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UEC Int’l Mini-Conference No.52 43

The Study of Effects of Tin (II) Iodide Mixed in Lead Halide Ligand

Solution for Solar Cell Applications

Napasuda WICHAIYO , Yuyao WEI, and Qing SHEN
∗
Department of Engineering Science
The University of Electro-Communications
Tokyo, Japan

Keywords: PbS colloidal quantum dots, Lead halide ligand, Surface passivation, Colloidal quantum
dot solar cells

Abstract
Surface passivation is essential for optimizing the efficiency and stability of lead sulfide (PbS) col-
loidal quantum dots (CQDs) in solar cell applications. PbS CQDs are particularly impressive semi-
conductor materials due to their adjustable optical band gap, which can be controlled by the QD size
to match the infrared spectra wavelength range. These quantum dots can exhibit n-type or p-type
semiconductor properties through doping mechanisms involving surface ligands. However, doping tech-
nology is challenging due to the natural self-purification tendency of nanocrystals. This research aims
to explore the characteristics of n-type PbS CQDs, particularly their optical and electrical properties,
by investigating the effect of tin iodide (SnI 2 ) on surface passivation. One of the major issues in devel-
oping efficient CQDSCs is improving surface passivation, which is critical for decreasing surface defects
that lead to poor current density and open-circuit voltage. In this research, we have proposed a new
surface passivation technique to enhance the surface passivation of PbS CQDs by mixing tin (II) iodide
(SnI 2 ) into a lead halide (PbX 2 ) ligand solution through a solution-phase ligand exchange technique.
We systematically varied the concentration of SnI 2 in a lead halide ligand solution and utilized this
mixture for the surface passivation of PbS CQDs. Herein, our findings indicate that increasing the
SnI 2 concentration significantly reduces the defect peak observed in the photoluminescence (PL) spec-
tra of PbS-PbX 2 samples, resulting in narrower PL spectra. These observations are further supported
by PL decay curve and Stokes shift analyses, which demonstrate that higher SnI 2 concentrations en-
hance surface passivation, thereby mitigating surface defects and enhancing optoelectronic properties.
The improved passivation achieved through SnI 2 treatment has the potential to raise power conversion
efficiency and stability in CQDSCs, revealing the path for further advancements in this field.

The author is supported by (MICH) MEXT Scholarship.
*