Effects of cathode buffer layers on the efficiency of bulk-heterojunction solar cells

Chang, Che-Ming; Lin, Chi‐Feng; Chiou, Jian-Ming; Ho, Tzung-Han; Tai, Yian; Lee, Jiun-Haw; Chen, Yang‐Fang; Wang, Juen-Kai; Chen, Li‐Chyong; Chen, Kuei‐Hsien

doi:10.1063/1.3456530

Cited by 59 publications

(46 citation statements)

References 27 publications

(25 reference statements)

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“…The inclusion of these interlayers is supposed to largely modify the interface electronic ARTICLE structure which enhances the device performance. We have studied here the effect of LiF, 35 bathocuproine BCP, 36 and evaporated C 60 thin layers on interfacial properties as displayed in the MottÀSchottky characteristics. Details on the deposition methods of these interlayers can be obtained in Supporting Information.…”

Section: Experimental Determination Of Flat-band Values and Dipole Lamentioning

confidence: 99%

How the Charge-Neutrality Level of Interface States Controls Energy Level Alignment in Cathode Contacts of Organic Bulk-Heterojunction Solar Cells

et al. 2012

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In organic photovoltaic devices, outer interface structures play a significant role in establishing optimal contact conditions for efficient extraction (or blocking) of charge carriers. Buffer layers of different nature are currently employed to enhance both power conversion efficiency (PCE) and cell stability by improving contact performance. Several materials have been explored to enhance the electron selectivity of the cathode contact: alkali metal compounds (LiF, etc.), metal oxides (TiO x , ZnO, etc.), and low molecular weight organic compounds have been reported to contribute to the overall PCE and solar cell lifetime, as reviewed in recent reports.1À3 Among those approaches, the effect of the dipole moment associated with self-assembled monolayers (SAM) attached to the interface, which alter the energy level alignment between the cathode metal and the bulk of the blend, 4 is particularly interesting, as well as the inclusion of conjugated polyelectrolyte interlayers. 5 In all of these cases, the energy shift induced by the charge dipole built up at interface layers enables the use of air-stable high work function metals. It is then inferred that electrostatic mechanisms occurring at the nanometer scale, both in the active layer bulk and at interfaces, have a great influence on the overall device operation. 6,7 Interface dipole layers are regarded as a determining ingredient of the metal/organic contact equilibration. 8À12 Several models have been proposed to account for the energy level alignment at interfaces, depending on the degree of interaction between the metal contact and the deposited organic layer. When the chemical interaction between the metal and contacting conjugated molecules or polymers is not negligible, it is expected that molecules attached to the metal surface undergo both a shift and a broadening of their molecular energy levels. Energy distribution of the attached molecules should be modeled by a specific interfacial density of states (IDOS) which differs from that encountered in the bulk of the organic layer. The situation is

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Section: Experimental Determination Of Flat-band Values and Dipole Lamentioning

confidence: 99%

How the Charge-Neutrality Level of Interface States Controls Energy Level Alignment in Cathode Contacts of Organic Bulk-Heterojunction Solar Cells

et al. 2012

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“…The use of interlayers circumvents the direct contact between the photoactive donor (polymer or small molecule) and electrodes where high densities of carrier traps and interface dipoles can hinder efficient charge collection. Consequently, a significant effort in interfacial engineering has developed using metal oxides (MoO 3 , CsCO 3 , TiO x , NiO, WO 3 , V 2 O 5 and ZnO, Ca)12131415161718, LiF1920, bathocuproine (BCP)2122, and self-assembled monolayers (SAMs)23. Although several metal oxides have been studied as anode interlayer or hole transport layer (HTL), poly (3,4-ethylene dioxythiophene):(polystyrene sulfonic acid) (PEDOT:PSS) is most commonly used as the anode interlayer or hole transporting layer (HTL) due to its high work function and compatibility with ITO.…”

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confidence: 99%

Barium: An Efficient Cathode Layer for Bulk-heterojunction Solar Cells

Gupta

Kyaw

Wang

et al. 2013

Sci Rep

368

324

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We report Barium (Ba) cathode layer for bulk-heterojunction solar cells which enhanced the fill factor (FF) of p-DTS(FBTTh2)2/PC71BM BHJ solar cell up to 75.1%, one of the highest value reported for an organic solar cell. The external quantum efficiency exceeds 80%. Analysis of recombination mechanisms using the current-voltage (J–V) characteristics at various light intensities in the BHJ solar cell layer reveals that Ba prevents trap assisted Shockley-Read-Hall (SRH) recombination at the interface and with different thicknesses of the Ba, the recombination shifts towards bimolecular from monomolecular. Moreover, Ba increases shunt resistance and decreases the series resistance significantly. This results in an increase in the charge collection probability leading to high FF. This work identifies a new cathode interlayer which outclasses the all the reported interlayers in increasing FF leading to high power conversion efficiency and have significant implications in improving the performance of BHJ solar cells.

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“…[3][4][5][6][7][8][9] Among them, the most popular one is BCP, since it can greatly improve the power conversion efficiency (PCE) as compared to others. 10,11 Fig. 1 shows the chemical structure of BCP molecule.…”

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confidence: 99%

Favorable electronic structure for organic solar cells induced by strong interaction at interface

Wang

Sakurai

Hao

et al. 2013

Journal of Applied Physics

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Effects of cathode buffer layers on the efficiency of bulk-heterojunction solar cells

Cited by 59 publications

References 27 publications

How the Charge-Neutrality Level of Interface States Controls Energy Level Alignment in Cathode Contacts of Organic Bulk-Heterojunction Solar Cells

How the Charge-Neutrality Level of Interface States Controls Energy Level Alignment in Cathode Contacts of Organic Bulk-Heterojunction Solar Cells

Barium: An Efficient Cathode Layer for Bulk-heterojunction Solar Cells

Favorable electronic structure for organic solar cells induced by strong interaction at interface

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