[Background introduction]

Metal halide perovskite semiconductor materials exhibit significant superior properties in solar cell, photodiode, sensor and other optoelectronic devices. Low-dimensional and nano-structured materials often give the material room to further expand the application. For example, the two-dimensional perovskite structure can effectively improve the stability of the perovskite solar cell, thereby greatly promoting the commercialization process of the perovskite solar cell. The zero-dimensional quantum dot perovskite structure not only has higher perovskite phase stability, but also has more ion-regulating properties of perovskite materials. In addition, the controllability of the surface groups of the perovskite quantum dots enables a device structure that cannot be realized in a perovskite thin film battery deposited by a solution method.

[Introduction]

Recently, the Joseph M Luthur team of the National Renewable Energy Laboratory of the United States and the team of Prof. Zhang Minghui and Professor Li Guoran from Nankai University collaborated to prepare a perovskite absorber layer composed of different quantum dot layers by layer-by-layer deposition method. By introducing the heterostructure inside the perovskite layer, the separation and collection of electrons and holes are effectively improved, and the influence of the heterojunction position and the composition of each layer of quantum dots on the photovoltaic performance is explored. This paper describes a heterostructure that can effectively improve the performance of perovskite solar cells. The photoelectric conversion efficiency of the stabilized output of the assembled perovskite quantum dot solar cells can reach 15.74%.

The related research was published in Nature Communication. The first author of the thesis is Zhao Chuang, a doctoral student of CSC of Nankai University. The author of the communication is Joseph M Luthur, National Renewable Energy Laboratory.

[Graphic introduction]

Firstly, a perovskite film composed of different quantum dot layers was prepared by using the unique layer deposition method of quantum dots. The existence and stability of the interface of different quantum dot layers in the perovskite film were verified by ToF-SIMs. Sex (Figure 1). The quantum dots of each component were characterized by XPS and UPS, and the energy level structure of the perovskite quantum dots was obtained. Then the internal heterostructure of the perovskite quantum dot film was designed to realize electrons and holes. Effective separation and transmission (Figure 2). By utilizing the heterostructure in the perovskite film and optimizing the heterojunction position and its quantum dot composition, a perovskite quantum dot solar cell with a photoelectric conversion efficiency of 15.74% was assembled (Fig. 3 ). In order to further explore its working mechanism, the transient spectroscopy test of the perovskite film with heterojunction (Fig. 4) verified that the heterostructure can improve the separation and collection of electrons and holes in the perovskite film. The short-circuit current of the perovskite quantum dot solar cell is improved, thereby improving the photoelectric conversion efficiency of the device.

Figure 1 Heterostructure in a perovskite quantum dot film

  

a, Schematic representation of a perovskite light absorbing layer having an internal heterojunction deposited by layer-by-layer deposition using different quantum dots. B-d, the structure is CsPbI3/TiO2 (b), CsPbI3/Cs0.25FA0.75PbI3/TiO2 (c) and Cs0.25FA0.75PbI3/CsPbI3/TiO2 (d) ToF-SIMs.

Fig. 2 Optical and electrical properties of the internal heterojunction of perovskite quantum dot film



a, energy level diagrams of perovskite quantum dots of different compositions and other layers in the solar cell. b, EQE of perovskite quantum dot solar cells with internal heterojunctions at different locations. c, EQE of perovskite quantum dot solar cells using internal heterojunctions of different underlying component quantum dots.

Figure 3 Photovoltaic performance of perovskite quantum dot solar cells



a, a cross-section STEM-HAADF of a perovskite quantum dot solar cell, the structure of which is Glass/ITO/TiO2/Cs0.25FA0.75PbI3/CsPbI3/spiro-OMeTAD/MoOx/Al. B-c, the thickness ratio of the different Cs0.25FA0.75PbI3 quantum dot layer to the CsPbI3 quantum dot layer in the internal heterojunction, the JV curve of the device and the stable output efficiency at 0.95V. D-e, in the inner heterojunction, the bottom layer uses different quantum dots, the JV curve of the perovskite quantum dot solar cell and the stable output efficiency at 0.95V.

Table 1 Photovoltaic performance parameters of perovskite quantum dot solar cells



The thickness ratio of the different Cs0.25FA0.75PbI3 quantum dot layer to the CsPbI3 quantum dot layer was used in the internal heterojunction, the JV curve of the device and the parameter of the stable output efficiency at 0.95V.

Figure 4: Transient absorption spectra of perovskite quantum dot heterojunction films



a, the transient absorption spectrum of the heterojunction film b, the structure diagram of the heterojunction film in the perovskite quantum dot. c Transient absorption spectrum of a perovskite quantum dot heterojunction film excited from the Cs0.25Fa0.75PbI3 layer. D-e is the relationship between the spectral signal decay time and the composition ratio of the perovskite quantum dot heterojunction film excited from the CsPbI3 layer and the Cs0.25Fa0.75PbI3 layer, respectively. F-g, transient absorption spectra of CsPbI3 and Cs0.25Fa0.75PbI3 perovskite quantum dot films, respectively.

Literature link: https://www.nature.com/articles/s41467-019-10856-z

Source: material cattle