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Ronald Österbacka - One of the best experts on this subject based on the ideXlab platform.

  • Bimolecular Recombination in Regioregular and Regiorandom Poly(3-Hexylthiophene):PCBM Using Photoinduced Absorption Spectroscopy
    Energy Procedia, 2012
    Co-Authors: Harri Aarnio, Ronald Österbacka
    Abstract:

    Abstract We have used photoinduced absorption (PA) spectroscopy and measured the intensity dependence on thin films of 1:1 blends of regioregular-poly(3-hexylthiophene):PCBM before and after annealing as well as on 1:1 blends of regiorandom-poly(3-hexylthiophene):PCBM. We have calculated the Bimolecular Recombination coefficients from the out-of-phase component of the photoinduced absorption. Annealing shows no change in the Bimolecular Recombination coefficients of rr-P3HT:PCBM, but the increased PA amplitude suggests that the geminate (monomolecular) Recombination is reduced. In rra-P3HT:PCBM, the Bimolecular Recombination coefficient estimated by the same method (disregarding dispersion) is significantly smaller, indicating together with a low PA amplitude that the Recombination is primarily geminate.

  • Two dimensional Langevin Recombination in regioregular poly(3-hexylthiophene)
    Applied Physics Letters, 2009
    Co-Authors: Giedrius Juška, N. Nekrašas, G. Sliaužys, Kristijonas Genevičius, Ronald Österbacka
    Abstract:

    In this work, it is shown that Recombination in regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (RRP3HT:PCBM) bulk-heterojunction solar cells is caused by the two dimensional (2D) Langevin Recombination in the lamellar structures of RRP3HT, which are formed after annealing process. Due to 2D Langevin process, Bimolecular Recombination coefficient is reduced in comparison with three dimensional Langevin case, and Bimolecular Recombination coefficient depends on the density of charge carriers n1/2. Data obtained from the different experimental techniques (charge extraction with linearly increasing voltage, integral time of flight, double injection current transients and transient absorption spectroscopy) confirms 2D Langevin Recombination in RR3PHT.

  • A review of charge transport and Recombination in polymer/fullerene organic solar cells
    Progress in Photovoltaics: Research and Applications, 2007
    Co-Authors: Almantas Pivrikas, Giedrius Juška, Niyazi Serdar Sariciftci, Ronald Österbacka
    Abstract:

    The charge carrier transport and Recombination in two types of thermally treated bulk-heterojunction solar cells is reviewed: in regioregular poly(3-hexylthiophene) (RRP3HT) mixed with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) and in the blend of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) mixed with PCBM. The charge carrier mobility and Bimolecular Recombination coefficient have been comparatively studied by using various techniques including Time-of-Flight (ToF), Charge Extraction by Linearly Increasing Voltage (CELIV), Double Injection (DI) transients, Current–Voltage (I–V) technique. It was found that the carrier mobility is at least an order of magnitude higher in RRP3HT/PCBM blends compared to MDMO-PPV/PCBM. Moreover, all used techniques demonstrate a heavily reduced charge carrier Recombination in RRP3HT/PCBM films compared to Langevin-type carrier Bimolecular Recombination in MDMO-PPV/PCBM blends. As a result of long carrier lifetimes the formation of high carrier concentration plasma in RRP3HT/PCBM blends is demonstrated and plasma extraction methods were used to directly estimate the charge carrier mobility and Bimolecular Recombination coefficients simultaneously. A weak dependence of Bimolecular Recombination coefficient on the applied electric field and temperature demonstrates that carrier Recombination is not dominated by charge carrier mobility (Langevin-type Recombination) in RRP3HT/PCBM blends. Furthermore, we found from CELIV techniques that electron mobility in RRP3HT/PCBM blends is independent on relaxation time in the experimental time window (approx. hundreds of microseconds to tens of milliseconds). This reduced carrier Bimolecular Recombination in RRP3HT/PCBM blends implies that the much longer carrier lifetimes can be reached at the same concentrations which finally results in higher photocurrent and larger power conversion efficiency of RRP3HT/PCBM solar cells. Copyright © 2007 John Wiley & Sons, Ltd.

