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

Journal Article · · Organic Electronics
 [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)
+ Show Author Affiliations

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 due 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.

Research Organization:
National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE NREL-Solar Window Technologies, Inc. Cooperative Research and Development Agreement (CRADA); USDOE
Grant/Contract Number:
AC36-08GO28308
OSTI ID:
1237035
Alternate ID(s):
OSTI ID: 1341200
Report Number(s):
NREL/JA-5900-64538
Journal Information:
Organic Electronics, Vol. 31; Related Information: Organic Electronics; ISSN 1566-1199
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 3 works
Citation information provided by
Web of Science

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Related Subjects

14 SOLAR ENERGY
36 MATERIALS SCIENCE
organic photovoltaics
zinc oxide
processing
humidity
contact layer