Efficient Solution‐Processed Small‐Molecule Solar Cells with Inverted Structure

Kyaw, Aung Ko Ko; Wang, Dong Hwan; Gupta, Vinay; Zhang, Jie; Chand, Suresh; Bazan, Guillermo C.; Heeger, Alan J.

doi:10.1002/adma.201300295

Cited by 488 publications

(429 citation statements)

References 43 publications

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“…Compared to devices with ZnO, a less decay in PCE was observed for the ZnO/PEI CIL‐based devices without encapsulation, further demonstrating the improved stability with this hybrid CIL. Similar results were also documented in solution‐processed PEIE‐modified ZnO CILs, by which inverted small‐molecule OSCs with enhanced PCEs up to 7.88% were achieved 178. This hybrid CIL‐based inverted OSCs were relatively stable in air compared to the conventional devices, demonstrating a promising way to the fabrication of small‐molecule OSCs with high efficiency and long‐term stability.…”

Section: Electron‐transporting Materials As Cilssupporting

confidence: 79%

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

2016

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Organic solar cells (OSCs) have shown great promise as low‐cost photovoltaic devices for solar energy conversion over the past decade. Interfacial engineering provides a powerful strategy to enhance efficiency and stability of OSCs. With the rapid advances of interface layer materials and active layer materials, power conversion efficiencies (PCEs) of both single‐junction and tandem OSCs have exceeded a landmark value of 10%. This review summarizes the latest advances in interfacial layers for single‐junction and tandem OSCs. Electron or hole transporting materials, including metal oxides, polymers/small‐molecules, metals and metal salts/complexes, carbon‐based materials, organic‐inorganic hybrids/composites, and other emerging materials, are systemically presented as cathode and anode interface layers for high performance OSCs. Meanwhile, incorporating these electron‐transporting and hole‐transporting layer materials as building blocks, a variety of interconnecting layers for conventional or inverted tandem OSCs are comprehensively discussed, along with their functions to bridge the difference between adjacent subcells. By analyzing the structure–property relationships of various interfacial materials, the important design rules for such materials towards high efficiency and stable OSCs are highlighted. Finally, we present a brief summary as well as some perspectives to help researchers understand the current challenges and opportunities in this emerging area of research.

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Section: Electron‐transporting Materials As Cilssupporting

confidence: 79%

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

2016

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“…A new generation of WMLs fi rst introduced by Cao et al is based on polyelectrolytes or tertiary aliphatic amines, such as poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt -2,7-(9,9-dioctylfluorene)] (PFN) and the corresponding ethyl ammonium bromide. [ 1 ] Although these materials improve carrier injection or extraction in different organic diode devices, [1][2][3][4][5][6][7] the mechanism behind this improvement is not completely clear. This ambiguity hinders design, selection and optimization of new WMLs.…”

mentioning

confidence: 99%

Origin of Work Function Modification by Ionic and Amine‐Based Interface Layers

Reenen

Kouijzer

Janssen

et al. 2014

Adv Materials Inter

131

138

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can evolve into a successful thin fi lm photovoltaic technology. To this end, further improvements in the sunlight-toelectricity conversion effi ciency are still needed. To do so, not only the optoelectronic, active layer should be considered, but also the connection between this layer and the electrodes. This connection is facilitated by so-called work function modifi cation layers (WMLs) that serve to align the transport levels in the organic semiconductor and the conductor by modifi cation of the work function. Materials that are often used are poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) for improving hole collection and injection in combination with an indium tin oxide (ITO) electrode and LiF for the electron contact in combination with an Al metal electrode. A new generation of WMLs fi rst introduced by Cao et al. is based on polyelectrolytes or tertiary aliphatic amines, such as poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt -2,7-(9,9-dioctylfluorene)] (PFN) and the corresponding ethyl ammonium bromide. [ 1 ] Although these materials improve carrier injection or extraction in different organic diode devices, [1][2][3][4][5][6][7] the mechanism behind this improvement is not completely clear. This ambiguity hinders design, selection and optimization of new WMLs.Mechanisms that are generally considered to result in electric fi elds and concomitant work function shifts at metal-organic interfaces are doping, charge transfer, and dipole formation. [8][9][10] Regarding the work function modifi cation of amine side-groups, Lindell et al. [ 11 ] found by photoelectron spectroscopy and density functional calculations that the electron donor para-phenylenediamine chemisorbs onto atomically clean Ni in vacuum. [ 12 ] Due to partial electron transfer from the amine unit, a work function reduction of 1.55 eV is achieved, resulting in a less deep Fermi level. This explanation is not likely to hold for the technologically more relevant procedure on which we shall focus, being the deposition of WMLs from solution on a metal at atmospheric pressure: the metal is not atomically clean, which likely inhibits chemisorption. In other work by Zhou et al. [ 13 ] it is shown that the work function reduction, at atmospheric pressure, by the amine groups in poly(ethylenimine ethoxylated) (PEIE), is generally the same on different conductors. Work function modifi cation by polyelectrolytes and tertiary aliphatic amines is found to be due to the formation of a net dipole at the electrode interface, induced by interaction with its own image dipole in the electrode. In polyelectrolytes differences in size and side groups between the moving ions lead to differences in approach distance towards the surface. These differences determine magnitude and direction of the resulting dipole. In tertiary aliphatic amines the lone pairs of electrons are anticipated to shift towards their image when close to the interface rather than the nitrogen nuclei, which are sterically hindered by the alkyl side chains. ...

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“…The advantages of small molecule donors include relatively simple synthesis and purification, well-defined structures, no end group contaminants, high charge carrier mobility and less batch-to-batch variation [16,17]. To date, the PCEs of solar cells using small molecules as donors have exceeded 8% [18,19], and this makes these materials ideal candidates for solution-processed OSCs.…”

Section: Introductionmentioning

confidence: 99%

“…Bazan and Heeger have reported 6.7% PCEs normal SM-OSCs devices [20], 7.88% PCEs inverted structure SM-OSCs devices [18] and 8.9% PCEs ZnO optical spaced SM-OSCs devices [21] based on p-DTS(FBTTh 2 ) 2 (Fig. 1), one thiophene and benzothiadiazole end-capped dithiophenesilolo (DTS) molecule.…”

Section: Introductionmentioning

confidence: 99%

Benzo[1,2-b:4,5-b′]dithiophene and benzotriazole based small molecule for solution-processed organic solar cells

Chen

et al. 2014

Organic Electronics

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Efficient Solution‐Processed Small‐Molecule Solar Cells with Inverted Structure

Cited by 488 publications

References 43 publications

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

Origin of Work Function Modification by Ionic and Amine‐Based Interface Layers

Benzo[1,2-b:4,5-b′]dithiophene and benzotriazole based small molecule for solution-processed organic solar cells

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