Accounting for Interference, Scattering, and Electrode Absorption to Make Accurate Internal Quantum Efficiency Measurements in Organic and Other Thin Solar Cells

Burkhard, George F.; Hoke, Eric T.; McGehee, Michael D.

doi:10.1002/adma.201000883

Cited by 669 publications

(636 citation statements)

References 25 publications

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“…1a-d, which show the device structure, photo-generated carrier distribution profile, and the EQE and absorption spectra of the photo-active layers, respectively. Although the figures are schematics for illustrative purposes, knowledge of the optical constants (n and k see Methods) of all layers in the diode structure allows one to accurately simulate the actual optical field distributions, EQE and absorption using a transfer matrix analysis 29,39,40 . In this case the PCDTBT:PC70BM optical constants are used to demonstrate the concept.…”

Section: Resultsmentioning

confidence: 99%

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

et al. 2015

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Spectrally selective light detection is vital for full-colour and near-infrared (NIR) imaging and machine vision. This is not possible with traditional broadband-absorbing inorganic semiconductors without input filtering, and is yet to be achieved for narrowband absorbing organic semiconductors. We demonstrate the first sub-100 nm full-width-at-half-maximum visible-blind red and NIR photodetectors with state-of-the-art performance across critical response metrics. These devices are based on organic photodiodes with optically thick junctions. Paradoxically, we use broadband-absorbing organic semiconductors and utilize the electro-optical properties of the junction to create the narrowest NIR-band photoresponses yet demonstrated. In this context, these photodiodes outperform the encumbent technology (input filtered inorganic semiconductor diodes) and emerging technologies such as narrow absorber organic semiconductors or quantum nanocrystals. The design concept allows for response tuning and is generic for other spectral windows. Furthermore, it is materialagnostic and applicable to other disordered and polycrystalline semiconductors.

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Section: Resultsmentioning

confidence: 99%

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

et al. 2015

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“…As shown in Fig. 8-1(b), the IQE exhibits larger variations for above bandgap illumination than inorganic solar cells and is consistent with previous reports that IQE is not a consistant value for all the wavelengths [121]. This is maybe due to surface scattering, the accuracy of the active layer thickness measurement, and the uniformity of the films.…”

Section: I-v Curve Simulation Including R S and R Shsupporting

confidence: 78%

“…Since it is not at 640 nm, we encounter a similar issue. There are also other factors, such as surface scattering, the accuracy of the active layer thickness measurement, and the uniformity of the films that may affect the results [121].…”

Section: I-v Curve Simulation Including R S and R Shmentioning

confidence: 99%

Photocurrent Limiting Mechanisms in Organic Bulk Heterojunction Solar Cells

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As we use more energy as a society, there is a greater need to become less reliant on non-renewable energy sources. Photovoltaics (PV), as a method of harvesting sunlight and converting it into electricity, provide a potential way of producing clean renewable energy.Organic bulk heteojunction (BHJ) solar cells featured with low-cost, large-area and thin-film manufacture, have become more viable with the recent demonstration with power conversion efficiencies (PCE) as high as10.7%. However, there is still a room for further improvement to reach the thermodynamic PCE limit of ~22%. For organic BHJ solar cells, the efficiency is essentially limited by the low short-circuit current density, which is determined by four sequential steps that are necessary to transform incident photons to free charge carriers. These steps are photo absorption and exciton formation, exciton diffusion, polaron pair dissociation and free polaron collection. In order to know the extent to which each of these steps limits the efficiency, a systematic study to analyze the limiting mechanisms is beneficial.In this work, we report approaches that are capable of providing insight into these processes by applying several complementary experimental techniques and theoretical calculations. The material system that are studied are poly(3-hexylthiophene) (P3HT): Therefore, it is quite intrigue to explore the reasons behind that.For absorption, the optical transfer-matrix theory is applied on the multi-thinlayer structure of organic BHJ solar cells. The complex refractive index is extracted.Meanwhile, the optical electric field and the absorption efficiency are calculated and iii AcknowledgementThe Ph.D study is a strict but a joyful scientific training. To make through it, I'd like to thank to the people who gave me tremendous support in these years.First and foremost I would like to thank my supervisor, Dr. Joe C. Campbell, for his patient guidance, continual support and encouragement during my Ph.D study. I learned a lot from him, not only about how to tackle the experimental/theoretical problems, but also about the vision, the presentation skills, and the way to keep a good relationship with your collaborators. I also appreciate the research freedom that Dr. Joe C. Campbell gave to me, which allows me to deliberate, to try and to pursuit without worrying.

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“…To address this issue, we calculated the 1D laser intensity profile for the GaN-on-SiC epilayer structure described in Section III. A (30 nm Al0.25Ga0.75N, 1.2 µm GaN, 100 nm AlN, and 100 µm 4H-SiC) using the optical transfer matrix formalism [56] and indices of refraction at 488 nm reported in the literature [57]- [58]. As a conservative approximation, we also set the absorption coefficient of each layer equal to = 0.1 µm -1 .…”

Section: Non-uniform Optical Samplingmentioning

confidence: 99%

Contributed Review: Experimental characterization of inverse piezoelectric strain in GaN HEMTs via micro-Raman spectroscopy

Bagnall

Wang

2016

Review of Scientific Instruments

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Micro-Raman thermography is one of the most popular techniques for measuring local temperature rise in gallium nitride (GaN) high electron mobility transistors (HEMTs) with high spatial and temporal resolution. However, accurate temperature measurements based on changes in the Stokes peak positions of the GaN epitaxial layers requires properly accounting for the stress and/or strain induced by the inverse piezoelectric effect. It is common practice to use the pinched OFF state as the unpowered reference for temperature measurements because the vertical electric field in the GaN buffer that induces inverse piezoelectric stress/strain is relatively independent of the gate bias. Although this approach has yielded temperature measurements that agree with those derived from the Stokes/anti-Stokes ratio and thermal models, there has been significant difficulty in quantifying the mechanical state of the GaN buffer in the pinched OFF state from changes in the Raman spectra. In this paper, we review the experimental technique of micro-Raman thermography and derive expressions for the detailed dependence of the Raman peak positions on strain, stress, and electric field components in wurtzite GaN. We also use a combination of semiconductor device modeling and electro-mechanical modeling to predict the stress and strain induced by the inverse piezoelectric effect. Based on the insights gained from our electromechanical model and the best values of material properties in the literature, we analyze changes in the E2 high and A1 (LO) Raman peaks and demonstrate that there are major quantitative discrepancies between measured and modeled values of inverse piezoelectric stress and strain. We examine many of the hypotheses offered in the literature for these discrepancies but conclude that 2 none of them satisfactorily resolves these discrepancies. Further research is needed to determine whether the electric field along the -axis could be affecting the phonon frequencies apart from the inverse piezoelectric effect in wurtzite GaN, which has been predicted theoretically in zinc blende gallium arsenide (GaAs).

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Accounting for Interference, Scattering, and Electrode Absorption to Make Accurate Internal Quantum Efficiency Measurements in Organic and Other Thin Solar Cells

Cited by 669 publications

References 25 publications

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

Photocurrent Limiting Mechanisms in Organic Bulk Heterojunction Solar Cells

Contributed Review: Experimental characterization of inverse piezoelectric strain in GaN HEMTs via micro-Raman spectroscopy

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