Influence of thermal ageing on the stability of polymer bulk heterojunction solar cells

Bertho, Sabine; Haeldermans, I.; Swinnen, Ann; Moons, Wouter; Martens, Tom; Lutsen, Laurence; Vanderzande, Dirk; Manca, Jean; Senes, Alessia; Bonfiglio, Annalisa

doi:10.1016/j.solmat.2006.10.008

Cited by 160 publications

(113 citation statements)

References 20 publications

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“…[45][46][47][48] However, applying this technique to polymer blends turned out less successful, again due to lack of contrast between the polymer phases. 49 An exception was presented by Blache et al, who applied environmental scanning EM (E-SEM) to PFB:F8BT blends and obtained well-resolved images.…”

Section: Toolbox To Probe the Morphologymentioning

confidence: 99%

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Nanoscale structure of solar cells based on pure conjugated polymer blends

Veenstra

Loos

Kroon

2007

Progress in Photovoltaics

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This paper gives an overview of the status of photovoltaic devices based on blends of semiconducting polymers. The polymer blends form the bulk heterojunction in these photovoltaic devices. The fundamental mechanisms governing the performance of these devices are discussed as well as the specificities of these all-polymer solar cells. The morphology of the polymer blend layer is expected to influence the device performance of these bulk heterojunctions. An overview is presented of factors that influence the morphology of the active layer of polymer blend photovoltaic devices together with a summary of tools available to study the structure of this layer. An advanced electron microscopy technique is applied to study the morphology of polymer blends of MDMO-PPV and PCNEPV with differing molecular weights. It is shown that the molecular weight of the polymer influences the typical domain size from $200 nm down to less than 5 nm in these bulk heterojunction PV devices. No strong relation is observed between the typical length scale of the phase separated domains and the measured external quantum efficiency, indicating that the phases are intermixed.

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Section: Toolbox To Probe the Morphologymentioning

confidence: 99%

“…[45][46][47][48]54 These studies have been important for developing and understanding the device physics of polymer:fullerene PV devices. Similar studies on polymer blend PV devices are unfortunately still scarce.…”

Section: Factors Influencing the Morphology Of The Photoactive Layer mentioning

confidence: 99%

Nanoscale structure of solar cells based on pure conjugated polymer blends

Veenstra

Loos

Kroon

2007

Progress in Photovoltaics

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“…The behavior of BHJ OPVs with thermal degradation is generally correlated to morphological changes occurring in the active layer that can affect: i) charge separation process by formation of fullerene aggregates in polymer:fullerene blends, which leads to a PCE loss due to the reduction of the donor:acceptor (D:A) interfacial area [30][31][32], ii) charge extraction by a migration of a skinlayer of either polymer [33] or fullerene [34] adhering to the top contact, generating barriers or selective transport regions as a function of the device architecture; iii) transport properties by modification of the polymer packing in the blend [35,36], iv) recombination by an increase of the number of defect states at the bulk of the active layer [37], v) optical properties by generation of a charge transfer complex between donor and acceptor molecules which also acts as an exciton quencher [38]. Several works [31,32] demonstrated that morphological reorganization processes occur only if the solar cell is subjected to temperatures near or above the glass transition temperature (Tg) of the donor polymer. At this temperature devitrification of the blend allows the polymer and the fullerene molecules to rearrange/diffuse in the bulk and at the interface with the electrodes.…”

Section: Introductionmentioning

confidence: 99%

Predicting thermal stability of organic solar cells through an easy and fast capacitance measurement

Tessarolo

Guerrero

Gedefaw

et al. 2015

Solar Energy Materials and Solar Cells

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Degradation of Organic Photovoltaic (OPV) devices is currently a topic under intense research as it is one of the main limitations towards the commercialization of this technology. Morphological changes at both active layer and interfaces with the outer contacts are believed to determine main key issues to be overcome. In-line techniques are essential to rule out any effect arising during sample fabrication.Unfortunately, the number of physical techniques able to provide morphological information on complete and operational devices is certainly limited. In this work, we study the thermal degradation of bulk heterojunction (BHJ) solar cells composed by different donor polymers with techniques developed to provide in-situ information on operational devices. Capacitance measurement as a function of temperature monitors the electrical integrity of the active layer and provides the threshold temperature (T MAX ) at which the whole device becomes thermally unstable. We found a direct correlation between the threshold temperature T MAX , obtained by capacitance-temperature measurements on complete OPV devices, and the power conversion efficiency decay measured at 85°C. Devices show to be thermal stable when the temperature of the thermal stress is below the T MAX , while above the T MAX evident changes in the active layer or at the active layer/electrode interface are also detected by confocal fluorescence microscopy. The capacitance method gives precious guidelines to predict the thermal stability of BHJ solar cells using accelerated and easy tests.

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“…Hence, materials with high glass-transition temperatures have been used, resulting in a signifi cant improvement of the thermal stability of the photovoltaic parameters. [ 16 ] Transmission electron microscopy (TEM) studies have revealed that such improved thermal stability coincides with a more stable active layer morphology. The improvements are attributed to the reduced diffusion movement of the electron acceptor PCBM molecules within the active layer.…”

Section: Introductionmentioning

confidence: 99%

The Critical Role of Processing and Morphology in Determining Degradation Rates in Polymer Solar Cells

Kumar¹,

Hong²,

Sista³

et al. 2010

Advanced Energy Materials

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With rapid increase in the efficiencies of polymer solar cells (PSCs) in the last few years, the issue of device stability is taking center stage in organic photovoltaic research. In this work, the effects of oxygen and light on the degradation of charge‐transport properties of the bulk polymer active layer are studied over short timescales. It is shown that although different processing techniques produce similar efficiencies for pristine devices, they result in different degradation rates. This variation in degradation rates is primarily due to slightly different morphology parameters, such as molecular packing or disorder in the film. Investigation reveals that the choice of processing for the devices should consider degradation rates as a critical parameter, not just the efficiencies of the pristine devices. It was found that degradation starts with broadening of the effective density of states due to photo‐oxidation. Both transient absorption and charge extraction by linearly increasing voltage (CELIV) measurements show increase in disorder in the films with progressive degradation. It is suggested that annealing provides the necessary thermal energy to reduce the trap states by flattening out the energy landscape of the pristine films, improving not only the efficiency, as reported previously, but also slowing the degradation rates.

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Influence of thermal ageing on the stability of polymer bulk heterojunction solar cells

Cited by 160 publications

References 20 publications

Nanoscale structure of solar cells based on pure conjugated polymer blends

Nanoscale structure of solar cells based on pure conjugated polymer blends

Predicting thermal stability of organic solar cells through an easy and fast capacitance measurement

The Critical Role of Processing and Morphology in Determining Degradation Rates in Polymer Solar Cells

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