Monomolecular and Bimolecular Recombination of Electron–Hole Pairs at the Interface of a Bilayer Organic Solar Cell

Hahn, Tobias; Tscheuschner, Steffen; Kahle, Frank‐Julian; Reichenberger, Markus; Athanasopoulos, Stavros; Saller, Christina; Bazan, Guillermo C.; Nguyen, Thuc‐Quyen; Strohriegl, Peter; Bäßler, H.; Köhler, Anna

doi:10.1002/adfm.201604906

Cited by 64 publications

(70 citation statements)

References 56 publications

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“…The ZnO:Al 2 O 3 ‐based devices have a decreased slope with the increasing of Al 2 O 3 content, indicating a weak dependence of V OC on the I . As reported previously, a slope close to k B T/q means that the dominant recombination mechanism in ZnO:Al 2 O 3 ‐based device is bimolecular recombination. In other words, the monomolecular recombination, also termed the trap‐assisted Shockley–Read–Hall (SRH) recombination, is significantly suppressed in the ZnO:Al 2 O 3 ‐based devices.…”

Section: Photovoltaic Parameters Of Pscs Using Various Zno:al2o3 Layesupporting

confidence: 77%

Polymer Solar Cells with 90% External Quantum Efficiency Featuring an Ideal Light‐ and Charge‐Manipulation Layer

Chen

Zhu

et al. 2018

Advanced Materials

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Rapid progress in the power conversion efficiency (PCE) of polymer solar cells (PSEs) is beneficial from the factors that match the irradiated solar spectrum, maximize incident light absorption, and reduce photogenerated charge recombination. To optimize the device efficiency, a nanopatterned ZnO:Al O composite film is presented as an efficient light- and charge-manipulation layer (LCML). The Al O shells on the ZnO nanoparticles offer the passivation effect that allows optimal electron collection by suppressing charge-recombination loss. Both the increased refractive index and the patterned deterministic aperiodic nanostructure in the ZnO:Al O LCML cause broadband light harvesting. Highly efficient single-junction PSCs for different binary blends are obtained with a peak external quantum efficiency of up to 90%, showing certified PCEs of 9.69% and 13.03% for a fullerene blend of PTB7:PC BM and a nonfullerene blend, FTAZ:IDIC, respectively. Because of the substantial increase in efficiency, this method unlocks the full potential of the ZnO:Al O LCML toward future photovoltaic applications.

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Section: Photovoltaic Parameters Of Pscs Using Various Zno:al2o3 Layesupporting

confidence: 77%

Polymer Solar Cells with 90% External Quantum Efficiency Featuring an Ideal Light‐ and Charge‐Manipulation Layer

Chen

Zhu

et al. 2018

Advanced Materials

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“…[25] The intersite distance (a) is 1 nm. The index i runs from 1 to n − 1 with n being the site at distance L = 100 nm from the interface at which we consider that the electron is extracted.…”

Section: Theoretical Resultsmentioning

confidence: 99%

What is the Binding Energy of a Charge Transfer State in an Organic Solar Cell?

Athanasopoulos

Schauer

Nádaždy

et al. 2019

Advanced Energy Materials

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simple picture, be considered as an electron on the more and a hole on the less electronegative chromophore. The key step in the photogeneration of charges in organic solar cell consists in the separation of this electron-hole pair against their mutual coulomb attraction. In a medium with a dielectric constant of 3.5, the Coulomb energy of opposite point charges with mutual separation of 1 nm is 410 meV. At room temperature, the associated Boltzmann factor for dissociation, expwould thus be about 10 −7 . On other hand, in an efficient solar cell composed of appropriate electron donor and acceptor materials the internal quantum efficiency can be close to 100%, [1] and is only weakly temperature dependent. [2] For example, Gao and co-workers report activation energies for charge separation that are as low as 25 meV for P3HT:PCBM when the film is disordered, and that decrease to 9 meV when the film is better ordered after an annealing step. [2a] Similarly, Kurpiers and co-workers report 23 meV for PCPDTBT:PCBM, i.e., also in the range of thermal energy at room temperature. [2b] How can both facts, i.e., the expected high binding energy of a localized electron-hole pair and the efficient, only weaklyThe high efficiencies reported for organic solar cells and an almost negligible thermal activation measured for the photogeneration of charge carriers have called into question whether photoinduced interfacial charge transfer states are bound by a significant coulomb attraction, and how this can be reconciled with very low activation energies. Here, this question is addressed in a combined experimental and theoretical approach. The interfacial binding energy of a charge-transfer state in a blend of MeLPPP:PCBM is determined by using energy resolved electrochemical impedance spectroscopy and is found to be about 0.5 eV. Temperature-dependent photocurrent measurements on the same films, however, give an activation energy that is about one order of magnitude lower. Using analytical calculations and Monte Carlo simulation the authors illustrate how i) interfacial energetics and ii) transport topology reduce the activation energy required to separate the interfacial electron-hole pair, with about equal contributions from both effects. The activation energy, however, is not reduced by entropy, although entropy increases the overall photodissociation yield.

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“…Figure 2a shows the linear dependence of JSC on the incident light intensity, with a fit to a power law , resulting in the value of for both devices. [7] To draw the conclusion about a dominant recombination mechanism, knowledge about the upper limit of Fermi level splitting is required as this will allow us to distinguish between charge separation and charge storage dynamics. An independent illustration of dominant recombination can be drawn from VOC vs illumination intensity plot; an alternative way to obtain Fermi level splitting.…”

Section: Resultsmentioning

confidence: 99%

Influence of the Nature of A Cation on Dynamics of Charge Transfer Processes in Perovskite Solar Cells

Yadav

Alotaibi

Arora

et al. 2017

Adv Funct Materials

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The electronic processes occurring within the perovskite solar cells (PSCs) are strongly influenced by the nature of the organic A cations present within the inorganic framework. In this study, the impact of FA (CH(NH2)2+) and Cs+ cations on the intrinsic and interfacial properties in the FAPbBr3 and CsPbBr3 PSCs is investigated. The analysis of current density (JSC) and photovoltage (VOC) as a function of illumination intensity establishes that the interfacial charge transport is more rapid in FAPbBr3 devices. Small perturbation measurements including intensity modulated photocurrent and photovoltage spectroscopy are applied to explore the resistive and capacitive elements. Furthermore, electrochemical impedance spectroscopy measurements are found to correlate well with the photovoltaic characteristics of FAPbBr3 and CsPbBr3 PSCs. Overall, the in‐depth analysis of various phenomena occurring within the bromide PSCs allows to underline the working principle, which provides a key to optimize the device performance. The present protocol is not only valid for PSCs but can also be extended to devices based on alternative light harvesters.

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Monomolecular and Bimolecular Recombination of Electron–Hole Pairs at the Interface of a Bilayer Organic Solar Cell

Cited by 64 publications

References 56 publications

Polymer Solar Cells with 90% External Quantum Efficiency Featuring an Ideal Light‐ and Charge‐Manipulation Layer

Polymer Solar Cells with 90% External Quantum Efficiency Featuring an Ideal Light‐ and Charge‐Manipulation Layer

What is the Binding Energy of a Charge Transfer State in an Organic Solar Cell?

Influence of the Nature of A Cation on Dynamics of Charge Transfer Processes in Perovskite Solar Cells

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