  • Charge-carrier transport and Recombination in thin insulating films studied via extraction of injected plasma
    Physical Review B, 2006
    Co-Authors: Giedrius Juška, Gilles Dennler, Kęstutis Arlauskas, G. Sliaužys, Almantas Pivrikas, Niyazi Serdar Sariciftci, Kristijonas Genevičius, M. C. Scharber, Ronald Österbacka
    Abstract:

    We show how charge-carrier transport and Recombination in thin insulator films are directly measured using the technique of extraction of injected plasma. This technically simple technique is complementary to the well-known time-of-flight technique. We use this technique on bulk-heterojunction solar cells, where the double-injection current into an insulator is found, and we show how to use the extraction of the injected plasma to independently and simultaneously measure the charge-carrier mobility and Bimolecular Recombination coefficient in these films. A simple analytical solution to calculate the Bimolecular Recombination coefficient from an injected charge is derived. We found that the extracted charge follows a linear dependence as a function of applied voltage and saturates as a function of offset voltage, leading to the conclusion that almost all of the injected charge is extracted at high offset voltages. Therefore, we can directly measure the charge-carrier mobility and Bimolecular Recombination coefficient from the extracted charge as a function of voltage pulse duration. Moreover, the charge-carrier Bimolecular Recombination coefficient $(\ensuremath{\beta}=2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s})$ is found to be strongly reduced compared to Langevin-type coefficient, as previously shown.

  • Non-Langevin Bimolecular Recombination in low-mobility materials
    Journal of Non-Crystalline Solids, 2006
    Co-Authors: Giedrius Juška, Kęstutis Arlauskas, Jiří Stuchlík, Ronald Österbacka
    Abstract:

    Abstract We have investigated the Bimolecular Recombination coefficient ( B ) of charge carriers in low-mobility materials, in which the Langevin Recombination is reduced: inorganic a-Si:H, μc-Si:H and the organic regioregular poly(3-hexylthiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (RR-PHT/PCBM) blend. We have been using a multitude of experimental techniques, namely space-charge-limited current (SCLC), photogenerated charge carrier extraction by linearly increasing voltage (photo-CELIV) and double injection (DoI) current transient techniques for investigation of temperature and electric field dependencies of B . For RR-PHT/PCBM blends, we observed a weak dependence of B on electric field and the most significant reduction of Langevin Recombination.

Giedrius Juška - One of the best experts on this subject based on the ideXlab platform.

  • Two dimensional Langevin Recombination in regioregular poly(3-hexylthiophene)
    Applied Physics Letters, 2009
    Co-Authors: Giedrius Juška, N. Nekrašas, G. Sliaužys, Kristijonas Genevičius, Ronald Österbacka
    Abstract:

    In this work, it is shown that Recombination in regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (RRP3HT:PCBM) bulk-heterojunction solar cells is caused by the two dimensional (2D) Langevin Recombination in the lamellar structures of RRP3HT, which are formed after annealing process. Due to 2D Langevin process, Bimolecular Recombination coefficient is reduced in comparison with three dimensional Langevin case, and Bimolecular Recombination coefficient depends on the density of charge carriers n1/2. Data obtained from the different experimental techniques (charge extraction with linearly increasing voltage, integral time of flight, double injection current transients and transient absorption spectroscopy) confirms 2D Langevin Recombination in RR3PHT.

  • A review of charge transport and Recombination in polymer/fullerene organic solar cells
    Progress in Photovoltaics: Research and Applications, 2007
    Co-Authors: Almantas Pivrikas, Giedrius Juška, Niyazi Serdar Sariciftci, Ronald Österbacka
    Abstract:

