Ferrocene Interlayerfor a Stable and Gap-Free P3HT-BasedPerovskite Solar Cell as a Low-Cost Power Source for Indoor IoTs

Although poly(3-hexylthiophene-2,5-diyl) (P3HT) with its stability-boosting hydrophobic surface is a promising low-cost alternative dopant-free hole transport material for n-i-p perovskite solar cells (PSCs), the P3HT-based PSCs suffer from surface energy mismatch between hydrophilic perovskite and hydrophobic P3HT, which results in interlayer gap, poor electronic contact, and poor charge extraction. In this study, low-cost ferrocene (Fc) acts as an interlayer at the perovskite/P3HT interface, inducing the replacement of the hydrophobic edge-on stacking of alkyl side chains with the hydrophilic π–π stacking of thiophene rings within the P3HT structure to mitigate such an energy mismatch. With an optimal amount of Fc, an average PCE of 23.6% has been achieved under indoor light at 1000 lux in comparison to 20.6% of P3HT-based PSCs without Fc. In addition, an unencapsulated device with the interlayer can retain 80% of initial PCE (T80) over 12 months in the dark with 70% RH, longer than T80 of 8 months without Fc. Finally, a Bluetooth sensor module is powered by three Fc-passivated P3HT-based PSCs connected in series to demonstrate the capacity of replacing batteries used for the Internet of Things (IoTs).