Suchergebnisse

Room temperature pseudodielectric function spectra ε(ω) ≤ ε1 (ω) + iε2(ω) of the ordered defects compounds Cu2In4Se7, CuGa 3Se5 and CuGa5Se8 have been measured by spectroscopic ellipsometry. The values of refractive index n and extinction coefficient k are given. The structures observed in ε(ω) spectra have been analysed using different methods, including fitting the numerically differentiated experimental spectrum (second derivative) to analytical line shapes. As a result, the energies corresponding to the fundamental gap (E 0) and higher critical points have been determined. A linear correlation of the fundamental gap values with Ga/Cu atomic ratio contents in CuGaxSey samples is deduced. © 2007 IOP Publishing Ltd. ; Financial support from the INTAS Program (Project 03-51-6314) Comunidad de Madrid (Project FOTOFLEX S-0505/ENE/0123) and from the Spanish Government MEC projects ENE 2004-07446-C02-01/ALT/ and MAT2003- 01490 is acknowledged. ; Peer Reviewed

The cation disorder in Cu2ZnSnS4 thin films grown by flash evaporation of ZnS, CuS and SnS binary compounds has been studied by Raman spectroscopy. Process parameters such as the substrate temperature during the evaporation and the Ar pressure in the post-thermal treatment determined the samples' composition and Raman spectra. As a measure of cation disorder, the half-width and relative intensity of the Raman band peaking at 331-332 cm-1 is analysed. Comparison of the spectra for different samples of known composition showed that the relative intensity of the 331 cm-1 defect peak correlates with the previously reported theoretical prediction about enhancement of antisite defect formation in Cu2ZnSnS4 under "Cu-poor, Zn-rich" conditions. For "Cu-rich, Zn-poor" films, further experimental confirmation was obtained of the previously detected effect of the enhancement of cation disorder under intense optical excitation ; This research is supported by the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Program FP7/2007-2013/ under REA grant greement 269167 (PVICOKEST), the Spanish MINECO project (KEST- PV, ENE2010-21541-C03) and the OPTEC grant. RC acknowledges financial support from Spanish MINECO within the program Ramon y Cajal (RYC-2011-08521)

Cu2ZnSnS4 thin films have been produced via rapid thermal evaporation of off-stoichiometric kesterite powder followed by annealing in an Ar atmosphere. Different heating rates were applied during the thermal treatments. The chemical composition and structural properties of the deposited layers as well as the distribution of the elements through the kesterite thin film have been investigated. The initial growth of a SnS secondary phase during evaporation led to the formation of this secondary phase next to the Mo back contact. Solar cell power conversion efficiencies were limited to values about 3 % due to this secondary phase. Furthermore, an increased open circuit voltage was demonstrated by using a Zn(O,S) buffer layer ; This work was supported by DAAD project (INTERKEST, Ref: 57050358), Marie Curie-ITN (KESTCELLS, GA: 316488) and MINECO project (SUNBEAM, ENE2013-49136-C4-3-R). RC and ES acknowledge financial support from Spanish MINECO within the Ramón y Cajal program (RYC-2011-08521) and (RYC-2011-09212) respectively. SG also thanks the Government of Spain for the FPI fellowship (BES-2014-068533).