title: Surface Passivation for Reliable Measurement of Bulk Electronic Properties of Heterojunction Devices.
abstract: Quantum efficiency measurements of state of the art Cu(In,Ga)Se2(CIGS) thin film solar cells reveal current losses in the near infrared spectral region. These losses can be ascribed to inadequate optical absorption or poor collection of photogenerated charge carriers. Insight on the limiting mechanism is crucial for the development of more efficient devices. The electron beam induced current measurement technique applied on device cross-sections promises an experimental access to depth resolved information about the charge carrier collection probability. Here, this technique is used to show that charge carrier collection in CIGS deposited by multistage co-evaporation at low temperature is efficient over the optically active region and collection losses are minor as compared to the optical ones. Implications on the favorable absorber design are discussed. Furthermore, it is observed that the measurement is strongly affected by cross-section surface recombination and an accurate determination of the collection efficiency is not possible. Therefore it is proposed and shown that the use of an Al2O3layer deposited onto the cleaved cross-section significantly improves the accuracy of the measurement by reducing the surface recombination. A model for the passivation mechanism is presented and the passivation concept is extended to other solar cell technologies such as CdTe and Cu2(Zn,Sn)(S,Se)4.
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bissig
authors.affiliation: Laboratory for Mechanics of Materials and Nanostructures, Empa-Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkerstrasse 39, 3602, Thun, Switzerland.
authors.forename: Carlos
authors.initials: C
authors.lastname: Guerra-Nunez
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Romain
authors.initials: R
authors.lastname: Carron
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Shiro
authors.initials: S
authors.lastname: Nishiwaki
authors.affiliation: Reliability Science and Technology Laboratory, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Fabio
authors.initials: F
authors.lastname: La Mattina
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Fabian
authors.initials: F
authors.lastname: Pianezzi
authors.affiliation: Zurich University of Applied Sciences (ZHAW), School of Engineering, Institute of Computational Physics, Technikumstrasse 9, 8401, Winterthur, Switzerland.
authors.forename: Paolo A
authors.initials: PA
authors.lastname: Losio
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Enrico
authors.initials: E
authors.lastname: Avancini
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Reinhard
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Stefan G
authors.initials: SG
authors.lastname: Haass
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Martina
authors.initials: M
authors.lastname: Lingg
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Feurer
authors.affiliation: Laboratory for Mechanics of Materials and Nanostructures, Empa-Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkerstrasse 39, 3602, Thun, Switzerland.
authors.forename: Ivo
authors.initials: I
authors.lastname: Utke
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland. stephan.buecheler@empa.ch.
authors.forename: Stephan
authors.initials: S
authors.lastname: Buecheler
authors.affiliation: Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland.
authors.forename: Ayodhya N
authors.initials: AN
authors.lastname: Tiwari
keywords: CIGS; atomic layer deposition; electron beam induced current; heterojunctions; surface passivation; thin film solar cells