    The charge carrier transport and Recombination in two types of thermally treated bulk-heterojunction solar cells is reviewed: in regioregular poly(3-hexylthiophene) (RRP3HT) mixed with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) and in the blend of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) mixed with PCBM. The charge carrier mobility and Bimolecular Recombination coefficient have been comparatively studied by using various techniques including Time-of-Flight (ToF), Charge Extraction by Linearly Increasing Voltage (CELIV), Double Injection (DI) transients, Current–Voltage (I–V) technique. It was found that the carrier mobility is at least an order of magnitude higher in RRP3HT/PCBM blends compared to MDMO-PPV/PCBM. Moreover, all used techniques demonstrate a heavily reduced charge carrier Recombination in RRP3HT/PCBM films compared to Langevin-type carrier Bimolecular Recombination in MDMO-PPV/PCBM blends. As a result of long carrier lifetimes the formation of high carrier concentration plasma in RRP3HT/PCBM blends is demonstrated and plasma extraction methods were used to directly estimate the charge carrier mobility and Bimolecular Recombination coefficients simultaneously. A weak dependence of Bimolecular Recombination coefficient on the applied electric field and temperature demonstrates that carrier Recombination is not dominated by charge carrier mobility (Langevin-type Recombination) in RRP3HT/PCBM blends. Furthermore, we found from CELIV techniques that electron mobility in RRP3HT/PCBM blends is independent on relaxation time in the experimental time window (approx. hundreds of microseconds to tens of milliseconds). This reduced carrier Bimolecular Recombination in RRP3HT/PCBM blends implies that the much longer carrier lifetimes can be reached at the same concentrations which finally results in higher photocurrent and larger power conversion efficiency of RRP3HT/PCBM solar cells. Copyright © 2007 John Wiley & Sons, Ltd.

  • Charge-carrier transport and Recombination in thin insulating films studied via extraction of injected plasma
    Physical Review B, 2006
    Co-Authors: Giedrius Juška, Gilles Dennler, Kęstutis Arlauskas, G. Sliaužys, Almantas Pivrikas, Niyazi Serdar Sariciftci, Kristijonas Genevičius, M. C. Scharber, Ronald Österbacka
    Abstract:

    We show how charge-carrier transport and Recombination in thin insulator films are directly measured using the technique of extraction of injected plasma. This technically simple technique is complementary to the well-known time-of-flight technique. We use this technique on bulk-heterojunction solar cells, where the double-injection current into an insulator is found, and we show how to use the extraction of the injected plasma to independently and simultaneously measure the charge-carrier mobility and Bimolecular Recombination coefficient in these films. A simple analytical solution to calculate the Bimolecular Recombination coefficient from an injected charge is derived. We found that the extracted charge follows a linear dependence as a function of applied voltage and saturates as a function of offset voltage, leading to the conclusion that almost all of the injected charge is extracted at high offset voltages. Therefore, we can directly measure the charge-carrier mobility and Bimolecular Recombination coefficient from the extracted charge as a function of voltage pulse duration. Moreover, the charge-carrier Bimolecular Recombination coefficient $(\ensuremath{\beta}=2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s})$ is found to be strongly reduced compared to Langevin-type coefficient, as previously shown.

  • Non-Langevin Bimolecular Recombination in low-mobility materials
    Journal of Non-Crystalline Solids, 2006
    Co-Authors: Giedrius Juška, Kęstutis Arlauskas, Jiří Stuchlík, Ronald Österbacka
    Abstract:

    Abstract We have investigated the Bimolecular Recombination coefficient ( B ) of charge carriers in low-mobility materials, in which the Langevin Recombination is reduced: inorganic a-Si:H, μc-Si:H and the organic regioregular poly(3-hexylthiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (RR-PHT/PCBM) blend. We have been using a multitude of experimental techniques, namely space-charge-limited current (SCLC), photogenerated charge carrier extraction by linearly increasing voltage (photo-CELIV) and double injection (DoI) current transient techniques for investigation of temperature and electric field dependencies of B . For RR-PHT/PCBM blends, we observed a weak dependence of B on electric field and the most significant reduction of Langevin Recombination.

