Preparation Of PbS And CH₃NH₃PbI₃ Thin Films Based On Lead Xanthate Precursors And Its Opto-electronic Properties

In recent years, with the development of material science, semiconductor thin film technology has been developed rapidly and semiconductor thin films have been widely used in many fields due to their unique properties and excellent performance,and the research of thin film technology has become one of the most active interdisciplinary subject in vacuum, microelectronics and materials science.Microstructure control is critical to achieve high performance for thin film-based devices. In this paper, the main aim is to prepare the PbS thin films and CH₃NH₃PbI₃ thin films with high quality based on lead xanthate compounds.In the first section, the PbS thin films were prepared via in-situ thermal decomposition of lead xanthate compounds and the microstructure and performance of PbS thin films were modulated by self-assembling monolayer?SAM?. In the traditional preparation method, “island” like structures are usually obtained mainly due to the non-uniform nucleation. To improve the microstructure of PbS thin films,herein, self-assembling monolayer was used as an efficient approach to solve the critical concern of non-uniform nucleation in in-situ thermal decomposition of lead sulfide?PbS? that were fabricated through the thermal decomposition of lead xanthate precursors on the modified ZnO-coated substrates with 3-mercaptopropionic acid?MPA? SAM. Firstly, the effect of the precursor concentrations and solvents on the microstructure of PbS thin films was investigated and the preparation conditions were optimized. And then, the characteristics of PbS films, including crystalline structure,surface morphology and optical absorption property were investigated to reveal the modulating effect of MPA under the optimized preparation condition. The results showed that high-quality PbS thin films with reduced pin-holes and uniform crystalline grains were fabricated with the incorporation of MPA. More importantly,PbS thin films modulated by MPA showed better photoelectric response.Secondly, in recent years, organic-inorganic hybrid perovskite?CH₃NH₃PbI₃,CH3NH3Pb3-x Clx, NH2CH=NH2PbI3? solar cells have become a new star in the third photovoltaic technology due to its advantages of the direct band gap, the highabsorption coefficient, the low exciton binding energy, long exciton and charge carrier diffusion distance, low cost, simple preparation process, high power conversion efficiency, and easy to realize the large area flexible devices. Previous studies have indicated that different lead sources can be used as precursors to effectively control the forming process of the perovskite. To achieve the high-performance, it is necessary to obtain the CH₃NH₃PbI₃ thin films with high quality. In this section, the lead-xanthate complexes, as a new lead source, were applied to prepare CH₃NH₃PbI₃ thin films via the one-step spin-coating method.Compared to the lead iodide?PbI2?, the surface coverage of CH₃NH₃PbI₃ thin film has been improved, and the morphology is significantly different. However, there still exist some pin-holes, resulting in the decrease of optical absorbance and the increase of the leakage current path, thereby undermining the device performance. In order to further optimize the preparation process, we use a simple heat treatment method to decreases the conversion rate to obtain the CH₃NH₃PbI₃ thin films with good crystallinity, uniform and better photoelectric properties. This work provides a new way to control the morphology of CH₃NH₃PbI₃ thin films, and meanwhile to provide a new method for the preparation of CH₃NH₃PbI₃ thin films with high quality and good reproducibility.