Solar cells based on Cu(In_1-xGa_x)Se₂ (CIGS) thin film absorbers show very high efficiencies and performance stabilities. Empa has developed a scalable deposition process for CIGS thin-film solar cells suitable for high-speed and in-line production on flexible polymer foils. The thickness of the completed solar cell including the polymer substrate is less than 25 µm.

A world record efficiency of 20.8% was recently achieved.

Main research topics include:

• engineering of band gap, composition and interfaces of the CIGS absorber for optimum device efficiency and upscaling potential,
• investigation of the solar cell electrical, optical properties as well as performance loss mechanisms,
• advances with alternative environmental-friendly processes for other constituent layers,
• development of low-bandgap absorbers for high-performance multijunction (tandem) solar cells

The development of highly efficient, stable, light weight and flexible solar cells is important for emerging markets such as building-integrated (BIPV), portable electronics, mobility as well as for aerospace applications. A spin-off of the group scales-up and commercializes solar modules based on the technology developed in the lab.

• Carron, R., Nishiwaki, S., Feurer, T., Hertwig, R., Avancini, E., Löckinger, J., Yang, Sh., Buecheler, S., Tiwari, A. N. (2019). Advanced alkali treatments for high‐efficiency Cu(In,Ga)Se₂ solar cells on flexible substrates. Advanced Energy Materials, 9 (24), 1900408 (8 pp.).
• Feurer, T., Carron, R., Torres Sevilla, G., Fu, F., Pisoni, S., Romanyuk, Y. E., Buecheler, S., Tiwari, A. N. (2019). Efficiency improvement of near‐stoichiometric CuInSe₂Solar cells for application in tandem devices. Advanced Energy Materials, 9 (35), 1901428 (6 pp.).
• Weiss, T. P., Bissig, B., Feurer, T., Carron, R., Buecheler, S., & Tiwari, A. N. (2019). Bulk and surface recombination properties in thin film semiconductors with different surface treatments from time-resolved photoluminescence measurements. Scientific Reports, 9 (1), 5385 (13 pp.).

   

   

   

   

Kesterite is a thin-film solar cell technology. Its constituent metals (Cu, Sn, Zn, S and Se, in short CZTSSe) are abundant in the earth crust, thus it is a sustainable alternative to e.g. CIGS for the substitution of critical raw materials (CRM) like In and Ga. This also offers a secure supply chain as the metal production is distributed worldwide. Kesterite technology is also fully compatible with current CIGS production lines, thus it has a realistic potential to achieve the efficiency levels required for transferring the processes to relevant industrial environments.

Empa reached efficiencies up to 12.2% (active area) through lithium addition via a non-vacuum precursor synthesis route, close to the 12.6% world record. The main factor limiting the performance is explained by the large V_oc-deficit.

Main research activities are:

• investigation on defect passivation via chemical treatments;
• engineering  of absorber annealing and composition;
• analysis of defect type and concentration.

• A. Cabas-Vidani, S. G. Haass, C. Andres, R. Caballero, R. Figi, C. Schreiner, J. A. Márquez, C. Hages, T. Unold, D. Bleiner, A. N. Tiwari, Y. E. Romanyuk, Adv. Energy Mater. 2018, DOI 10.1002/aenm.201801191.