Periodic Reporting for period 1 - HES-PSC-FCTL (High efficiency and stability perovskite solar cells based on the functionalized charge transport layers) Reporting period: 2019-08-01 to 2021-07-31 Summary of the context and overall objectives of the project Efficient and stable solar cell technology has become important means to solving the growing energy and environmental crisis. It has been found to be central to the high-efficiency solar cells that the judicious selection of appropriate charge transport layers. In this work, we fabricated a high-efficiency and stable inverted planar perovskite solar cell, which employed a Lanthanum (La)-doped BaSnO3 (LBSO) / graphene bi-layer as the electron transport layer. Based on “LBSO-template induced perovskite re-nucleation and crystal growth”, the stability and efficiency of our devices have been improved. Through this project, we find a new route to boost the charge carrier collection efficiency and enhance the stability of perovskite. These results are conducive to speeding up the process of the practical application of perovskite solar cells, thereby promoting the development and the application of clean energy. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far In this two years project, we finished the five independent but close related work packages and reached the major milestones: 1) we optimized the nanoparticle particle size, doping concentration and film thickness of the bi-functional layer film, resulting in a 5% increase in device efficiency related to the reference solar cell (same batch). 2) The stability of the perovskite solar cells with the LBSO layer has been improved by keeping 95% initial efficiency after 800 h. That is four-time than that of the reference device. The LBSO-template induced perovskite re-nucleation and crystal growth enhanced the quality of the perovskite/transport layer interface. 3) The degradation mechanism of perovskite solar cells has been researched. Our result reveals the quality improvement of the interface can depress the device performance degradation. Part of the works has been published in top peer-review journals, such as Nano Energy (DOI: 10.1016/j.nanoen.2020.105249) Advanced Materials (DOI: 10.1002/adma.202006435) and Energy & environment materials (DOI: 10.1002/eem2.12231). Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) We found that the quality of the perovskite interface has an important influence on the performance of the devices, especially for stability. The interface improvement induced by the LBSO layer has been further verified and highlighted in the ageing test. Our research work provided a feasible technical route to improve the efficiency and stability of perovskite solar cells. This bi-functional LBSO layer can also be fabricated through a large-scale coating method (slot-die coating and blade coating), which can play an important role in the commercialisation of perovskite solar cells. We have communicated with well-known photovoltaic companies (Jinkosolar and CanadianSolar) on this technology and aroused their great interest. Although this project has ended, the researcher will continue to cooperate with collaborators to promote the industrialisation of project results.