Open‐Circuit Voltage and Effective Gap of Organic Solar Cells

Widmer, Johannes; Tietze, M Max; Leo, Karl; Riede, Moritz

doi:10.1002/adfm.201301048

Cited by 85 publications

(115 citation statements)

References 63 publications

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“…4.9b also displays photovoltaic gaps Γ as the sum of the mean donor IE and acceptor EA: Since the chemical potentials for holes and electrons, µ e and µ h , lie fairly deep in the respective DOS, the difference Γ − V oc amounts to around 0.6 eV for the mildly disordered systems (P3HT, sexithiophene, pentacene), but grows considerably with energetic disorder, reaching 0.9 eV for D5M/C 60 . This finding is supported by a number of studies [152,157,158] where energetic disorder has been hypothesized as a contribution to the observed gap: Experimentally, Γ − V oc has been located at around 0.5 eV [152], but a universality to this relationship has been disproved [158]. This apparent universality is due to the influence of thermal motion on always the same energy scale, k B T .…”

Section: The Charge-density-dependent Open-circuit Voltagesupporting

confidence: 63%

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

Poelking

2018

Springer Theses

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The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors The rational design of organic semiconductors for optoelectronic devices relies on a detailed understanding of how their molecular and morphological structure condition the energetics and dynamics of charged and excitonic states. Investigating the role of molecular architecture, conformation, orientation and packing, this work reveals mechanisms that shape the spatially resolved densities of states in organic, small-molecular and polymeric heterostructures and mesophases. The underlying computational framework combines multiscale simulations of the material morphology at atomistic and coarse-grained resolution with a long-range-polarized embedding technique to resolve the electronic structure of the molecular solid. We show that longrange electrostatic interactions tie the energetics of microscopic states to the mesoscopic structure, with a qualitative and quantitative impact on charge-carrier level profiles across organic interfaces. The computational approach provides quantitative access to the charge-density-dependent opencircuit voltage of planar heterojunctions. The derived and experimentally verified relationships between molecular orientation, architecture, level profiles and open-circuit voltage rationalize the acceptor-donor-acceptor pattern for donor materials in high-performing solar cells. Proposing a pathway for barrier-less dissociation of charge transfer states, we highlight how mesoscale fields generate charge splitting and detrapping forces in systems with finite interface roughness. The associated design rules reflect the dominant role played by lowest-energy configurations at the interface. Acknowledgements 121 Die (nicht-)lokale Zustandsdichte elektronischer Anregungen in organischen Halbleitern List of Publications 123Bibliography 125 Chapter 1 Organic Electronics in a NutshellThe discovery of conductive polymers in the 1970s [1,2] -rewarded with the Nobel prize in chemistry in the year 2000 -and subsequent development of the first polymeric electronic devices in the 1980s [3-5] have marked the beginnings of a vast interdisciplinary research field referred to as organic electronics. Drawing from both polymeric and small-molecular semiconductors, organic thin-film transistors, solar cells, light-emitting diodes, photodetectors and sensors name just a few out of many applications that make use of the supreme chemical versatility and mechanical flexibility of the underlying "soft" molecular materials. Furthermore enabling low-temperature solution-based processing, printing and spray coating, organic electronics is set to complement the conventional silicon-based electronics in diverse waysadding functionality and improving sustainability. This introductory chapter will provide a short review of the materials and device physics, as well as of new trends and challenges that emerged in the field over the past decade. MaterialsOrganic semiconductors are molecular materials that exist at the interface between orga...

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Section: The Charge-density-dependent Open-circuit Voltagesupporting

confidence: 63%

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

Poelking

2018

Springer Theses

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“…For ZnPc/C 60 and F 4 ZnPc/C 60 , the loss term ᭝ is similar with approximately 0.4 eV and is remarkably small in comparison to other OPVCs. [ 5,7,8 ] In contrast, for F 8 ZnPc/C 60 -based devices a loss of 0.79 eV is detected. Due to an insuffi cient energetic offset at the D/A interface (see Figure 5 b), exciton dissociation is presumably limited in these devices.…”

Section: Investigation Of the J ( V ) Characteristicsmentioning

confidence: 84%

“…[ 1,2 ] which is attributed to radiative and nonradiative recombination processes, was estimated to be 0.4-0.6 eV at room temperature under AM 1.5 standard illumination conditions. [5][6][7][8] …”

