posted on 2022-03-31, 13:39authored bySyeda Qudsia, Staffan Dahlström, Christian Ahläng, Emil Rosqvist, Mathias Nyman, Jouko Peltonen, Ronald Österbacka, Jan-Henrik Smått
Titanium dioxide
(TiO2) is a commonly used electron
selective layer in thin-film solar cells. The energy levels of TiO2 align well with those of most light-absorbing materials and
facilitate extracting electrons while blocking the extraction of holes.
In a device, this separates charge carriers and reduces recombination.
In this study, we have evaluated the hole-blocking behavior of TiO2 compact layers using charge extraction by linearly increasing
voltage in a metal–insulator–semiconductor structure
(MIS-CELIV). This hole-blocking property was characterized as surface
recombination velocity (SR) for holes
at the interface between a semiconducting polymer and TiO2 layer. TiO2 layers of different thicknesses were prepared
by sol–gel dip coating on two transparent conductive oxide
substrates with different roughnesses. Surface coverage and film quality
on both substrates were characterized using X-ray photoelectron spectroscopy
and atomic force microscopy, along with its conductive imaging mode.
Thicker TiO2 coatings provided better surface coverage,
leading to reduced SR, unless the layers
were otherwise defective. We found SR to
be a more sensitive indicator of the overall film quality, as varying SR values were still observed among the films
that looked similar in their characteristics via other methods.