A major industrial application of perovskite photovoltaic cells will be large area fabrication of extremely lightweight flexible power sources in demand of electric vehicles and self-charging small devices in IoT society. Such application is not easy for Si solar cell, in particular for the purpose of power devices useful under weak indoor light. Perovskite solar cell capable of high voltage output can work with high performance even under very low light intensity. We fabricated Cs-doped FAMA perovskite photovoltaic cells on glass substrate  and plastic film substrate (125 um); the latter works with efficiency 15-18% exhibiting relatively small ideality factor <1.5 in intensity dependence of Voc . The cell maintains high voltage under indoor illumination, indicating the usefulness of the device as power source to the circuitry of wireless IoT devices. The plastic film perovskite device showed robust stability against mechanical bending over 1000 times. Device was fabricated by low temperature preparation of metal oxide electron transporting layer (ETL). By tuning the composition of ETL at junction structure, hysteresis was successfully removed. Heat-resistant and hydrophobic hole transport materials replaced spiro-OMeTAD to improve the device stability against ambient air and long-term light exposure. We focused on use of low temperature-prepared AM-free FA/Cs perovskite absorber in glass-based and plastic-based cells to enhance thermal resistance. The FA/Cs P3HT perovskite cell was tolerant of large temperature changes (-80 to +100C). The device durability against thermal impacts is a significant issue in R&D but it is improving by tuning the perovskite and hole transporting materials. Perovskite cells were also subjected to stability examination against exposure to high energy particle radiation such as electron and proton for the purpose to know radiation tolerance in comparison to Si, GaAs-based commercial solar cells. Based on these data, versatile applications of lightweight perovskite photovoltaic devices in IoT and smart sustainable system industries will be discussed.
 T. Singh and T. Miyasaka, Adv. Energy Mat. 2017, DOI: 10.1002/aenm.201700677
 T. Singh and T. Miyasaka, submitted.