Capacitance Spectroscopy of Light Induced Trap States in Organic Solar Cells

2016 ◽  
Vol 120 (39) ◽  
pp. 22169-22178 ◽  
Author(s):  
Robert A. Street ◽  
Yang Yang ◽  
Barry C. Thompson ◽  
Iain McCulloch
Keyword(s):  
Solar Cells ◽  
Organic Solar Cells ◽  
Trap States ◽  
Capacitance Spectroscopy

scholarly journals Charge-generating mid-gap trap states define the thermodynamic limit of organic photovoltaic devices

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Nasim Zarrabi ◽  
Oskar J. Sandberg ◽  
Stefan Zeiske ◽  
Wei Li ◽  
Drew B. Riley ◽  
...  
Keyword(s):  
Solar Cells ◽  
Organic Solar Cells ◽  
Detailed Balance ◽  
Linear Process ◽  
Open Circuit ◽  
Trap States ◽  
Organic Photovoltaic Devices ◽  
Inorganic Semiconductors ◽  
Harvesting Systems ◽  
Gap States

AbstractDetailed balance is a cornerstone of our understanding of artificial light-harvesting systems. For next generation organic solar cells, this involves intermolecular charge-transfer (CT) states whose energies set the maximum open circuit voltage VOC. We have directly observed sub-gap states significantly lower in energy than the CT states in the external quantum efficiency spectra of a significant number of organic semiconductor blends. Taking these states into account and using the principle of reciprocity between emission and absorption results in non-physical radiative limits for the VOC. We propose and provide compelling evidence for these states being non-equilibrium mid-gap traps which contribute to photocurrent by a non-linear process of optical release, upconverting them to the CT state. This motivates the implementation of a two-diode model which is often used in emissive inorganic semiconductors. The model accurately describes the dark current, VOC and the long-debated ideality factor in organic solar cells. Additionally, the charge-generating mid-gap traps have important consequences for our current understanding of both solar cells and photodiodes – in the latter case defining a detectivity limit several orders of magnitude lower than previously thought.

Trap states limited nanosecond response of organic solar cells

2010 ◽  
Author(s):  
Nico Christ ◽  
Siegfried W. Kettlitz ◽  
Simon Zufle ◽  
Sebastian Valouch ◽  
Uli Lemmer
Keyword(s):  
Solar Cells ◽  
Organic Solar Cells ◽  
Trap States

Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors

2021 ◽  
Author(s):  
◽  
Nasim Zarrabi
Keyword(s):  
Solar Cells ◽  
Charge Transfer ◽  
Charge Carrier ◽  
Organic Semiconductor ◽  
Organic Solar Cells ◽  
Impurity Content ◽  
Dielectric Constants ◽  
Embodied Energy ◽  
Model Systems ◽  
Trap States

From a technological point of view, organic semiconductor-based devices are of significant interest due to their light weight, ease of processability, conformal flexibility and potentially low cost and low embodied energy pro-duction. Motivated by these quite unique selling points, the performance of organic semiconductors has been a subject of multi-disciplinary study for more than 60 years with steady progress in applications such as solar cells, transistors, light emitting diodes and various sensors. One of the main characteristics that governs the performance of organic semiconduc-tors is their low dielectric constants, meaning they are excitonic at room temperature. A second main feature that dictates the charge carrier recom-bination and transport properties is the disordered nature of these semicon-ductors causing low charge carrier mobilities. The work described in this thesis focuses on these defining elements, and particularly their implications on photovoltaic devices. The discussion will start with a review into the main electro-optical phenomena in organic solar cells. Subsequently, a new method is presented for measuring exciton diffusion lengths based upon a low-quencher-content device structure. An anomalously large quenching volume is observed that can be assigned to long-range exciton delocaliza-tion prior to thermalization. These ultra-low-impurity content organic so-lar cells are also very useful as model systems to study and engineer trap states. Using this approach, it is found that mid-gap trap states are a universal feature in organic semiconductor donor-acceptor blends and un-expectedly contribute to charge generation and recombination. This has a profound impact on the thermodynamic limit of organic photovoltaic de-vices. Having demonstrated this important new insight it is further shown that a definitive link exists between a reduced recombination rate compared to the Langevin rate in some exceptional, high performance material sys-tems and a significant increase in the dissociation rate of charge transfer states upon post-processing of the active layer. In sum, the work presented in this thesis delivers important new insight as to the underlying dynamics of exciton generation and diffusion, charge transfer state dissociation, and indeed the ultimate fate of photogenerated free carriers.

Trap states in ZnPc:C60 small-molecule organic solar cells

2013 ◽  
Vol 87 (4) ◽  
Author(s):  
Lorenzo Burtone ◽  
Janine Fischer ◽  
Karl Leo ◽  
Moritz Riede
Keyword(s):  
Solar Cells ◽  
Small Molecule ◽  
Organic Solar Cells ◽  
Trap States

scholarly journals Sequentially Deposited versus Conventional Nonfullerene Organic Solar Cells: Interfacial Trap States, Vertical Stratification, and Exciton Dissociation

2019 ◽  
Vol 9 (47) ◽  
pp. 1902145 ◽  
Author(s):  
Jiangbin Zhang ◽  
Moritz H. Futscher ◽  
Vincent Lami ◽  
Felix U. Kosasih ◽  
Changsoon Cho ◽  
...  
Keyword(s):  
Solar Cells ◽  
Organic Solar Cells ◽  
Vertical Stratification ◽  
Trap States ◽  
Exciton Dissociation

Nanosecond response of organic solar cells and photodiodes: Role of trap states

2011 ◽  
Vol 83 (19) ◽  
Author(s):  
Nico Christ ◽  
Siegfried W. Kettlitz ◽  
Simon Züfle ◽  
Sebastian Valouch ◽  
Uli Lemmer
Keyword(s):  
Solar Cells ◽  
Organic Solar Cells ◽  
Trap States

scholarly journals Direct observation of trap-assisted recombination in organic photovoltaic devices

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Stefan Zeiske ◽  
Oskar J. Sandberg ◽  
Nasim Zarrabi ◽  
Wei Li ◽  
Paul Meredith ◽  
...  
Keyword(s):  
Solar Cells ◽  
Organic Solar Cells ◽  
Deep Trap ◽  
Organic Photovoltaic ◽  
Trap States ◽  
Photovoltaic Devices ◽  
Organic Photovoltaic Devices ◽  
Loss Mechanism ◽  
Operational Conditions ◽  
Gap States

AbstractTrap-assisted recombination caused by localised sub-gap states is one of the most important first-order loss mechanism limiting the power-conversion efficiency of all solar cells. The presence and relevance of trap-assisted recombination in organic photovoltaic devices is still a matter of some considerable ambiguity and debate, hindering the field as it seeks to deliver ever higher efficiencies and ultimately a viable new solar photovoltaic technology. In this work, we show that trap-assisted recombination loss of photocurrent is universally present under operational conditions in a wide variety of organic solar cell materials including the new non-fullerene electron acceptor systems currently breaking all efficiency records. The trap-assisted recombination is found to be induced by states lying 0.35-0.6 eV below the transport edge, acting as deep trap states at light intensities equivalent to 1 sun. Apart from limiting the photocurrent, we show that the associated trap-assisted recombination via these comparatively deep traps is also responsible for ideality factors between 1 and 2, shedding further light on another open and important question as to the fundamental working principles of organic solar cells. Our results also provide insights for avoiding trap-induced losses in related indoor photovoltaic and photodetector applications.

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