title: Single Molecular Precursor Solution for CuIn(S,Se)2Thin Films Photovoltaic Cells: Structure and Device Characteristics.
abstract: A single molecular precursor solution is described for the deposition of CuIn(S,Se)2(CIS) film onto Mo-coated glass substrates by spin coating, followed by annealing in Se atmosphere. Characterization of the films by X-ray diffraction, Raman spectroscopy and scanning electron microscopy demonstrates the formation of a highly homogeneous and compact 1.1 μm thick CIS layer, with a MoSe2under-layer. Atomic force microscopy reveals the presence of spherical grains between 400 and 450 nm, featuring surface corrugation in the range of 30 nm. Film composition is found to be in close agreement with that of the precursor solution. Diffuse reflectance spectroscopy shows a direct band gap (Eg) of 1.36 eV. Intensity and temperature dependence photoluminescence spectra show characteristic features associated with a donor-acceptor pair recombination mechanism, featuring activation energy of 34 meV. Over 85 solar cell devices with the configuration Mo/CIS/CdS/i-ZnO/Al:ZnO/Ni-Al and an total area of 0.5 cm2were fabricated and tested. The champion cell shows a power efficiency of 3.4% with an open circuit voltage of 521 mV and short circuit current of 14 mA/cm2under AM 1.5 illumination and an external quantum efficiency above 60%. Overall variation in each of solar cell parameters remains below 10% of the average value, demonstrating the remarkable homogeneity of this solution processing method. To understand the limitation of devices, the dependence of the open-circuit voltage and impedance spectra upon temperature were analyzed. The data reveal that the CuIn(S,Se)2/CdS interface is the main recombination pathway with an activation energy of 0.79 eV as well as the presence of two "bulk" defect states with activation energies of 37 and 122 meV. We also estimated that the MoSe2under-layer generates back contact barrier of 195 meV.
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: Devendra
authors.initials: D
authors.lastname: Tiwari
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
authors.forename: Tristan
authors.initials: T
authors.lastname: Koehler
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
authors.forename: Xianzhong
authors.initials: X
authors.lastname: Lin
authors.affiliation: H.H. Wills Physics Laboratory, University of Bristol , Tyndall Avenue, Bristol BS8 1TL. United Kingdom.
authors.forename: Andrei
authors.identifier: http://orcid.org/0000-0001-5617-4227
authors.initials: A
authors.lastname: Sarua
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: Harniman
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
authors.forename: Lan
authors.initials: L
authors.lastname: Wang
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie , Hahn-Meitner-Platz 1, D-14109 Berlin, Germany.
authors.forename: Reiner
authors.initials: R
authors.lastname: Klenk
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: David J
authors.identifier: http://orcid.org/0000-0002-0376-5506
authors.initials: DJ
authors.lastname: Fermin
keywords: CuIn(S,Se)2; impedance spectroscopy; recombination losses; solar cells; solution processing; thin films