53.3: Influence of Material Purification by Vacuum Sublimation on Organic Optoelectronic Device Performance

Petrich, Annette; Koch, M. H. J.; Pfützner, Steffen; Meerheim, Rico; Scholz, Sebastian; Drechsel, J.; Walzer, Karsten; Pfeiffer, Martin; Leo, Karl

doi:10.1889/1.2433332

Cited by 29 publications

(32 citation statements)

References 4 publications

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“…[ 54 ] The dopants NDP9 and NDN1 are purchased from Novaled AG (Germany) and used distribution of a given density of photogenerated carriers at different temperatures, as expected from single heterojunction solar cells. [ 48 ] The fi tted slope of V oc of the tandem device has a value of 2.73 mV K − 1 .…”

Section: Methodsmentioning

confidence: 99%

Efficient Organic Tandem Solar Cells based on Small Molecules

Riede

Uhrich

Widmer

et al. 2011

Adv Funct Materials

227

144

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In this paper, two vacuum processed single heterojunction organic solar cells with complementary absorption are described and the construction and optimization of tandem solar cells based on the combination of these heterojunctions demonstrated. The red‐absorbing heterojunction consists of C60 and a fluorinated zinc phthalocyanine derivative (F4‐ZnPc) that leads to a 0.1–0.15 V higher open circuit voltage Voc than the commonly used ZnPc. The second heterojunction incorporates C60 and a dicyanovinyl‐capped sexithiophene derivative (DCV6T) that mainly absorbs in the green. The combination of both heterojunctions into one tandem solar cell leads to an absorption over the whole visible range of the sun spectrum. Thickness variations of the transparent p‐doped optical spacer between both subcells in the tandem solar cell is shown to lead to a significant change in short circuit current density jsc due to optical interference effects, whereas Voc and fill factor are hardly affected. The maximum efficiency η of about 5.6% is found for a spacer thickness of 150‐165 nm. Based on the optimized 165nm thick spacer, effects of intensity and angle of illumination, and temperature on a tandem device are investigated. Variations in illumination intensity lead to a linear change in jsc over three orders of magnitude and a nearly constant η in the range of 30 to 310 mW cm−2. Despite the stacked heterojunctions, the performance of the tandem device is robust against different illumination angles: jsc and η closely follow a cosine behavior between 0° and 70°. Investigations of the temperature behavior of the tandem device show an increase in η of 0.016 percentage points per Kelvin between −20 °C and 25 °C followed by a plateau up to 50 °C. Finally, further optimization of the tandem stack results in a certified η of (6.07 ± 0.24)% on (1.9893 ± 0.0060)cm2 (Fraunhofer ISE), i.e., areas large enough to be of relevance for modules.

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Section: Methodsmentioning

confidence: 99%

Efficient Organic Tandem Solar Cells based on Small Molecules

Riede

Uhrich

Widmer

et al. 2011

Adv Funct Materials

227

144

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“…20 One reason for the large L D of C 60 is due to the nearly unity intersystem crossing yield from singlet to triplet excitons 86 as well as its triplet lifetime of 10-100 s. 87 Bathocuproine (BCP) is also shown in Figure 7, and is used as an exciton blocking layer (EBL) in the double heterostructure device architecture, as described in Subsection "Double heterostructure." It should be noted that material purity plays a crucial role in determining the efficiency of organic PV cells, 88,89 and therefore materials should be purified via the vacuum thermal gradient sublimation technique prior to device fabrication. 90 Figure 7 plots the extinction coefficient, k, for neat thin films of these common materials, and each material absorbs at λ ≤ 800 nm.…”

Section: Methodsmentioning

confidence: 99%

Solar cells utilizing small molecular weight organic semiconductors

Rand

Genoe

Heremans

et al. 2007

Progress in Photovoltaics

465

296

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In this review, we focus on the field of organic photovoltaic cells based on small molecular weight materials. In particular, we discuss the physical processes that lead to photocurrent generation in organic solar cells, as well as the various architectures employed to optimize device performance. These include the donor-acceptor heterojunction for efficient exciton dissociation, the exciton blocking layer, the mixed or bulk heterojunction, and the stacked or tandem cell. We show how the choice of materials with known energy levels and absorption spectra affect device performance, particularly the open-circuit voltage and short-circuit current density. We also discuss the typical materials and growth techniques used to fabricate devices, as well as the issue of device stability, all of which are critical for the commercialization of low-cost and high-performance organic solar cells.

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“…12 All organic materials had been purified by vacuum gradient sublimation to remove contaminations. 13 The C 70 had been purified four times.…”

Section: Improved Bulk Heterojunction Organic Solar Cells Employing Cmentioning

confidence: 99%

Improved bulk heterojunction organic solar cells employing C70 fullerenes

Pfuetzner

Meiss

Petrich

et al. 2009

Applied Physics Letters

109

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We show that the fullerene C70 is suitable to replace fullerene C60, which is commonly used as electron transporter and acceptor in small-molecule organic solar cells. It is shown that the higher absorption of C70 leads to high external quantum efficiencies of over 50% in the spectral range of 500–700 nm. By optimizing the energy level alignment to hole transport layers, the absorption, and the ratio of C70:zinc phthalocyanine (ZnPc) in a bulk heterojunction solar cell, an efficiency of η=2.87% is achieved. This is a substantial improvement over an identical solar cell employing C60 having η=2.27%. The efficiency increase is due to a higher photocurrent, while fill factor and open-circuit voltage for C70 and C60-containing organic solar cells remain comparable.

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53.3: Influence of Material Purification by Vacuum Sublimation on Organic Optoelectronic Device Performance

Cited by 29 publications

References 4 publications

Efficient Organic Tandem Solar Cells based on Small Molecules

Efficient Organic Tandem Solar Cells based on Small Molecules

Solar cells utilizing small molecular weight organic semiconductors

Improved bulk heterojunction organic solar cells employing C70 fullerenes

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