High Performance Flexible Perovskite Solar Cells on Flexible Glass Substrate

In the last decade, metal halide perovskites have garnered significant attention as a promising class of photovoltaic (PV) materials. Rapid advancement and breakthroughs have seen the PCE rise from 3.8% to 26.7%. The rapid progress of this field brings increased demands for developing building integrated, portable and wearable solar cell devices. Hence recent research efforts are targeted towards exploring new substrates and structures capable of supporting flexible characteristics. Flexible perovskite solar cells (F-PSC) lead the way to the commercialization of PSC on non-flat surfaces. Successful fabrication of highly efficient flexible PSC can significantly diversify the application of solar cells. As a result, the development of F-PSCs represents a critical advancement for the field of PSC.
However, the development of F-PSC has been limited due to some critical challenges. First is the choice of a suitable flexible substrate. For successful application in F-PSC an ideal substrate should have high transmittance, excellent flexibility, high thermal stability and low surface roughness. It is challenging to find a single material that fulfills all the requirements. Another major challenge is the need for low processing temperature for crystallization of transparent conductive layer. The traditional conductive oxide layer such as FTO and ITO are not compatible with flexible substrates due to their brittle nature. Deposition of alternative TCO layer requires high temperature annealing for crystallization. However, the flexible substrates often lose their flexibility when thermally annealed at temperatures greater than 200^oC.
In this work we report the use of thin flexible willow glass as substrate material. Flexible willow glass has high transmittance, good flexibility and more thermal stability than polymer substrate material such as PET and PEN which have low glass transition temperature. Further, prior research indicates that the optical transmission of glass substrates, particularly in the UV regime, improves as thickness decreases. This observation highlights the potential for performance enhancement in PSCs fabricated on thin glass substrates through the integration of anti-reflective coatings (ARCs).
We use a highly conducting and transparent Zn doped In₂O₃ (IZO)-Ag-IZO (IAI) layer on flexible willow glass. IAI layer comprises of transparent 40nm thick IZO layers on either side of a conducting 8nm thick Ag layer. As a result, the final structure is both transparent and conducting making it suitable for use as TCO. Multilayer oxide/metal/oxide (OMO) such as IAI has been examined as a transparent electrode of solar cells. While this multilayer film can be deposited at low temperature and provide electric conductivity and optical transparency, there is an inherent limitation in improving both electric and optical performances. In this study, we explored a unique low temperature process to address such inherent limitation of IAI transparent electrode.
Our flexible solar cells are also implemented with micro-textured PDMS-based antireflection coating (ARC) film which contains Si nanoparticles (NPs) and silicate-based inorganic phosphors (SIP). SiO₂ NPs enhance diffuse transmittance through multiple Mie scattering, leading to less reflectance and longer optical path of the flexible solar cells. On the other hand, SIP particles effectively convert UV light to visible light, thereby preventing the UV-induced degradation and parasitic absorption of the flexible solar cell. Such optical managements enhance not only the power conversion efficiency but also the stability of the flexible solar cells.
In addition to the device performance, this presentation will report detailed mechanisms underlying low temperature process of IAI and optical management of our unique ARC will be discussed.