LACTEL: Large area cadmium telluride electrodeposition for thin film solar cells

• Forschungsstelle: EU FRP
• Projektnummer: 96.0256
• Projekttitel Englisch: LACTEL: Large area cadmium telluride electrodeposition for thin film solar cells

Schlüsselwörter (Englisch)

CdTe; solar cells; solar energy; thin films; photovoltaics; vacuum evaporation

Alternative Projektnummern (Englisch)

EU project number: JOR3-CT97-0150

Forschungsprogramme (Englisch)

EU-programme: 4. Frame Research Programme - 5.1 Nonnuclear energies

Kurzbeschreibung (Englisch)

See abstract

Partner und Internationale Organisationen (Englisch)

BP Solar (UK), Philips (NL), ENSCP (F) JRC-ISPRA (I), FISE (D), INM(D), ETHZ (CH)

Abstract (Englisch)

Industrial production of large area CdTe/CdS modules requires the growth of uniform CdTe layers with very high deposition rates. For a 'specific application' deposition of acid and heat resistant metal grids on FTO/glass was required by industrial partners. The contribution of the IQE-ETHZ was focussed on three topics: (i) characterization and optimization of screen printed metal lines and their thermal and chemical stability; (ii) characteriaztion of the CdS and CdTe layers, particularly the recrystallization and intermixing; (iii) Development and characterization of solar cells on different substrates, including the inverted structure.

Metal lines (grids) were screen printed using a variety of metallic pastes (collaboration with GVE-EMPA). Sintering conditions were optimized to obtain low resistance and well defined lines of Ag (with pastes from Dupont, ESL and INM developed IPS45) and Ni (paste supplied by Philips). Importance of an optimum sintering (coalescence of the grains/particles) was proven by comparing the microstructure of the lines, measured with scanning electron microscopy, with the electrical resistance. The chemical and thermal stability of lines printed with different pastes were measured by analysing the CdS and CdTe bath solutions with the atomic absorption spectrometry (AAS). Single and bilayer (meatl covered with a protective layer) grids were analysed. Leaching of metal in the CdTe bath is substantially reduced when a protective coating is applied.

Investigations were performed to understand the recrystallization and intermixing in CdTe/CdS processed under different conditions. The grain size of electrodeposited CdTe increases when the layers are annealed at about 400 °C. The CdCl2 treated (and annealed) CdTe layers have larger grains but the cell efficiency is low due to excessive intermixing at the interface of CdTe-CdS. This is in contrast to the results observed for solar cells made with physical vapor deposition (PVD) methods. The microstructure of PVD grown CdTe layers, annealing induced recrystallization and intermixing, and solar cell efficiency depend on the CdS deposition method and transparent conducting oxides.

Different type of TCOs such as ZnO, ITO and SnOx:F were used for the growth of 'superstrate' solar cells. For the development of inverted solar cells in 'substrate configuration' preliminary experiments were performed. Vacuum evaporated Mo and Sb2Te3/Mo layers were used as a back contact for CdTe. The grain size and crystal orientation of CdTe depend on the back contact buffer layer and post-deposition annealing treatment. The efficiency of inverted solar cells was low despite of the large grain size of CdTe; intermixing and front contact deposition needs optimization to increase the efficiency. Solar cells on SnOx: F and ITO with conversion efficiency of more than 12% were developed with a PVD method.

Datenbankreferenzen (Englisch)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 96.0256