FABRICATION OF ORGANIC/INORGANIC LEAD HALIDE BASED PEROVSKITE SOLAR CELL UNDER AMBIENT CONDITIONS

Abstract

With respect to continuous population growth and industrialization, energy demand of today’s life is continuously growing. As it is well known, the supply of fossil fuels is dwindling and other concerns like impact on climate change and global warming are looking towards feasible resources of renewable energy. Among all the renewable energy resources, solar energy is the world's most abundant, clean, and promising candidate. Currently, photovoltaic industry is dominated by crystalline silicon solar cells (conventional photovoltaics). However, various drawbacks are associated with this technology such as requirements of highly pure crystalline silicon material, complex fabrication procedure, and installation cost. Therefore, to meet energy demands of society, it is necessary to develop eco-friendly conversion systems which utilize low cost raw materials and take the advantage of simple and inexpensive fabrication approaches. Recently, organic-inorganic hybrid metal halide perovskite solar cells (PSCs) have been drawn much attention due to their photovoltaic performance. The power conversion efficiency of PSC has grown quickly from 3.8% to as a certified value of 23.7% within a short span of 9 years. Therefore, rapid growth in photovoltaic performance of lead halide-based perovskite solar cells has made them a potential candidate for emerging solar technology. However, moisture stability of these perovskite materials is very critical issue, which blocks its roadmap for commercialization. To overcome this issue, we have developed a simple and cheap way in which any encapsulate material like PMMA, epoxy, etc., is not required to protect PSCs from surrounding moisture. In this approach, barium (Ba) doping (1.0, 2.0, 5.0, 10.0, and 20.0 mol%) with pristine perovskite (CH3NH3PbI3) was done, which plays crucial role to improve the long-term ambient stability of fabricated device. The long-term stability of fabricated devices was observed under ambient conditions with relative humidity range of 35% to 68%. An optimum concentration of 2.0 mol% Ba doped perovskite film-based PSC exhibited higher ambient stability as compared to pristine perovskite-based PSC. With 20 days systematic photovoltaic study under air atmosphere, it was found that 2.0 mol% Ba doped perovskite based device maintains ⁓ 92.0% of initial PCE, while, pristine PSC maintains only ⁓ 29.0% of initial PCE. Therefore, obtained photovoltaic performance after 20 days of initial fabrication of devices revealed a significant improvement in long-term ambient stability of PSCs without any encapsulated/passivated materials. iv | P a g e Additionally, as perovskite material itself can be manufactured at low temperatures, which makes it attractive for low cost manufacturing. TiO2 has been extensively used as an ETL in the fabrication of PSCs. However, elevated temperature processing is required for fabrication of TiO2 film, which is not feasible with fabrication of device at flexible substrate. So, in this regard, we have introduced a low temperature solution processed SnO2 as an effective compact ETL for the fabrication of PSC under humid conditions. The device efficiency of SnO2 based PSC was found to be 8.51% under ambient conditions. It has been observed that fabricated low temperature solution processed metal oxide ETL exhibited low electron conductivity, which has still forbidden the device performance. To address this issue, a small amount of metal doping with pristine metal oxide film and followed by low temperature annealing process, is an efficient way to improve the electrical properties of metal oxide film that leading to higher photovoltaic performances of device. An optimal Mo concentration of 1.0 mol% exhibited PCE of 10.52% with 71.10% of FF, when processed in the ambient with an average relative humidity range of 65% to 75%. Our photovoltaic results indicate that low temperature processed Mo doped SnO2 as an ETL is applicable for a fully automated and cost-effective fabrication of PSCs.