Section: Introductionmentioning

confidence: 99%

The Effect of Gradual Fluorination on the Properties of F_nZnPc Thin Films and F_nZnPc/C₆₀ Bilayer Photovoltaic Cells

Brendel

Krause

Steindamm

et al. 2015

Adv Funct Materials

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Motivated by the possibility of modifying energy levels of a molecule without substantially changing its band gap, the impact of gradual fl uorination on the optical and structural properties of zinc phthalocyanine (F n ZnPc) thin fi lms and the electronic characteristics of F n ZnPc/C 60 ( n = 0, 4, 8, 16) bilayer cells is investigated. UV-vis measurements reveal similar Q-and B-band absorption of F n ZnPc thin fi lms with n = 0, 4, 8, whereas for F 16 ZnPc a different absorption pattern is detected. A correlation between structure and electronic transport is deduced. For F 4 ZnPc/C 60 cells, the enhanced long range order supports fi ll factors of 55% and an increase of the short circuit current density by 18%, compared to ZnPc/C 60 . As a parameter being sensitive to the organic/organic interface energetics, the open circuit voltage is analyzed. An enhancement of this quantity by 27% and 50% is detected for F 4 ZnPc-and F 8 ZnPc-based devices, respectively, and is attributed to an increase of the quasi-Fermi level splitting at the donor/acceptor interface. In contrast, for F 16 ZnPc/C 60 a decrease of the open circuit voltage is observed. Complementary photoelectron spectroscopy, external quantum effi ciency, and photoluminescence measurements reveal a different working principle, which is ascribed to the particular energy level alignment at the interface of the photoactive materials.

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“…43 Indeed, the difference between the donor HOMO and the acceptor LUMO determines V oc as a first approximation. 44 In addition, gap defect states are known to modulate the Fermi level position that ultimately establishes the output V oc . 35 Increased defect density in the aged device should in theory decrease the V oc as these defects should reduce Fermi level shift upon illumination.…”

Section: Discussionmentioning

confidence: 99%

Nanoscale mapping by electron energy-loss spectroscopy reveals evolution of organic solar cell contact selectivity

Guerrero

Pfannmöller

Коваленко

et al. 2015

Organic Electronics

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Organic photovoltaic (OPV) devices are on the verge of commercialization being long-term stability a key challenge. Morphology evolution during lifetime has been suggested to be one of the main pathways accounting for performance degradation.There is however a lack of certainty on how specifically the morphology evolution relates to individual electrical parameters on operating devices. In this work a case study is created based on a thermodynamically unstable organic active layer which is monitored over a period of one year under non-accelerated degradation conditions. The morphology evolution is revealed by compositional analysis of ultrathin cross-sections using nanoscale imaging in scanning transmission electron microscopy (STEM) coupled with electron energy-loss spectroscopy (EELS). Additionally, devices are electrically monitored in real-time using the non-destructive electrical techniques as capacitancevoltage (C-V) and Impedance Spectroscopy (IS). By comparison of imaging and electrical techniques the relationship between nanoscale morphology and individual electrical parameters of device operation can be conclusively discerned. Is it ultimately observed how the change in the cathode contact properties occurring after the migration of fullerene molecules explains the improvement in the overall device performance.

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Open‐Circuit Voltage and Effective Gap of Organic Solar Cells

Cited by 85 publications

References 63 publications

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

The Effect of Gradual Fluorination on the Properties of F_nZnPc Thin Films and F_nZnPc/C₆₀ Bilayer Photovoltaic Cells

Nanoscale mapping by electron energy-loss spectroscopy reveals evolution of organic solar cell contact selectivity

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Open‐Circuit Voltage and Effective Gap of Organic Solar Cells

Cited by 85 publications

References 63 publications

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

The Effect of Gradual Fluorination on the Properties of FnZnPc Thin Films and FnZnPc/C60 Bilayer Photovoltaic Cells

Nanoscale mapping by electron energy-loss spectroscopy reveals evolution of organic solar cell contact selectivity

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The Effect of Gradual Fluorination on the Properties of F_nZnPc Thin Films and F_nZnPc/C₆₀ Bilayer Photovoltaic Cells