Electron diffusion in polymer:fullerene bulk heterojunctions

Quist, Pieter A. C.; Savenije, Tom J.; Schins, Juleon M.; Kroeze, Jessica E.; Rijkers, Paul A.; Siebbeles, Laurens D. A.

doi:10.1103/physrevb.75.195317

Cited by 13 publications

(11 citation statements)

References 30 publications

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“…A reason for this might be that for recombination the charge carriers have to move out of the crystalline domains, which is an energetically uphill process. This is in agreement with previous photoconductance measurements on blends of P3HT:PCBM 11,45 .…”

Section: Resultssupporting

confidence: 93%

Observation of bi-polarons in blends of conjugated copolymers and fullerene derivatives

Savenije

Sperlich

Kraus

et al. 2011

Phys. Chem. Chem. Phys.

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From a fundamental and application point of view it is of importance to understand how charge carrier generation and transport in a conjugated polymer (CP):fullerene blend are affected by the blend morphology. In this work light-induced electron spin resonance (LESR) spectra and transient ESR response signals are recorded on non-annealed and annealed blend layers consisting of alkyl substituted thieno[3,2-b]thiophene copolymers (pATBT) and the soluble fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) at temperatures ranging from 10 to 180 K. Annealing of the blend sample leads to a reduction of the steady state concentration of light-induced PCBM anions within the blend at low temperatures (T = 10 K) and continuous illumination. This is explained on the basis of the reducing interfacial area of the blend composite on annealing, and the high activation energy for electron diffusion in PCBM blends leading to trapped electrons near the interface with the CP. As a consequence, these trapped electrons block consecutive electron transfer from an exciton on a CP to the PCBM domain, resulting in a relatively low concentration charge carriers in the annealed blend. Analysis of the transient ESR data allows us to conclude that in annealed samples diamagnetic bi-polaronic states on the CPs are generated at low temperature. The formation of these states is related to the generation and interaction of multiple positive polarons in the large crystalline polymer domains present in the annealed sample.

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Section: Resultssupporting

confidence: 93%

Observation of bi-polarons in blends of conjugated copolymers and fullerene derivatives

Savenije

Sperlich

Kraus

et al. 2011

Phys. Chem. Chem. Phys.

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“…The 3D AFM image of P(VDF‐TrFE) NPs on top of PCDTBT:PC 70 BM film is shown in Figure b. In polymer:PCBM bulk heterojunction solar cells, electron diffusion lengths ranging from 40–130 nm have been reported, depending on the property of the polymer and content of PCBM . Small P(VDF‐TrFE) NPs of 60–90 nm were selected as the ferroelectric interlayer so that most photogenerated carriers can go around the insulated NPs by diffusion and be collected by the electrode.…”

Section: Comparison Of Fe‐opv Performances With Different Ferroelectrmentioning

confidence: 99%

“…To address this issue, we used piezoresponse force microscopy (PFM) to directly measure the piezoelectric hysteresis loops of individual NPs. [ 34 ] Small P(VDF-TrFE) NPs of 60-90 nm were selected as the ferroelectric interlayer so that most photogenerated carriers can go around the insulated NPs by diffusion and be collected by the electrode. It is clearly seen that the polarization of the refl uxed P(VDF-TrFE) NPs is switched by the voltage bias supplied by the PFM tip, confi rming the ferroelectricity of the P(VDF-TrFE) NPs.…”

mentioning

confidence: 99%

Synthesis and Application of Ferroelectric P(VDF‐TrFE) Nanoparticles in Organic Photovoltaic Devices for High Efficiency

