An idea that has attracted much attention in this current digital revolution is the possibility to add sensors and intelligence to basic objects to allow them to collect real-time data without involving a human being and share it through the internet to anyone in the entire world. These devices are known as Internet of Things (IoT), and their production has been growing exponentially, creating a massive web of interconnected devices. A significant portion of these new devices is used indoors in which wireless power is supplied by a battery. In these cases, the range and frequency of data transmission is usually curtailed to achieve sufficient battery life, and there’s an additional maintenance cost for the periodical replacement of the battery. A more promising energy supply alternative is indoor photovoltaics (IPV), which harvests ambient light and converts it into electricity, providing greater reliability and operational lifetimes in wireless sensor networks. Perovskite Solar cells have shown to be a promising IPV technology, owing to their advantages of simple fabrication technology, adjustable bandgap, high absorption coefficient, long carrier lifetime, and low recombination rate, which results in a high performance under low-light conditions.
Here, we report a highly efficient and flexible PSC, both with a metal and a carbon electrode (the latter with and without HTM). A maximum efficiency of 30.9 % at 1000 lux (393.6μW/cm2) and 30% at 200 lux (76.4μW/cm2) was obtained for the metal-based configuration, whereas the carbon-based devices with and without P3HT presented a maximum efficiency of 25.4% and 23.1% at 1000lux and 24.7% and 22.3% at 200lux, respectively. To the best of our knowledge, these values are the record efficiency values for flexible indoor perovskite solar cells, for all three configurations: metal-based, carbon-based and carbon-based HTM-free. The perovskite composition was selected in order to maximize the bandgap while ensuring a highly stable and halide-segregation resistant formulation. Impedance spectroscopy, suns-Voc, transient-photocurrent decay, and transient-photovoltage decay measurements were performed on the three configurations to have a better understanding on the charge carrier’s extraction efficacy. Furthermore, HTM-free carbon-based configuration presented a high operational and thermal stability, retaining 84% of its initial efficiency after 1000h at MPPT under 0.6sun, and keeping virtually the same performance after 1000h at 85°C, whereas the P3HT+carbon and gold configurations lost 16% and 13% of their initial efficiency aft after the thermal test, respectively.