  • Double injection as a technique to study charge carrier transport and Recombination in bulk-heterojunction solar cells
    Applied Physics Letters, 2005
    Co-Authors: Giedrius Juška, Attila J Mozer, Kęstutis Arlauskas, G. Sliaužys, Almantas Pivrikas, Markus C. Scharber, Niyazi Serdar Sariciftci, Ronald Österbacka
    Abstract:

    Ambipolar charge carrier mobility and Recombination in bulk-heterojunction solar cells based on the mixture of regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) has been studied using injection current transients. The experimental results demonstrate double injection with Bimolecular Recombination limiting the injection current. We found that charge carrier Bimolecular Recombination is significantly reduced compared to Langevin Recombination. We have measured the temperature and electric field dependence of the reduced Bimolecular Recombination coefficient and the results suggest that the electron and hole pathways are different and the Recombination is controlled by the probability of the carriers to meet at the polymer/PCBM interface.

Henrik Stubb - One of the best experts on this subject based on the ideXlab platform.

  • Bimolecular Recombination coefficient as a sensitive testing parameter for low-mobility solar-cell materials.
    Physical review letters, 2005
    Co-Authors: Almantas Pivrikas, Attila J Mozer, Kęstutis Arlauskas, Giedrius Juška, Henrik Stubb, Markus C. Scharber, Niyazi Serdar Sariciftci, Ronald Österbacka
    Abstract:

    Bimolecular charge carrier Recombination has been clarified in bulk-heterojunction solar cells based on a blend of regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene using the time-of-flight method. We show how Bimolecular Recombination influences the charge carrier transport, how it limits the efficiency of low-mobility solar cells, and how to estimate the Bimolecular Recombination coefficient. We found that Bimolecular Recombination in these efficient photovoltaic materials is orders of magnitude slower as compared to Langevin Recombination expected for low-mobility materials. This effect is inherent to the nanomorphology of the bicontinuous interpenetrating network creating separate pathways for electrons and holes, and paves the way for the fabrication of bulk-heterojunction solar cells where Bimolecular Recombination is not the limiting factor.

  • Optical studies of excited-state relaxation in poly(9,9-dihexylfluorene-co-benzothiadiazole)
    Physical Review B, 2003
    Co-Authors: M. Westerling, Chellappan Vijila, Ronald Österbacka, Henrik Stubb
    Abstract:

    We have studied the optical properties of poly(9,9-dihexylfluorene-co-benzothiadiazole) using absorption, photoluminescence as well, as cw and transient photoinduced absorption (PA) techniques. The PA spectrum shows a high-energy (HE) band peaked at 1.44 eV accompanied by shoulders on both sides. To study the Recombination kinetics of the photoexcitations associated with the HE band we measured the intensity and frequency dependence of the PA signal, and modeled the results by analytically solving the full Bimolecular rate equation using harmonic analysis. As an important result of these calculations we found that the experimentally observed linear intensity dependence at low pump intensities can be explained by including a monomolecular term into the rate equation, in contrast to the superlinear intensity dependence predicted for pure Bimolecular Recombination. Furthermore, the value of the monomolecular lifetime $\ensuremath{\tau}$ can directly be estimated from the ratio of the in-phase and out-of-phase signals in the linear regime, and we also show how to estimate the Bimolecular Recombination coefficient from the saturation value of the out-of-phase signal. To study the temperature dependence of the Recombination process we measured the transient decay of the HE band, and by fitting the results to the full Bimolecular rate equation we extracted the temperature dependence of the amplitude, the monomolecular lifetime, and the Bimolecular Recombination coefficient. The monomolecular lifetime decreases almost linearly with increasing temperature, and the Bimolecular Recombination coefficient has a very strong non-Arrhenius temperature dependence i.e., $\ensuremath{\beta}={\ensuremath{\beta}}_{0}\mathrm{exp}[{(T/T}_{0}{)}^{2}],$ with ${\ensuremath{\beta}}_{0}=1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}{\mathrm{cm}}^{3}/\mathrm{s}$ and a characteristic temperature ${T}_{0}=82\mathrm{K}.$ A model for this unusual temperature dependence is proposed.

