Steffen Duhm

Name:

Organization: Soochow University

Department: Institute of Functional Nano & Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices

Title:

Chemicals
References

Improved Performance and Stability of All-Inorganic Perovskite Light-Emitting Diodes by Antisolvent Vapor Treatment

Co-reporter:Chen Wu;Yatao Zou;Tian Wu;Muyang Ban;Vincenzo Pecunia;Yujie Han;Qipeng Liu;Tao Song;Baoquan Sun

Advanced Functional Materials 2017 Volume 27(Issue 28) pp:

Publication Date(Web):2017/07/01

DOI:10.1002/adfm.201700338

All-inorganic perovskite light-emitting diodes (LEDs) reveal efficient luminescence with high color purity, but their modest brightness and poor stability are still critical drawbacks. Here, the luminescent efficiency and the stability of perovskite LEDs (PeLEDs) are boosted by antisolvent vapor treatment of CsPbBr3 embedded in a dielectric polymer matrix of polyethylene oxide (PEO). A unique method is developed to obtain high quality CsPbBr3 emitting layers with low defects by controlling their grain sizes. CsPbBr3 in PEO matrix is post-treated with antisolvent of chloroform (CF), leading to microcrystals with a size of ≈5 µm along the in-plane direction with active emitting composite of 90%. A device based on CF post-treatment (CsPbBr3-PEO-CF) film displays a brightness of up to 51890 cd m−2 with an external quantum efficiency of 4.76%. CsPbBr3-PEO-CF PeLED still maintains 82% of its initial efficiency after 80 h continuous operation in ambient air, which indicates relatively good device stability. This work highlights that film quality is not only key to promoting fluorescence in CsPbBr3, but also to achieving higher performance PeLEDs.

Transient Monolayer Structure of Rubrene on Graphite: Impact on Hole–Phonon Coupling

Co-reporter:Yang He

The Journal of Physical Chemistry C 2016 Volume 120(Issue 27) pp:14568-14574

Publication Date(Web):June 20, 2016

DOI:10.1021/acs.jpcc.6b04848

Charge transport in molecular thin films is often dominated by incoherent hopping processes, and charge-carrier phonon coupling plays a major role in defining mobilities. Our high resolution angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) study reveals the influence of molecular configuration and packing on the hole-phonon coupling in vacuum-sublimed thin films of rubrene on graphite and allows determining charge reorganization energies. In the contact layer to the substrate rubrene is well-ordered with, for low coverages, the tetracene backbone being almost parallel to the graphite surface forming a loose-packed monolayer. Increasing the coverage leads to an orientational transition and a more tilted orientation of rubrene in a close-packed monolayer. This transition results in dramatic changes of spectral features in ARUPS including the photoelectron angular distribution of the highest occupied molecular orbital derived intensity. The charge reorganization energy, however, only changes slightly. The transient monolayer structure of rubrene on graphite allows us, thus, to demonstrate that hole-phonon coupling in organic thin films does not depend very critically on the packing structure.

HATCN-based Charge Recombination Layers as Effective Interconnectors for Tandem Organic Solar Cells

Co-reporter:Rong-Bin Wang, Qian-Kun Wang, Hao-Jun Xie, Lu-Hai Xu, Steffen Duhm, Yan-Qing Li, and Jian-Xin Tang

ACS Applied Materials & Interfaces 2014 Volume 6(Issue 17) pp:15604

Publication Date(Web):August 20, 2014

DOI:10.1021/am504620x

A comprehensive understanding of the energy-level alignment at the organic heterojunction interfaces is of paramount importance to optimize the performance of organic solar cells (OSCs). Here, the detailed electronic structures of organic interconnectors, consisting of cesium fluoride-doped 4,7-diphenyl-1,10-phenanthroline and hexaazatriphenylene–hexacarbonitrile (HATCN), have been investigated via in situ photoemission spectroscopy, and their impact on the charge recombination process in tandem OSCs has been identified. The experimental determination shows that the HATCN interlayer plays a significant role in the interface energetics with a dramatic decrease in the reverse built-in potential for electrons and holes from stacked subcells, which is beneficial to the charge recombination between HATCN and the adjacent layer. In accordance with the energy-level alignments, the open-circuit voltage of tandem OSC incorporating a HATCN-based interconnector is almost 2 times that of a single-cell OSC, revealing the effectiveness of the HATCN-based interconnectors in tandem organic devices.Keywords: charge recombination layers; electronic structure; HATCN; interconnector; tandem organic solar cell

Molecular Structure-Dependent Charge Injection and Doping Efficiencies of Organic Semiconductors: Impact of Side Chain Substitution

Co-reporter:Jinpeng Yang;Yanqing Li;Jianxin Tang;Satoshi Kera;Nobuo Ueno

Advanced Materials Interfaces 2014 Volume 1( Issue 3) pp:

Publication Date(Web):

DOI:10.1002/admi.201300128

Due to the highly anisotropic nature of π -conjugated molecules, the molecular structure of organic semiconductors can significantly affect the device performance of organic optoelectronics. Here, the molecular structure dependence on charge injection and doping efficiencies is investigated by characterizing the typical hole transport material of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) and its derivatives N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-9,9-dimethyl-fluorene (DMFL-NPB) and N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-9,9-diphenyl-fluorene (DPFL-NPB)]. Using photoelectron spectroscopy data and density functional theory calculation, it is identified that the side chain substitution in NPB and its derivatives plays a crucial role in the intrinsic injection and transport properties, and doping efficiency. The inner twist of the two main benzene rings in NPB is changed from out-of-plane to in-plane due to the alkyl or phenyl side chains of DMFL-NPB or DPFL-NPB, which reduces the ionization energies and thus decreases the hole injection barriers at the indium tin oxide/organic interface. The doping efficiency in 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄-TCNQ) doped systems is also highly dependent on the degree of intermolecular orbital energy hybridization with respect to the side chain substitution. These findings show that the rational design of molecular structures with suitable side chains is crucial for achieving high-performance organic devices.

Pentacene on Ag(111): Correlation of Bonding Distance with Intermolecular Interaction and Order

Co-reporter:Steffen Duhm, Christoph Bürker, Jens Niederhausen, Ingo Salzmann, Takuya Hosokai, Julien Duvernay, Satoshi Kera, Frank Schreiber, Norbert Koch, Nobuo Ueno, and Alexander Gerlach

ACS Applied Materials & Interfaces 2013 Volume 5(Issue 19) pp:9377

Publication Date(Web):September 9, 2013

DOI:10.1021/am402778u

We report coverage and temperature dependent bonding distances of vacuum-sublimed pentacene (PEN) submonolayers on Ag(111) obtained by the X-ray standing wave technique. The average vertical bonding distance of 2.98 Å at room temperature for 0.50 monolayer (ML) coverage increases to 3.12 Å for 0.75 ML due to competing intermolecular and adsorbate–substrate interactions. In contrast, decreasing the temperature from 295 to 145 K does not impact the bonding distance despite the concomitant transition from a “liquidlike” to an ordered molecular arrangement. In combination with X-ray photoelectron spectroscopy results, we could identify “soft chemisorption” with a subtle balance of molecule–molecule and substrate–molecule interactions as being responsible for this special adsorption behavior. Thus our study sheds light not only on the interface between PEN and Ag(111), but also on fundamental adsorption processes of organic adsorbates on metals in the context of chemi- and physisorption.Keywords: bonding distance; intermolecular interaction; organic adsorbate; pentacene; soft chemisorption; X-ray standing waves;