Supplementary Material
Electrical field profile and doping in planar lead halide perovskite solar cells
Antonio Guerrero1, Emilio J. Juarez-Perez1, Juan Bisquert1,2, Ivan Mora-Sero1,
and Germà Garcia-Belmonte1,*
1 Photovoltaic and Optoelectronic Devices Group, Departament de Física,
Universitat Jaume I, ES-12071 Castelló, Spain
2 Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
Calculation of eTiO2
Devices in the configuration FTO/TiO2/Au were prepared and the Capacitance-Voltage response was measured (Figure SI1). The dielectric constant was calculated following equation (1) where L is the thickness of the TiO2 layer, A is the area and e0 the vacuum permittivity. Considering the capacitance value at 0 V and the thickness measured by a VEECO DEKTACK 6M Stylus Profiler values of dielectric constant as those shown in. Table SI1 are obtained. The dielectric constant of the TiO2 is consistent with a variation of the TiO2 thickness.
, (eq.1)
Figure SI1: Capacitance-Voltage response of devices prepared in the configuration FTO/TiO2/Au.
TiO2 thickness[nm] / Capacitance @ 0 V
[mFcm-2] / e
40 / 0.39 / 18.0
110 / 0.17 / 21.5
Table SI1: Summary of calculated eTiO2 for devices in the configuration FTO/TiO2/Au
Frequency selection for Mott-Schottky analysis
Full Impedance Spectroscopy measurements were carried out for all devices. Capacitance-Frequency plot and Nyquist plot are shown in Figure SI2 of a representative reference device with the configuration FTO/TiO2/PVK/spiro-OMeTad/Au. Capacitance vs Frequency plots show a plateau in the range of 100 Hz to 10 kHz. In order to reduce the measurement time of Capacitance-Voltage a fixed frequency of 600 Hz can be selected to carry out the analysis. By using this method degradation of the devices during the electrical test is kept to a minimum as evidenced by the J-V curves before and after the C-V measurements.
Figure SI2: Capacitance vs Frequency plot (top graph) of a reference device measured under dark conditions. Nyquist plots of two representative applied DC voltages. The Mott-Schottky behavior is observed in the high frequency region of the spectra.
Experimental details KPFM
Kelvin Probe Force Microscopy (KPFM) experimental scheme is illustrated in the main text. Analysis by Scanning Electron Microscopy of a representative device is shown in SI3a. The image shows that the thickness of the perovskite layer is about 450 nm. The same device is analyzed by KPFM. A topographic AFM image presents a smooth cleaved surface of the cross-sectional device (Figure SI3b). The individual potentials of each of the layers stack can be imaged into their respective potential levels by KPFM scanning (Figure SI3c). A mean-field contact potential difference (CPD) of the complete stack is drawn from averaged cross-sectional field of 7 individual profiles. A single cross section profile is represented by the red line in Figure SI3. By measuring vacuum level variations relative to Fermi level positions in Kelvin probe configuration, the CPD represents an internal potential distributions of the device when the Fermi level aligns in an equilibrium energy level.1
Figure SI3: a) Cross-Section Scanning Electron Microscopy image of a representative device in the configuration FTO/TiO2/PVK/spiro-OMeTad/Au. Cross-section measurements in AFM mode b) and KPFM mode c) of the same device shown in a).
References
1. J. Lee, J. Kong, H. Kim, S.-O. Kang and K. Lee, Applied Physics Letters, 2011, 99, 243301.