Xiao

Dong

Sharma

et al. 2013

Advanced Energy Materials

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The power conversion effi ciency (PCE) of organic photovoltaic devices has entered the over 10% era. [ 1,2 ] Interlayers between the organic active layer and the electrodes play important roles in achieving high effi ciencies. Many types of interlayers have been reported, such as metal oxides, [3][4][5] polymer electrolytes, [ 6,7 ] and low-work-function metals. [ 8 ] Generally, these interlayers have the function of bridging the Fermi energy of the electrode and the energy levels of the organic semiconductor and increasing the built-in electric fi eld in the devices. [ 6 ] Recently, we reported a new category of air stable material, ferroelectric polymer poly(vinylidenefl uoride-trifl uoroethylene) (P(VDF-TrFE)), as a universal interlayer, which has tunable and highdensity, aligned dipoles controlled by the external applied bias. [ 9 ] This ferroelectric interlayer can effectively increase or decrease the work function of any electrode to serve as both anode and cathode due to the switchable dipole direction. A strong electric fi eld can be induced in the semiconducting polymers by the unscreened polarization charges of the P(VDF-TrFE), which has been demonstrated to improve the PCE of several types of organic photovoltaic cells (OPVs) to unprecedented values, superior to many other methods. In our previous studies, it was also shown that the polarization of P(VDF-TrFE) on the organic semiconductor fi lms is stable [ 10,11 ] and the surface charges are not screened by photogenerated carriers. [ 10 ] A crystalline β -phase P(VDF-TrFE) fi lm is needed to ensure its ferroelectricity. [ 10 ] Langmuir-Blodgett (LB) deposition is an excellent method for forming highly crystalline P(VDF-TrFE) fi lm as thin as 1 nm. [ 9 ] However, P(VDF-TrFE) LB fi lms generally need a thermal annealing process after the deposition to convert them into the ferroelectric phase at above the Curie temperature. In our previous studies, the P(VDF-TrFE 70:30) LB fi lms were annealed at 135 °C for half an hour to completely convert them to the ferroelectric phase. [ 9,11 ] However, this high temperature thermal annealing process is not compatible with the fabrication process of many high-performance, low bandgap polymer-based OPV devices, such as thieno3,4-b-thiophene/ benzodithiophene (PTBs) [ 6,12,13 ] and poly N -9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole) (PCDTBT). [14][15][16] These polymers are generally heated at 70 °C or vacuumed to remove solvent in the spun fi lms. [ 14 ] A high-temperature annealing at 135 °C will signifi cantly reduce the PCEs of these polymer-based OPVs due to over annealing, causing overly large 6,6-phenyl-C 61 -butyric acid methyl ester (PCBM) or polymer nanodomains. [ 17 ] In addition, it is diffi cult to control the morphology of P(VDF-TrFE) LB fi lms after thermal annealing. [ 18 ] Appropriate P(VDF-TrFE) size of the nanoislands and spacing between them is critically important so that the photogenerated charges can be fully extracted rather than blocked by the large, t...

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“…Furthermore, it has been found that fullerenes crystallize in some solid blends prepared from organic solvents such as benzene, chlorobenzene (CB), ortho-dichlorobenzene (oDCB), and chloroform at high concentration or following annealing treatment. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] The crystallite formation of fullerenes can have a significant effect on the properties of blend films because the properties of crystalline fullerenes may be different from those of amorphous fullerene molecules. For instance, the band gaps (E g ) of both C 60 and its derivative phenyl-C 61 -butyric-acid-methyl-ester (PCBM) crystals are lower when compared to those of the isolated C 60 and PCBM molecules.…”

Section: Introductionmentioning

confidence: 99%

“…25,26 Some previous studies 14,16,17,20,21,23 have also shown that devices based on poly-3-hexylthiophene (P3HT) and PCBM blends display a better performance (e.g., a large increase in photocurrent and carrier lifetime) following thermal annealing which alters the fraction of amorphous and microcrystalline PCBM domains, with the formation of PCBM nano-crystalline domains that are crucial for high PCEs. 14,16,27 To date, a large number of studies both in experimental implementations [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] and in theoretical aspects 24,[44][45][46]…”

Section: Introductionmentioning

confidence: 99%

Linear-scaling density functional simulations of the effect of crystallographic structure on the electronic and optical properties of fullerene solvates

Han

Boschetto

Krompiec

et al. 2017

Phys. Chem. Chem. Phys.

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In this work, the crystal properties, HOMO and LUMO energies, band gaps, density of states, as well as the optical absorption spectra of fullerene C and its derivative phenyl-C-butyric-acid-methyl-ester (PCBM) co-crystallised with various solvents such as benzene, biphenyl, cyclohexane, and chlorobenzene were investigated computationally using linear-scaling density functional theory with plane waves as implemented in the ONETEP program. Such solvates are useful materials as electron acceptors for organic photovoltaic (OPV) devices. We found that the fullerene parts contained in the solvates are unstable without solvents, and the interactions between fullerene and solvent molecules in C and PCBM solvates make a significant contribution to the cohesive energies of solvates, indicating that solvent molecules are essential to keep C and PCBM solvates stable. Both the band gap (E) and the HOMO and LUMO states of C and PCBM solvates are mainly determined by the fullerene parts contained in solvates. Chlorobenzene- and ortho-dichlorobenzene-solvated PCBM are the most promising electron-accepting materials among these solvates for increasing the driving force for charge separation in OPVs due to their relatively high LUMO energies. The UV-Vis absorption spectra of solvent-free C and PCBM crystals in the present work are similar to those of C and PCBM thin films shown in the literature. Changes in the absorption spectra of C solvates relative to the solvent-free C crystal are more significant than those of PCBM solvates due to the weaker effect of solvents on the π-stacking interactions between fullerene molecules in the latter solvates. The main absorptions for all C and PCBM crystals are located in the ultraviolet (UV) region.

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Electron diffusion in polymer:fullerene bulk heterojunctions

Cited by 13 publications

References 30 publications

Observation of bi-polarons in blends of conjugated copolymers and fullerene derivatives

Observation of bi-polarons in blends of conjugated copolymers and fullerene derivatives

Synthesis and Application of Ferroelectric P(VDF‐TrFE) Nanoparticles in Organic Photovoltaic Devices for High Efficiency

Linear-scaling density functional simulations of the effect of crystallographic structure on the electronic and optical properties of fullerene solvates

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