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Overcoming Electrode‐Induced Losses in Organic Solar Cells by Tailoring a Quasi‐Ohmic Contact to Fullerenes via Solution‐Processed Alkali Hydroxide Layers
Author(s) -
Zhang Hong,
Shallcross R. Clayton,
Li Ning,
Stubhan Tobias,
Hou Yi,
Chen Wei,
Ameri Tayebeh,
Turbiez Mathieu,
Armstrong Neal R.,
Brabec Christoph J.
Publication year - 2016
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201502195
Subject(s) - materials science , hydroxide , ohmic contact , oxide , alkali metal , fullerene , work function , fermi level , electron acceptor , passivation , chemical engineering , electrode , inorganic chemistry , chemical physics , nanotechnology , layer (electronics) , electron , photochemistry , chemistry , organic chemistry , metallurgy , engineering , physics , quantum mechanics
It is shown that the performance of inverted organic solar cells can be significantly improved by facilitating the formation of a quasi‐ohmic contact via solution‐processed alkali hydroxide (AOH) interlayers on top of n ‐type metal oxide (aluminum zinc oxide, AZO, and zinc oxide, ZnO) layers. AOHs significantly reduce the work function of metal oxides, and are further proven to effectively passivate defect states in these metal oxides. The interfacial energetics of these electron collecting contacts with a prototypical electron acceptor (C 60 ) are investigated to reveal the presence of a large interface dipole and a new interface state between the Fermi energy and the C 60 highest occupied molecular orbital for AOH‐modified AZO contacts. These novel interfacial gap states are a result of ground‐state electron transfer from the metal hydroxide‐functionalized AZO contact to the adsorbed molecules, which are hypothesized to be electronically hybridized with the contact. These interface states tail all the way to the Fermi energy, providing for a highly n ‐doped (metal‐like) interfacial molecular layer. Furthermore, the strong “light‐soaking” effect is no longer observed in devices with a AOH interface.