Flexible solar cells have attracted tremendous interest because of their outstanding properties of flexibility, portability, and light weight. These features offer promise for applications in such areas as wearable power sources, building-integrated photovoltaics, and aerospace. Perovskite is considered an ideal material for preparing flexible solar cells because most perovskite thin films and matched hole transport layers (HTLs) can be fabricated at low temperatures (< 150 ℃). However, for the electron transport layer (ETL) to increase the crystallinity and conductivity of SnO2, a relatively high temperature is typically required (> 180 ℃). A high temperature such as this will cause deformation to flexible substrates. Therefore, one bottleneck for highly efficient flexible perovskite solar cells (f-PSCs) is to realize high-quality ETLs at low temperatures.
Recently, a group led by Prof. Yiqiang Zhan from Fudan University reported high-efficiency f-PSCs by annealing a SnO2 ETL in a rough vacuum at a low temperature (100 ℃), and the best f-PSCs efficiency of 20.14% was obtained. SnO2 layers that have been prepared by this method have shown higher roughness and hydrophobicity in comparison with samples prepared in an air atmosphere and temperatures of 100 °C, leading to an improved ETL/perovskite interface connection and reducing defects in the SnO2/perovskite interface. The appropriate density of oxygen vacancies on the surface during this treatment can be responsible for higher conductivity, which is beneficial for charge transfer.
This work suggests that, in addition to high-temperature annealing, the control of oxygen partial pressure is also effective in achieving high conductivity for metal oxides even at low temperatures, which is meaningful for flexible electronics.
When a vacuum-assisted annealing method in SnO2 electron transport layer fabrication at a low temperature (100 ℃) was utilized in this study, a remarkable open circuit voltage (1.14 V) and efficiency (20.14%) were achieved for PSCs with polyethylene terephthalate flexible substrates.
The Journal of Energy Chemistry is a publication that mainly reports on creative researches and innovative applications of chemical conversions of fossil energy, carbon dioxide, electrochemical energy, and hydrogen energy, as well as the conversions of biomass and solar energy related with chemical issues to promote academic exchanges in the field of energy chemistry and to accelerate the exploration, research and development of energy science and technologies.
Journal of Energy Chemistry