Detection and Characterization of Defect States in Organometallic Halide Perovskites
Aleš Vlk a, Jakub Holovský a b, Zdeněk Remeš a, Lucie Landová a b, Martin Ledinský a
a Laboratory of Nanostructures and Nanomaterials, Institute of Physics, ASCR, 162 00 Prague, Czech Republic
b Centre for Advanced Photovoltaics, Faculty of Electrical Engineering, Czech Technical University, Prague, Czech Republic, Technická, 2, Czech Republic
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#PERInt19. Interplay of composition, structure and electronic properties in halide-perovskites
Berlin, Germany, 2019 November 3rd - 8th
Organizer: Pablo P. Boix
Poster, Aleš Vlk, 334
Publication date: 18th July 2019

Organometallic halide perovskites have in recent years become due to their interesting optoelectronic properties a subject of intense research. The emphasis is on a development of high-performance photovoltaic cells nowadays reaching efficiencies over 23 %.[1] To acquire better understanding on how these materials reach the remarkable power conversion efficiencies the absorption spectra and namely the defect states, has to be studied. For this purpose, different spectroscopic techniques as Fourier transform photocurrent spectroscopy (FTPS), photoluminescence spectroscopy (PL) or photothermal deflection spectroscopy (PDS) was used.[2,3] Such complex approach to this problematic give us a powerful tool in studies of defect states in organometallic halide perovskites.

The minimal voltage deficiency (WOC, defined as the difference between open circuit voltage, VOC, and bandgap, EG/q) is good indicator of defect states quantity. Methylammonium lead bromide (MAPbBr3) based photovoltaic cells have in general high WOC. For record photovoltaic cell with VOC  = 1,65 V is WOC  = 0,67 V which suggest large density of defect states which is the reason why we chose this material for our study.[4,5] 

In this work we present a comparison of an absorption spectra of MAPbBr3 single crystal obtained by FTPS, PL and PDS. This comparison shows a significant difference in the absorption spectra obtained using different methods and experimental conditions such as applied voltage in FTPS or different detection and excitation spot in PL measurements. Using this approach, we were able to observe defect states with energy level E = 2.18 ± 0.02 eV. Comparing FTPS measurements with two different arrangements of contacts we were able to identify these defect states as bulk defect.

We acknowledge the support of Czech Science Foundation Project No. 17-26041Y, Operational Programme Research, Development and Education financed by the European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (Project No. CZ.02.1.01/0.0/0.0/16_019/0000760 - SOLID21 and No. CZ.02.1.01/0.0/0.0/15_003/0000464 - Centre of Advanced Photovoltaics).

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