;
Tsai, Pei-Yu
;
Horng, Sheng-Fu
;
Lee, Kuan-Chen
;
Tzeng, Shin-Rong
We study the charge-transfer exciton absorption and photocurrent response in solution-processed bulk heterojunction based on poly(3-hexylthiophene) donor and (6,6)-phenyl-C(61)-butyric acid methyl ester acceptor in the near-infrared wavelength region. While the exciton absorption exists only for wavelength below 650 nm, direct generation of charge-transfer exciton formed between the donor and acceptor extends the absorption wavelength to 950 nm. For films with micrometer thickness, the photon-to-electron conversion efficiency is about 60% at 750 nm wavelength under reverse voltage bias and the photocurrent to dark current ratio is about 8.6 at 900 nm and remains 3.6 even at 1000 nm. Photodetector with high sensitivity covering exclusively the 650-1000 nm near infrared region can therefore be made without a low bandgap material. The charge-transfer exciton absorption coefficient and photocurrent sensitivity depend on the annealing condition which controls the donor-acceptor morphology. (c) 2008 American Institute of Physics.