Defect State Investigations in Methylammonium Lead Iodide Using the MIS-TSC Method
Svetlana Sirotinskaya a, Karsten Rojeck a, Roland Schmechel a, Niels Benson a
a University of Duisburg-Essen, Faculty of Engineering, Institute of Technology for Nanostructures (NST), Germany, Bismarckstraße, 81, Duisburg, Germany
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Oral, Svetlana Sirotinskaya, presentation 009
Publication date: 25th November 2019

Organic-inorganic perovskites are one of the most promising material classes for photovoltaic applications, since the achieved efficiency increased during the last 10 years from 3.8% to over 24% [1,2].While most of the research groups are working on the device efficiency and stability enhancement, there is still a lack of understanding and experimental validation of the influence of trap states on the perovskite charge carrier transport and especially the recombination properties. Besides the radiative and Auger recombinations, which relate to intrinsic recombination processes, the trap-assisted Shockley-Reed-Hall (SRH) and interface recombination play a critical role for the efficiency of perovskite solar cells. Therefore, here we experimentally investigate the energetic distribution of perovskite bulk and metal interface states on the example of methylammonium lead iodide (MAPI) thin-films.

For this purpose we use the thermally stimulated current (TSC) method. To avoid the well-known disadvantages of classical TSC, such as the recombination of complementary charge carriers and high leakage currents, we have recently introduced a modification of this method, by using a metal-insulator-semiconductor (MIS) sample structure for the TSC experiment (MIS-TSC)[3]. The use of the MIS structure allows for a true unipolar high-resolution trap state evaluation,  low leakage currents (jleakage< 1 fA/cm2), and avoids charge carrier recombination due to unipolar trap filling.

To distinguish between defect states in the perovskite bulk and metal-induced interface trap states, we have investigated devices using different metals (Ag, Au and Ni) as top contacts. We detect characteristic trap states independent of the contact metallization, which are probably related to the defect states in the perovskite bulk and are in line with the current literature. We demonstrate further, that the type of top metallizations strongly influences trap states at the MAPI/metal interface. While the formation of hole and electron trap states with low activation energy was observed for Ag contacts, the formation of deeper trap states in the range of 400 meV for electrons and 1400 meV for holes was detected for MAPI/Au and MAPI/Ni interfaces.

The authors acknowledge financial support through the European Union in the Leitmarktwettbewerb NRW: Neue Werkstoffe, within the PeroBOOST project (EFRE-0800120; NW-1-1-040).

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