Based on the characteristics of high conductivity, hydrophilicity and pseudocapacitance, two-dimensional Ti3C2TX MXene nanosheets have been widely studied in the fields of solar cells, zinc ion capacitors, and sensors. SnO2 is a common wide-bandgap semiconductor. Due to its low-temperature preparation characteristics, it has the potential to be used in future flexible devices. However, it is necessary to optimize the material and improve the structure to achieve the best photoelectric performance. Although TiO2 has been reported to form a heterojunction with SnO2, the preparation of anatase TiO2 generally requires higher temperatures or complicated processes, which restricts the application of SnO2. At this stage, anatase-type TiO2 can be formed on MXene through hydrothermal reaction or high temperature. In order to further effectively combine with SnO2, it is still necessary to explore low-temperature preparation processes to effectively compound MXene, TiO2 and SnO2, in order to better play the overall better performance.

Low‑Temperature Growing Anatase TiO2/SnO2 Multi‑dimensional Heterojunctions at MXene Conductive Network for High‑Efficient Perovskite Solar Cells

Linsheng Huang, Xiaowen Zhou, Rui Xue, Pengfei Xu, Siliang Wang, ChaoXu, Wei Zeng*, Yi Xiong*, Hongqian Sang, Dong Liang

Nano‑Micro Lett.(2020)12:44

https://doi.org/10.1007/s40820-020-00379-5

Highlights of this article
1. Construct a nano-scale multi-dimensional heterojunction network based on two-dimensional MXene edges; 2. Prepare anatase-type TiO2/SnO2 heterojunction by low-temperature controllable annealing; 3. Construct a perovskite solar cell with high energy conversion efficiency And high moisture resistance stability.

brief introduction

The Zeng Wei research group of Anhui University cooperated with the Xiong Yi research group of Wuhan Textile University. In this article, a low-temperature annealing process and the application of the generated multi-dimensional heterojunction conductive network in perovskite solar cells are reported. Through the controlled low-temperature annealing method in air and nitrogen, based on the oxygen vacancy contention effect, zero-dimensional TiO2 quantum dots are grown in situ on the edge of the two-dimensional Ti3C2TX MXene sheet, and the zero-dimensional quantum dots and three-dimensional SnO2 particles are firmly combined to form a Unique multi-dimensional heterojunction conductive network. When applied to the electron transport layer of a perovskite battery, the introduction of this multi-dimensional heterojunction not only effectively improves the optical properties of the electron transport layer, but also improves the crystallinity and internal interface of the upper perovskite, which is an internal carrier The large-scale transmission provides an effective nano-transmission network. This makes the photoelectric conversion efficiency of the perovskite solar cell rise from 16.83% to 19.14%, and it can maintain 85% of the performance for more than 45 days in air with a humidity of 30%-40%, and has negligible hysteresis. So as to provide ideas for the controllable construction of heterojunction and the improvement of optoelectronic devices.

Graphic guide

I Preparation of multi-dimensional heterojunction film
The multi-dimensional heterojunction film is grown on the FTO substrate by spin coating and controlled annealing process. First, the FTO substrate is cleaned by ozone, then the SnO2-MXene mixed precursor solution is spin-coated, and then annealed on a hot stage. During annealing, annealed in air for 5 minutes, and then annealed in nitrogen for 25 minutes, to form a multi-dimensional heterojunction film with effective composite of MXene, TiO2 and SnO2.
 
Figure 1. Process flow for the preparation of multi-dimensional heterojunction film and perovskite layer.
II Characterization and analysis of multidimensional heterojunction films
When the multi-dimensional heterojunction film was analyzed by scanning electron microscope (SEM), it was found that MXene was sparsely attached to the surface of SnO2, showing a typical sheet-like morphology. Through X-ray energy spectrum analysis (EDS), it was found that the film was mainly composed of Sn. It is composed of O, C and Ti, and the elements are evenly distributed.
Figure 2. (a) SEM top view of the multi-dimensional heterojunction film, the inset is an enlarged view of the dotted area; (bg) the EDS image of the multi-dimensional heterojunction film, (b) the SEM image of the analysis position, (c) the element analysis The layer images, (dg) are the mapping images of Sn, O, C and Ti elements respectively. X-ray diffraction analysis of the multi-dimensional heterojunction film found anatase phase TiO2, and further comparison and analysis by X-ray photoelectron spectroscopy (XPS) showed that a small amount of Ti element and the chemical bond of Ti4+ exist in the multi-dimensional heterojunction film The content is significantly higher than that in pure MXene, which indicates that the controlled annealing process has successfully converted other Ti bonds in MXene into Ti4+ bonds. In addition, some Ti-O bonds are also found, which indicates that in the multi-dimensional heterojunction film, tin-based The oxides combine with a small amount of titanium-based oxides, resulting in the effective formation of a multi-dimensional heterojunction network.