  • Bimolecular Recombination in regiorandom poly(3-hexylthiophene)
    2002
    Co-Authors: M. Westerling, Chellappan Vijila, Ronald Österbacka, Henrik Stubb
    Abstract:

    Using cw and transient photoinduced absorption (PA) techniques we study the photoexcitation dynamics in the ms time regime, in thin films of regiorandom poly(3-hexylthiophene). The PA spectrum shows a high energy band (HE) peaked at 1.46 eV and a low energy band (LE) at 0.5 eV. The PA dependence on pump intensity and modulation frequency is modeled by analytically solving the full Bimolecular rate equation using harmonic analysis. As an important result of these calculations we found that in the steady-state limit (i.e., xsB � 1), the out-of-phase PA signal saturates and becomes independent of pump intensity. This gives rise to a new possibility of directly estimating the Bimolecular Recombination coefficient b from the saturation value of the out-of-phase PA signal at high pump intensities. The transient PA decay of the HE band shows two components having different relaxation times. The PA decay of the HE band is mainly dominated by the fast component, which is attributed to a Bimolecular Recombination process in good agreement with the result from the cw measurements, together yielding a Bimolecular Recombination constant b ¼ 1:6 � 1:4 � 10 � 14 cm 3 =s. 2002 Elsevier Science B.V. All rights reserved.

  • Charge carrier mobility in Langmuir-Blodgett films of poly(3-hexylthiophene)
    Synthetic Metals, 1999
    Co-Authors: Giedrius Juška, Kęstutis Arlauskas, Ronald Österbacka, Henrik G.o. Sandberg, Henrik Stubb
    Abstract:

    Abstract The tendency to saturation in the collected charge as a function of light intensity in Langmuir-Blodgett films of poly(3-hexylthiophene) (PHT) has been studied. The tendency to saturation can have two reasons; that the space charge limited current regime has been reached, or influence of very fast Bimolecular Recombination. We have studied these two cases, and we conclude that Bimolecular Recombination is a probable cause for the tendency to saturation. The hole mobility in PHT can therefore possibly be estimated as high as 1 cm 2 /Vs in the initial stage after photoexcitation.

Almantas Pivrikas - One of the best experts on this subject based on the ideXlab platform.

  • Molecular weight dependent Bimolecular Recombination in organic solar cells
    The Journal of chemical physics, 2014
    Co-Authors: Bronson Philippa, Martin Stolterfoht, Ronald D. White, Marrapan Velusamy, Paul L. Burn, Paul Meredith, Almantas Pivrikas
    Abstract:

    Charge carrier Recombination is studied in operational organic solar cells made from the polymer:fullerene system PCDTBT:PC71BM (poly[N-9"-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] : [6,6]-phenyl-C$_{70}$-butyric acid methyl ester). A newly developed technique High Intensity Resistance dependent PhotoVoltage (HI-RPV) is presented for reliably quantifying the Bimolecular Recombination coefficient independently of variations in experimental conditions, thereby resolving key limitations of previous experimental approaches. Experiments are performed on solar cells of varying thicknesses and varying polymeric molecular weights. It is shown that solar cells made from low molecular weight PCDTBT exhibit Langevin Recombination, whereas suppressed (non-Langevin) Recombination is found in solar cells made with high molecular weight PCDTBT.

  • Injected charge extraction by linearly increasing voltage for Bimolecular Recombination studies in organic solar cells
    Applied Physics Letters, 2012
    Co-Authors: Ardalan Armin, Paul L. Burn, Marrapan Velusamy, Paul Meredith, Almantas Pivrikas
    Abstract:

    We present a technique called “injected charge extraction by linearly increasing voltage” (i-CELIV) and apply it to evaluate Bimolecular Recombination in organic solar cells. The experimental setup is straightforward requiring no laser or optical-electrical pulse synchronization. The applicability of the method is discussed and non-Langevin Recombination in a model poly(3-n-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PC60BM) solar cell is quantified and confirmed. Further, Langevin Recombination in the low optical gap high efficiency blend, poly[2,6-(4,4-bis-{2-ethylhexyl}-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]:phenyl-C71-butyric acid methyl ester is reported using i-CELIV.

