关于举行芬兰Åbo Akademi大学Ronald Mattias Österbacka教授学术报告的通知

报告人：芬兰Åbo Akademi大学Ronald Mattias Österbacka教授

报告题目： New regimes for extraction current transients in thin-film solar cells

时间：2017年10月26日上午10：00-11：30

地点: 国重大楼501 室

报告摘要:

Processes taking place at contacts are of particular importance in organic and perovskite solar cells where selective contacts that are able to efficiently collect majority carriers, simultaneously blocking minority carriers, are desired. The surface recombination velocity , describing the quality of the contact interface, is a key parameter in obtaining an increased understanding of the kinetics taking place at contacts in thin-film devices. In devices where the effective carrier transport velocity in the bulk is smaller than the surface recombination velocity , the surface recombination at the contact is limited by diffusion in the bulk. However, in the case when , the charge transport is limited by kinetics at the contact rather than by the transport in the bulk.

We have extended the analytical framework of the charge extraction by linearly increasing voltage (CELIV) theory taking the effect of built-in voltage, diffusion and band-bending into account [1]. We have used the new CELIV-regime as an in-device characterization technique to clarify the origin of the light-soaking issue in inverted solar cells employing titanium dioxide (TiO₂) as an electron selective layer. We have derived analytical expressions describing the effective reduction of the built-in voltage and the (effective) open-circuit voltage providing means to quantify and distinguish various mechanisms for contact related effects in solar cells [2]. An injected hole reservoir accumulated at the TiO₂/organic interface of the pristine device is observed from the extraction current transients; the hole reservoir screens the internal electric field causing an S-shape in the JV curve of pristine devices. Furthermore, we can show that the work function (WF) of the ITO/TiO₂-contact decreases upon UV exposure. This results in an increased built-in voltage which hinders the build-up of a hole reservoir, thus removing the S-shape [3].

The method is also used to determine surface recombination velocities at selective and/or blocking contacts in thin-film devices. allowing us to directly estimating the dynamics at selective contacts [4].

References

[1] O. Sandberg, M. Nyman, R. Österbacka, Organic Electronics 15, 3413-3420 (2015)

[2] O. Sandberg, M. Nyman, R. Österbacka, Physical Review Applied 1, 024003 (2014)

[3] A. Sundqvist, M. Nyman, O. Sandberg, S. Sandén, J.-H. Smått, and R. Österbacka, Advanced Energy Materials, 1502265 (2016)

[4] O.J. Sandberg, et. al, Physical Review Letters, 118, 076601 (2017).

附: Österbacka教授简历

Prof. Österbacka has published more than 180 papers in major international journals since 1996, with a total of 5009 citations (without self-citations, 19.09.2017), yielding an h-index of 37. The publications include one in Science, four in Physical Review Letters, four in Advanced Materials, 10 in Organic Electronics, 20 in Physical Review, and 12 in Applied Physics Letters. In addition he has three granted patents and several patent applications and has been invited more than 50 times to give invited lectures at international conferences and summer schools since 2006.