WP4 - Thin film solar cell production
This WP is expected to provide CdTe/CdS and CuInGaSe2/CdS thin film solar cells both on rigid and flexible substrates. In order to have electrical “series” interconnections between the various cells constituting the photovoltaic module, standard P1, P2, P3 laser scribings will be made on these devices. The three steps are the patterning of the back contact (P1), the removal of the active layer (P2) and the isolation cut (P3).
The photovoltaic devices in "substrate" configuration (CdTe/CdS and CuInGaSe2/CdS) will be carried out both on flexible polymeric and metallic substrates. In this case, a new type of laser scribing, having different solar cell configurations and substrates, has to be developed. All devices will be provided to partners who will develop the laser scribing. The WP4 partners are:
Solar system and Equipment (SSE) (http://www.solar-sse.com) will provide samples of CdTe on glass substrates and CIGS on both glass substrates and metallic flexible substrates to partners for testing the scribing with the new fiber lasers. CdTe samples will be prepared with the novel process developed at the Department of Physics of Parma University which is being used in the new photovoltaic plant being installed by Arendi s.r.l. Samples for P1, P2, P3 and for edge cleaning will be provided. SSE will also provide CIGS samples to the partners prepared with new precursors deposited by sputtering on glass, Mo or stainless steel foils. The new precursors consist in stacks of In2Se3, Ga2Se3, Cu and CuGa all deposited by sputtering one on top of each other and annealed at high temperature. The mixed material is then selenized at high temperature in a selenium atmosphere in order to form the desired CuInGaSe2 compound.
Würth Solar (WS) (www.wuerth-solar.de) will deliver CIS modules (glass substrates, 60 x 120 cm2) that can be taken from running production before and after any relevant processing appropriate for laser applications (P1-P3, edge cleaning) in WP5. The modules are produced in high quality with a good reproducibility and efficiencies of ca. 12%. For this reason a reliable basis for testing of laser processes is given. All modules will be examined carefully before delivery. After finishing laser application tests, selected and accurately examined modules will be completed in the production line in order to compare them with standard modules.
Zentrum für Sonnenenergie und Wasserstoff-Forschung (ZSW) (http://www.zsw-bw.de/index.php?id=9&L=1) provides CIS on rigid and on flexible substrates. CIS on glass substrates can be used as a kind of standard for high performance thin-film modules. It can be produced with high reproducibility and has the further advantage of being easy to handle. Therefore it provides a good basis for fundamental testing of the laser processes. ZSW will also provide CIS modules on both the two basically different flexible substrate types, electrically conductive and insulating materials. The conductive material will be stainless steel, which has to be covered by an insulating barrier. At ZSW silicon oxide is used as a barrier material.
Nexcis Photovoltaic Technology will provide electrodeposited based CIS on glass and on flexible substrates for the testing of new fiber lasers. CIS on glass substrates can be used as standard. They can be produced with high reproducibility and have the further advantage of being easy to handle. Nexcis will also provide CIS modules on metallic substrates with both characteristics, electrically conductive and insulating materials. The conductive material will be stainless steel, which has to be covered by an insulating barrier. Other kind of metallic substrates will be proposed to partner during the project. Silicon oxide will be the barrier material. Substrates covered with a barrier, a Mo contact layer and CISEL structure up to i-ZnO will be supplied to the laser scribing partners.
University of Verona (UNIVR) (http://profs.sci.univr.it/~romeo/) The objectives are to improve the fabrication process with a suitable polymer and to optimize the process in order to get high efficiency and stable flexible CdTe based devices. The substrate configuration devices will also be taken into account in order not to be limited by transparency requirement. In this way, different materials could be used as substrates like molybdenum plates which reduce the process temperature limitations. Moreover the modified polymers will then be used for the fabrication of the devices and a study of the structure of the crystalline deposited layers will be done. We plan to first use commercial polymers like Upilex and Kapton, studying their resistance at high temperatures in connection with thickness, the deposition parameters and transparency under different treatment conditions. Solar cells samples made on different substrates will be supplied to the laser scribing partners.