  • A review of charge transport and Recombination in polymer/fullerene organic solar cells
    Progress in Photovoltaics: Research and Applications, 2007
    Co-Authors: Almantas Pivrikas, Giedrius Juška, Niyazi Serdar Sariciftci, Ronald Österbacka
    Abstract:

    The charge carrier transport and Recombination in two types of thermally treated bulk-heterojunction solar cells is reviewed: in regioregular poly(3-hexylthiophene) (RRP3HT) mixed with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) and in the blend of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) mixed with PCBM. The charge carrier mobility and Bimolecular Recombination coefficient have been comparatively studied by using various techniques including Time-of-Flight (ToF), Charge Extraction by Linearly Increasing Voltage (CELIV), Double Injection (DI) transients, Current–Voltage (I–V) technique. It was found that the carrier mobility is at least an order of magnitude higher in RRP3HT/PCBM blends compared to MDMO-PPV/PCBM. Moreover, all used techniques demonstrate a heavily reduced charge carrier Recombination in RRP3HT/PCBM films compared to Langevin-type carrier Bimolecular Recombination in MDMO-PPV/PCBM blends. As a result of long carrier lifetimes the formation of high carrier concentration plasma in RRP3HT/PCBM blends is demonstrated and plasma extraction methods were used to directly estimate the charge carrier mobility and Bimolecular Recombination coefficients simultaneously. A weak dependence of Bimolecular Recombination coefficient on the applied electric field and temperature demonstrates that carrier Recombination is not dominated by charge carrier mobility (Langevin-type Recombination) in RRP3HT/PCBM blends. Furthermore, we found from CELIV techniques that electron mobility in RRP3HT/PCBM blends is independent on relaxation time in the experimental time window (approx. hundreds of microseconds to tens of milliseconds). This reduced carrier Bimolecular Recombination in RRP3HT/PCBM blends implies that the much longer carrier lifetimes can be reached at the same concentrations which finally results in higher photocurrent and larger power conversion efficiency of RRP3HT/PCBM solar cells. Copyright © 2007 John Wiley & Sons, Ltd.

  • Charge-carrier transport and Recombination in thin insulating films studied via extraction of injected plasma
    Physical Review B, 2006
    Co-Authors: Giedrius Juška, Gilles Dennler, Kęstutis Arlauskas, G. Sliaužys, Almantas Pivrikas, Niyazi Serdar Sariciftci, Kristijonas Genevičius, M. C. Scharber, Ronald Österbacka
    Abstract:

    We show how charge-carrier transport and Recombination in thin insulator films are directly measured using the technique of extraction of injected plasma. This technically simple technique is complementary to the well-known time-of-flight technique. We use this technique on bulk-heterojunction solar cells, where the double-injection current into an insulator is found, and we show how to use the extraction of the injected plasma to independently and simultaneously measure the charge-carrier mobility and Bimolecular Recombination coefficient in these films. A simple analytical solution to calculate the Bimolecular Recombination coefficient from an injected charge is derived. We found that the extracted charge follows a linear dependence as a function of applied voltage and saturates as a function of offset voltage, leading to the conclusion that almost all of the injected charge is extracted at high offset voltages. Therefore, we can directly measure the charge-carrier mobility and Bimolecular Recombination coefficient from the extracted charge as a function of voltage pulse duration. Moreover, the charge-carrier Bimolecular Recombination coefficient $(\ensuremath{\beta}=2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s})$ is found to be strongly reduced compared to Langevin-type coefficient, as previously shown.

  • Double injection as a technique to study charge carrier transport and Recombination in bulk-heterojunction solar cells
    Applied Physics Letters, 2005
    Co-Authors: Giedrius Juška, Attila J Mozer, Kęstutis Arlauskas, G. Sliaužys, Almantas Pivrikas, Markus C. Scharber, Niyazi Serdar Sariciftci, Ronald Österbacka
    Abstract:

    Ambipolar charge carrier mobility and Recombination in bulk-heterojunction solar cells based on the mixture of regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) has been studied using injection current transients. The experimental results demonstrate double injection with Bimolecular Recombination limiting the injection current. We found that charge carrier Bimolecular Recombination is significantly reduced compared to Langevin Recombination. We have measured the temperature and electric field dependence of the reduced Bimolecular Recombination coefficient and the results suggest that the electron and hole pathways are different and the Recombination is controlled by the probability of the carriers to meet at the polymer/PCBM interface.

