The Effect of Thermal Treatment on the Morphology and Charge Carrier Dynamics in a Polythiophene-Fullerene Bulk Heterojunction

Savenije, TJ; Kroeze, JE Jessica; Yang, Xiaoniu; Loos, Joachim

doi:10.1002/adfm.200400559

Cited by 250 publications

(267 citation statements)

References 31 publications

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“…The morphology of solar cells within the bulk heterojunction layer has been shown to be strongly affected by thermal annealing treatments [26][27][28]. The UV-visible spectra of P3HT:PCBM (1:0.6) deposited on KBr substrate are shown in Figure 2a.…”

Section: Evolution Of the P3ht:pcbm Blended Films Deposited On Inert mentioning

confidence: 99%

Morphology and photochemical stability of P3HT:PCBM active layers of organic solar cells

Dupuis

Tournebize

Bussière

et al. 2011

Eur. Phys. J. Appl. Phys.

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We report on the effects of continuous UV-visible light illumination at 60°C in the absence of oxygen on P3HT:PCBM blend films commonly used active layer of bulk heterojunction solar cells. A full description of the behavior of P3HT:PCBM blend films either unconfined or confined by an Al cathode and a PEDOT:PSS layer during annealing treatment and irradiation is provided. We also focused on the impact of the P3HT-type on the photostability. It was shown that the microstructure of P3HT dramatically influenced the photodegradation process of P3HT thin films deposited on inert substrate. The rate of photodegradation process was decreased when P3HT was blended with PCBM. It was shown that the photostability of the 2 active layer was not influenced by a PEDOT-PSS sub-layer. Solar cells were then fabricated from high-regioregular P3HT. Many large PCBM crystals were observed in P3HT:PCBM blend films and it was shown that the top surface of the active layer in contact with the Al cathode was nearly entirely composed of P3HT. Both results account for the low performances of the devices. Finally, photo-ageing experiments provoked a rapid failure of the Al cathodes which was tentatively attributed to an increase of internal strain within the devices.

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Section: Evolution Of the P3ht:pcbm Blended Films Deposited On Inert mentioning

confidence: 99%

Morphology and photochemical stability of P3HT:PCBM active layers of organic solar cells

Dupuis

Tournebize

Bussière

et al. 2011

Eur. Phys. J. Appl. Phys.

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“…Figure 5 displays the transient absorption (-∆T/T) data obtained for the four P3HT-containing samples. P3HT-PCBM blends are known for their significant photon-to-charge conversion ratios, 35 and the expected well-known trend for the P3HT-PCBM (60:40) control sample is observed with a long-lived absorption arising from charge separated polaron pairs. 36,37 The transient response from the P3HT bulk sample is also consistent with previously reported observations showing an initial decreased absorption that has been attributed to stimulated emission from excitons originating from some regions of regiorandom P3HT.…”

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confidence: 99%

Ultrafast Charge Separation at a Polymer−Single-Walled Carbon Nanotube Molecular Junction

et al. 2010

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We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single molecular layer around a SWNT leads to an ultrafast (∼430 fs) charge transfer between the materials. The addition of excess P3HT leads to long-term charge separation in which free polarons remain separated at room temperature. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diameter tubes are individually embedded in the P3HT matrix.KEYWORDS Carbon nanotube, P3HT, charge separation, molecular junction O rganic photovoltaic (OPV) cells have been demonstrated as low-cost alternatives to silicon-based cells, offering the possibility of low temperature "reel-to-reel" fabrication, necessary for viable large-scale power generation.1 The majority of OPV devices utilize exciton dissociation at the interface between two materials which exhibit a type-II heterojunction alignment, 2 resulting in interfacial charge separation and free polarons in the materials. However, it has been shown that for many OPV materials such as polymer-polymer blends, exciton dissociation leads to the formation of an interfacial bound geminate charge pair, termed an exciplex. [3][4][5][6][7] This species can be strongly bound and long-lived, significantly lowering charge separation efficiencies. studies demonstrating that a type-II heterojunction only exists for certain interfaces, such as between small diameter semiconducting SWNTs and regioregular poly(3-hexylthiophene) (P3HT). Even for such blends, energy transfer from the polymer to the SWNTs may compete effectively against charge transfer.In this letter, we show that charge transfer across the interface between individually dispersed SWNTs wrapped in a monolayer sheath of P3HT occurs on an ultrafast (430 fs) time scale. Generated charge pairs relax into a bound interfacial charge-transfer state or via nonradiative recombination of excitons within the nanotubes and no long-lived free polarons are observed. However, in the presence of an excess P3HT network, charge separation at room temperature is long-lived and comparable to that in a conventional P3HT-fullerene blend. This is the first time such blends have been studied using femtosecond time resolution, and we observe a charge transfer time three-magnitudes faster than reported previously. 17,18 In addition, significant long-term charge separation is observed for the first time in SWNTpolymer blends. We conclude that charge separation is only possible if small-diameter semiconducting tubes are individually embedded in an excess P3HT matrix. Our findings explain the poor polymer-SWNT device behavior to date and provide a promising route to incorporation of SWNTpolymer blen...

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“…1,2 Thermal or solvent annealing is typically used to alter the morphology of the device active layer on the nanoscale. [3][4][5][6] However, the blend film structure is a complex interplay of crystalline and amorphous mixed and demixed regions. 7,8 Understanding the formation of the optimal film morphology therefore requires knowledge of the key factors that govern mass transport in these materials.…”

mentioning

confidence: 99%

Molecular versus crystallite PCBM diffusion in P3HT:PCBM blends

Berriman¹,

Holdsworth²,

Zhou³

et al. 2015

AIP Advances

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The diffusion of PCBM in P3HT:PCBM blend films has been investigated using multi-wavelength scanning absorption microscopy (MWSAM). By studying the depletion of PCBM in the vicinity of the phase segregated PCBM-rich regions that form upon thermal annealing, we are able to measure the diffusion constant and activation energy for PCBM diffusion in P3HT:PCBM blend films. The measured kinetic parameters are consistent with the diffusion of nanoscale PCBM crystallites rather than molecular PCBM. We show that the presence of two distinct diffusion processes in these blend materials provides an explanation for the large differences that have been reported for PCBM diffusion in P3HT:PCBM blends. This insight allows us to develop a unified model for PCBM mass transport in these materials.

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The Effect of Thermal Treatment on the Morphology and Charge Carrier Dynamics in a Polythiophene-Fullerene Bulk Heterojunction

Cited by 250 publications

References 31 publications

Morphology and photochemical stability of P3HT:PCBM active layers of organic solar cells

Morphology and photochemical stability of P3HT:PCBM active layers of organic solar cells

Ultrafast Charge Separation at a Polymer−Single-Walled Carbon Nanotube Molecular Junction

Molecular versus crystallite PCBM diffusion in P3HT:PCBM blends

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