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Title: Effects of humidity during formation of zinc oxide electron contact layers from a diethylzinc precursor solution

Here, this work focuses on the role of humidity in the formation of ZnO thin films from a reactive diethylzinc precursor solution for use as the electron contact layer (ECL) in organic photovoltaic (OPV) devices. This method is well suited for flexible devices because the films are annealed at 120 °C, making the process compatible with polymer substrates. ZnO films were prepared by spin coating and annealing at different relative humidity (RH) levels. It is found that RH during coating and annealing affects the chemical and physical properties of the ZnO films. Using x-ray photoelectron spectroscopy it is found that increasing RH during the formation steps produces a more stoichiometric oxide and a higher Zn/O ratio. Spectroscopic ellipsometry data shows a small decrease in the optical band gap with increased humidity, consistent with a more stoichiometric oxide. Kelvin probe measurements show that increased RH during formation results in a larger work function (i.e. further from vacuum). Consistent with these data, but counter to what might be expected, when these ZnO films are used as ECLs in OPV devices those with ZnO ECLs processed in low RH (less stoichiometric) had higher power conversion efficiency than those with high-RH processed ZnO duemore » to improved open-circuit voltage. The increase in open-circuit voltage with decreasing humidity was observed with two different donor polymers and fullerene acceptors, which shows the trend is due to changes in ZnO. The observed changes in open-circuit voltage follow the same trend as the ZnO work function indicating that the increase in open-circuit voltage with decreasing humidity is the result of improved energetics at the interface between the bulk-heterojunction and the ZnO layer due to a vacuum level shift.« less
 [1] ;  [1] ;  [2] ;  [3] ;  [1] ;  [4]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Colorado, Boulder, CO (United States); Friedrich-Alexander Univ., Erlangen (Germany)
  3. Friedrich-Alexander Univ., Erlangen (Germany)
  4. SolarWindow Technologies, Inc., Columbia, MD (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1566-1199
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Organic Electronics
Additional Journal Information:
Journal Volume: 31; Related Information: Organic Electronics; Journal ID: ISSN 1566-1199
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE NREL-Solar Window Technologies, Inc. Cooperative Research and Development Agreement (CRADA); USDOE
Country of Publication:
United States
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; organic photovoltaics; zinc oxide; processing; humidity; contact layer
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1341200