A green synthesis of CISe nanocrystal ink and preparation of quantum dot sensitized solar cells

Abstract

I–III–VI chalcopyrite copper indium selenium is one of therepresentatives of the light absorbing layer material, and is often used for a thin-film solar cell. With the development of nano-technology, CuInSe2 quantum dots (CISe QDs) which have intermediate belt and excitation effect characteristics are applied to the solar cells as an alternative of Cd- or S-based QDs. Most conventional methods for the synthesis of CISe QDs using solution involve the dangerous and environmentally unfriendly Oleylamine or phosphine coordination compounds. In this work, CISe QDs were synthesized by a green, safe and low-temperature method in triethylene glycol. Through controlling the growth temperature and time, the diameter can be adjusted from 3[Formula: see text]nm to 10[Formula: see text]nm. The samples exhibit quantum confinement effect, and have a controllable optical band gap. QDs were deposited on the surface of ZnO nanorods to obtain a photoanode, which were fabricated into quantum dot-sensitized solar cells. The device exhibits size-dependent performance. And the open circuit voltage shows a fluctuation up to 0.26[Formula: see text]V. When the size is 4[Formula: see text]nm, the short circuit current density is the largest (15[Formula: see text]mA/cm2).

Synthesis and Characterization of CdS/CISe Quantum Dots with Core–Shell Structure

“…[7,[26][27] Both electrons and holes are located in the lower bandgap shell material in the inverted-type I core-shell structure with a narrow bandgap semiconductor as the shell layer, which is beneficial to the transport and collection of carriers within the QDs. [8,[28][29][30][31][32] In recent years, CuInSe 2 QDs have been widely used in solar cells due to their photovoltaic properties, [33][34][35][36] and the efficiency of CISe for solar cells was not high in our group's previous studies. [35] Therefore, to obtain large volume quantum dots with low surface defect density and quantum confinement effect, we choose to use CISe QDs with small bandwidth as the shell material for the core-shell, and to reduce the degree of lattice distortion at the interface caused by the large difference in lattice structure between the core and shell materials, we choose to use CdS materials with relatively large bandwidth and small lattice mismatch with CISe as the core.…”

“…In recent years, CuInSe 2 QDs have been widely used in solar cells due to their photovoltaic properties, [ 33–36 ] and the efficiency of CISe for solar cells was not high in our group's previous studies. [ 35 ] Therefore, to obtain large volume quantum dots with low surface defect density and quantum confinement effect, we choose to use CISe QDs with small bandwidth as the shell material for the core–shell, and to reduce the degree of lattice distortion at the interface caused by the large difference in lattice structure between the core and shell materials, we choose to use CdS materials with relatively large bandwidth and small lattice mismatch with CISe as the core. In the case of bulk CdS/CuInSe 2 interfaces, the CdS valence‐band edge is lower than that in CuInSe 2 (energy offset = 0.02 eV), while the conduction‐band edge is lower in CuInSe 2 (energy offset = 1.2 eV).…”

“…The specific preparation method of the CISe QDs precursor solution can be read in the previous study. [35,37] After the precursor injection was completed, the precursors were kept at 190 °C for 10 min, cooled down to room temperature, and then washed with ethanol for preservation.…”

Green Synthesis of CdS/CISe Core‐Shell Structured Quantum Dots and Their Photovoltaic Applications

“…Although the prepared CdS/CISe core‐shell structured QDs have a low specific surface area, there is still an uneven particle dispersion in the samples, which leads to the aggregation of a large number of grains. [ 44 ] This situation is equivalent to the occurrence of crosstalk of quantum dots inside the device structure, which is unfavorable to the improvement of J sc . A suitable thickness of the CdS buffer layer favors the increase in the value of FF, which is mainly associated with the shunt resistance ( R sh ) of the cell.…”

“…In addition, charge recombination within the quantum dots can also lead to lower efficiency. [38,44] Although core-shell QDs exhibit a high fluorescence lifetime, the spin-coating method can result in an uneven film surface with voids present for solar cells. There may be some impurities and defects in the TiO 2 layer and absorption layer prepared by the spin-coated method, which makes the probability of the compounding of electrons and holes increase, and the compounding process is always accompanied by the directional movement of the carriers, which inevitably generates leakage currents and results in a decrease in efficiency.…”