Techniques for characterization of charge carrier mobility in organic semiconductors

Kokil, Akshay; Yang, Ke; Kumar, Jayant

doi:10.1002/polb.23103

Cited by 152 publications

(139 citation statements)

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“…12,13 The use of conjugated small molecular species such as the oligoacenes (anthracene, pentacene, tetracene, and rubrene) has provided the experimentalist an avenue to grow crystals that are of high purity and that possess a high degree of structural order. [14][15][16][17][18] Two commonly used techniques for determining charge carrier mobilities in oligoacenes are field-effect transistor (FET) measurements 17,19,20 and time-of-flight (TOF) measurements. 19,21,22 FET measurements probe transport in the a-b plane at or near the surface of the crystal.…”

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confidence: 99%

“…[14][15][16][17][18] Two commonly used techniques for determining charge carrier mobilities in oligoacenes are field-effect transistor (FET) measurements 17,19,20 and time-of-flight (TOF) measurements. 19,21,22 FET measurements probe transport in the a-b plane at or near the surface of the crystal. TOF measurements are routinely used for measuring mobilities through the bulk of the material, typically corresponding to the c-lattice parameter of oligoacenes.…”

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confidence: 99%

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Temperature dependent c-axis hole mobilities in rubrene single crystals determined by time-of-flight

Pundsack

Haugen

Johnstone

et al. 2015

Applied Physics Letters

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Hole mobilities (μ) in rubrene single crystals (space group Cmca) along the crystallographic c-axis have been investigated as a function of temperature and applied electric field by the time-of-fight method. Measurements demonstrate an inverse power law dependence on temperature, namely, μ=μ0T−n with n = 1.8, from room temperature down to 180 K. At 296 K, the average value of μ was found to be 0.29 cm2/Vs increasing to an average value of 0.70 cm2/Vs at 180 K. Below 180 K a decrease in mobility is observed with further cooling. Overall, these results confirm the anisotropic nature of transport in rubrene crystals as well as the generality of the inverse power law temperature dependence that is observed for field effect mobility measurements in the a-b crystal plane.

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confidence: 99%

mentioning

confidence: 99%

Temperature dependent c-axis hole mobilities in rubrene single crystals determined by time-of-flight

Pundsack

Haugen

Johnstone

et al. 2015

Applied Physics Letters

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“…The mobility was measured by the space charge limited current (SCLC) method [81] as described in chapter 2. The relative dielectric constant ε r was extracted from the geometrical capacitance of the solar cells.…”

Section: Polaron Pair Dissociation Probabilitymentioning

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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“…This limits the mobility of the device and also requires different measurement techniques. To date, a few techniques to measure mobility in thin film devices have been reported [18,19]. These are briefly described below.…”

Section: Mobility Measurements In Opvsmentioning

confidence: 99%

“…By carefully choosing electrodes with the required work functions to guarantee an SCLC regime, the solar device can be probed for dark J-V characteristics. Using the SCLC equations above, the best fit provides the mobility [19].…”

Section: Space Charge Limited Current (Sclc)mentioning

confidence: 99%

Determination of Carrier Mobility for Thin-Film Organic and Hybrid Solar Cells through Transient Photoconductivity

Sachdeva¹

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Transient photoconductivity is widely used to study decay characteristics of organic solar cells. For thick devices (> 1μm), the Time of Flight (TOF) technique is one such transient technique that is used to extract carrier mobility. TOF determines the amount of time it takes for photon-generated charge carriers to travel from one electrode to another in order to calculate mobility. However, in thin film organic semiconductors, TOF has shown to be difficult to implement due RC time constant limitations and generation of charge throughout the device.Recently, transient photoconductivity has been used to measure carrier mobilities in organic thin-film solar cells that reproduced numbers found in literature. To confirm the validity of transient photoconductivity as a means to find mobility, experiments were performed on poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methylester (PCBM) solar cells. The results were compared with Space Charge Limited Current mobility numbers for the same device. Transient photoconductivity was found to be a sound technique under certain conditions. The transient photoconductivity technique was further used to calculate carrier mobility for P3HT:Cadmium Selenide (CdSe) hybrid solar cells, with results agreeing with those found in literature.ii

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Techniques for characterization of charge carrier mobility in organic semiconductors

Cited by 152 publications

References 130 publications

Temperature dependent c-axis hole mobilities in rubrene single crystals determined by time-of-flight

Temperature dependent c-axis hole mobilities in rubrene single crystals determined by time-of-flight

Photocurrent Limiting Mechanisms in Organic Bulk Heterojunction Solar Cells

Determination of Carrier Mobility for Thin-Film Organic and Hybrid Solar Cells through Transient Photoconductivity

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