Conferences and exhibitions

The EU PVSEC is the largest international conference for photovoltaics in the areas of research, technologies and applications with an accompanying industrial exhibition, in which representatives of the photovoltaic industry present their technologies, innovations and new concepts.  This year the EU PVSEC will again be held online. Dr. Volker Sittinger, head of the Department Diamond-based Systems and Applications at the Fraunhofer IST, and Hunter King are participating in the conference with a presentation and a poster.

Monday, September 6, 2021 (Session 3AO.4), 2:00 pm

»Tacking the challenges for industrialization of perovskite silicon tandem solar cells«

J.C. Goldschmidt, P.S.C. Schulze, O.S. Kabakli, A.J. Bett, M. Bivour, R. Efinger, F. Feldmann, F.M. Gerspacher, B.S. Goraya, M. Heydarian, C. Luderer, C. Messmer, H. Nagel, S. NOld, M. Penn, C. Reichel, M.C. Schubert, C.A. Romero Sierra, L. Tutsch, M. Hermle, S.W. Glunz (Fraunhofer ISE); B. Fett, B. Herbig (Fraunhofer ISC),  H. King, V. Sittinger (Fraunhofer IST), S. Lange, V. Nauann (Fraunhofer CSP)

Dienstag, 7. September 2021 (Session 3BV.2), 10:30 - 12:00 am

»Optimizing Top-TCO for perovskite-silicon tandem solar cells«

H. King, V. Sittinger, T. Harig (Fraunhofer IST), O.S. Kabakli, P.S.C. Schulze, J.C. Goldschmidt (Fraunhofer ISE)

1.     MOTIVATION

Using sputtering processes Indium Tin Oxide and Indium Zinc Oxide films were developed for use in Perovskite-Silicon tandem solar cells as a TCO top-layer. Perovskite absorber materials have shown significant promise in the last 10 years for use alone or in tandem cell configurations. However, due to increased temperature instability when compared with their silicon counterparts, new processes and materials must be developed for the surrounding contact layers in order to maximize both cell performance and lifetime. For this purpose, ITO and IZO films with the temperature limitations of the perovskite absorber in mind (Tmax < 100 °C). The optimum process parameters are determined by optical and conductivity measurements, in addition to contact resistivity measurements between the TCO layer and the neighboring buffer layers.

2.     EXPERIMENTAL DETAILS

ITO films were produced using a DC sputter process utilizing a 95/5 [In/Sn wt. %] ceramic target, while the IZO films were produced by means of a reactive co-sputtering process. In the case of the IZO the Zinc concentration was varied by means of a variation in sputter power in the planar cathode towards the Indium rotatable target. Film stoichiometries were confirmed by means of EPMA measurements, optical measurements consisted of photometry and ellipsometric measurements, and electrical measurements consisted of 4-point conductivity and Hall effect measurements in order to confirm the carrier concentration and mobility of the films.

3.     RESULTS AND OUTLOOK

TCO films were optimized for perovskite-silicon tandem cell applications. The ITO films were optimized as a function of additional mixed gas [Argon/Oxygen 90/10 %] and additional hydrogen gas. An optimum between film absorption and conductivity was found, while maintaining deposition temperatures below 100 °C. The IZO films were optimized as a function of additional oxygen flow rate by maintaining operation in the sputtering transition zone between metallic and oxide operation. In this range the films were optimized to minimize film absorption and maximize conductivity. 

These optimized TCO films will be implemented into newly developed perovskite-silicon tandem solar cells which utilize new state of the art material combinations, as produced from partner institutes within the Fraunhofer Society.

ACKNOWLEDGEMENT

This work was supported as a Fraunhofer LIGHTHOUSE PROJECT.