Photogenerated charge carrier transport in p-polymer n-polymer bilayer structures

Manoj, Aluri; Alagiriswamy, A. A.; Narayan, K. S.

doi:10.1063/1.1600829

Cited by 35 publications

(36 citation statements)

References 36 publications

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“…Such behavior can be accounted for by the well-known antibatic characteristics by the internal filter effect. [38][39][40][41][42][43] The relationship between photocurrent and absorption spectra can be classified as one of two types for organic semiconductors: symbatic and antibatic. If the maximum photocurrent is obtained for the most strongly absorbed light, the photocurrent response is said to be symbatic with the absorption spectrum.…”

Section: Resultsmentioning

confidence: 99%

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

Noh¹,

Kim²,

Yase³

2005

Journal of Applied Physics

195

135

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Organic phototransistors (OPTs) were fabricated from pentacene and copper phthalocyanine (CuPC) based on the geometry of organic field-effect transistors (OFETs); and the effect of the wavelength of the incident light source on their performance was examined. High performance OFETs with pentacene and CuPC were fabricated and the characteristics of the OPTs were examined under UV and visible-light irradiations with top illumination. The CuPC and pentacene OPTs show a high responsivities of 0.5–2 and 10–50A∕W and maximum IPh∕IDark of 3000 and 1.3×105, respectively, under 365nm UV light. However, under visible light, at a wavelength of 650nm, the pentacene OPTs had 100 times less responsivity, 0.15–0.45A∕W, and a IPh∕IDark of 1000, even though an absorption coefficient three times larger was observed at this wavelength than at 365nm. A strong correlation was found between the performance of the OPTs and the incident photon to current conversion efficiency spectra of an organic semiconductor. The strong dependence on the wavelength of incident light of the performance of the prepared OPTs can be explained by an internal filter effect in which light with a large absorption coefficient is filtered at the top surface and through the bulk of the film when light is directed onto the opposite side of the OFET gate electrode. Thus, light cannot efficiently contribute to the generation of charge carriers in the channel regions that were formed in the first two molecular layers adjacent to the dielectric interface. Consequently, the most efficient OPTs were produced when the following conditions of incident light were satisfied: The photon energies (or frequencies) should be (i) larger than the band gap and (ii) have a relatively small absorption coefficient, since the light can penetrate down to the channel layer more efficiently when it is near the dielectric interface without any loss in absorption through the film.

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Section: Resultsmentioning

confidence: 99%

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

Noh¹,

Kim²,

Yase³

2005

Journal of Applied Physics

195

135

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“…However, this bilayer structure did not result in higher efficiency and is probably limited by the presence of defects at the bilayer junctions. [32] Efforts are ongoing to control the concentration gradient of the LC polymer vertically (with maximum concentration at the anode and a greater amount of CNPPV at the cathode end) to minimize the LC/CNPPV interface. Vertically segregated blends for this kind of system can form an optimized structure for photovoltaic devices, where the relative position of the phases plays an major role in improving the transport of charge carriers.…”

Section: Gupta Et Al/graded-bandgap Polymers For Photovoltaic Cellsmentioning

confidence: 99%

An Efficient Bulk‐Heterojunction Photovoltaic Cell Based on Energy Transfer in Graded‐Bandgap Polymers

Gupta

Kabra

Kolishetti

et al. 2006

Adv Funct Materials

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It is demonstrated that the energy transfer from low‐conjugated (LC) poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene] (MEHPPV) to high‐conjugated (HC) MEHPPV, coupled with significant electron transfer from HC‐MEHPPV to an acceptor species, offers a viable route for an efficient photodiode over a wide spectral range. An enhanced incident‐photon‐to‐current conversion efficiency (IPCE) of 19 % over a wide spectral range and a power‐conversion efficiency (ηP) of 1 % (under monochromatic illumination at λ ∼ 530 nm and a power density of ca. 1 mW cm–2) are achieved in a ternary polymer‐blend film that consists of HC‐MEHPPV (low bandgap), LC‐MEHPPV (high bandgap), and an acceptor polymer, cyanoPPV (CNPPV), in an optimized ratio. The decisive role of the morphology that emerges during phase separation in the polymer blend is demonstrated by wide‐field photocurrent imaging.

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“…However, previous studies that have employed this technique have generally used it only to characterize the response time of polymer devices, with little further analysis of the observed dynamics. 12,13 An exception is the study by Rappaport et al 14 where step function measurements were used to study the timescales for transport of charges through the device. However, this study was concerned with charge transport through an unblended polymer film rather than the dynamics of bulk-heterojunction solar cells under continuous illumination.…”

Section: Introductionmentioning

confidence: 99%

Photocurrent transients in all-polymer solar cells: Trapping and detrapping effects

McNeill

Hwang

Greenham

2009

Journal of Applied Physics

154

157

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We have studied photocurrent transients in all-polymer bulk-heterojunction solar cells based on poly(3-hexylthiophene) and poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl). By illuminating devices with square pulses of light of varying intensity, we reveal nonlinear photocurrent transients on the timescale of tens of microseconds. These microsecond photocurrent transients are attributed to the effects of trapping and detrapping of charges on this timescale, in particular, electrons. The buildup of trapped electrons results in the appearance of a peak in the photocurrent at high intensities at ∼10 μs after turn on. This trapped charge produces a local reduction in the strength of the internal electric field near the anode resulting in a net decrease in charge separation efficiency and an increase in the likelihood of bimolecular recombination due to increased and overlapping electron and hole densities. After turn off, a long photocurrent tail is observed with charge still being extracted after 0.5 ms consistent with the detrapping of deeply trapped charges. We are able to reproduce the observed transient photocurrent features using a time-dependent drift-diffusion model incorporating the trapping and detrapping of electrons.

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Photogenerated charge carrier transport in p-polymer n-polymer bilayer structures

Cited by 35 publications

References 36 publications

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance

An Efficient Bulk‐Heterojunction Photovoltaic Cell Based on Energy Transfer in Graded‐Bandgap Polymers

Photocurrent transients in all-polymer solar cells: Trapping and detrapping effects

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