James R. Durrant - One of the best experts on this subject based on the ideXlab platform.

  • Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
    The Journal of Physical Chemistry C, 2017
    Co-Authors: Ardalan Armin, James R. Durrant, Safa Shoaee
    Abstract:

    Despite the myriad of organic donor:acceptor materials, only few systems have emerged in the life of organic solar cells to exhibit considerable reduced Bimolecular Recombination, with respect to the random encounter rate given by the Langevin equation. Monte Carlo simulations have revealed that the rate constant of the formation of electron–hole bound states depends on the random encounter of opposite charges and is nearly given by the Langevin equation for the domain sizes relevant to efficient bulk heterojunction systems. Recently, three studies suggested that charge transfer states dissociating much faster than their decay rate to the ground state, can result in reduced Bimolecular Recombination by lowering the Recombination rate to the ground state as a loss pathway. A separate study identified another loss pathway and suggested that forbidden back electron transfer from triplet charge transfer states to triplet excitons is a key to achieving reduced Recombination. Herein we further explain the reduc...

  • Transient Absorption Studies of Bimolecular Recombination Dynamics in Polythiophene/Fullerene Blend Films
    The Journal of Physical Chemistry C, 2009
    Co-Authors: Tracey M. Clarke, Fiona C. Jamieson, James R. Durrant
    Abstract:

    Bimolecular Recombination, an important loss mechanism in organic solar cells, has been investigated using transient absorption spectroscopy for poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) films and analogues of these components. Data are analyzed as a function of blend composition, postdeposition thermal annealing, and excitation density. Comparison of transient spectra for P3HT:PCBM films with analogous films employing P3HS and PC70BM allows the assignment of the photoinduced absorption features. These decay dynamics are analyzed on the nanosecond to millisecond time scales and are shown to be in excellent agreement with a Bimolecular Recombination model in the presence of an exponential distribution of localized (trap) states. Thermal annealing results in an acceleration of these decay dynamics, which is assigned to a reduction in the depth of the trap states and correlated with an increase in film crystallinity. The decay dynamics are analyzed to obtain an effective r...

  • transient absorption studies of Bimolecular Recombination dynamics in polythiophene fullerene blend films
    Journal of Physical Chemistry C, 2009
    Co-Authors: Tracey M. Clarke, Fiona Jamieson, James R. Durrant
    Abstract:

    Bimolecular Recombination, an important loss mechanism in organic solar cells, has been investigated using transient absorption spectroscopy for poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) films and analogues of these components. Data are analyzed as a function of blend composition, postdeposition thermal annealing, and excitation density. Comparison of transient spectra for P3HT:PCBM films with analogous films employing P3HS and PC70BM allows the assignment of the photoinduced absorption features. These decay dynamics are analyzed on the nanosecond to millisecond time scales and are shown to be in excellent agreement with a Bimolecular Recombination model in the presence of an exponential distribution of localized (trap) states. Thermal annealing results in an acceleration of these decay dynamics, which is assigned to a reduction in the depth of the trap states and correlated with an increase in film crystallinity. The decay dynamics are analyzed to obtain an effective r...

  • Charge extraction analysis of charge carrier densities in a polythiophene/fullerene solar cell: Analysis of the origin of the device dark current
    Applied Physics Letters, 2008
    Co-Authors: Christopher G. Shuttle, Andrea Maurano, R. W. Hamilton, Brian C. O'regan, J. C. De Mello, James R. Durrant
    Abstract:

    We demonstrate the use of a simple charge extraction measurement to determine the charge carrier densities n in annealed poly(3-hexylthiophene):methanofullerene solar cells under operating conditions. By applying charge extraction to the device under forward bias in the dark (Jdark), we find Jdark∝n2.6. This dependence on charge density is the same as that we find for Bimolecular Recombination losses observed in such devices under irradiation at open circuit, suggesting that the dark current originates from Bimolecular Recombination at the polymer/fullerene interface.