Ferrocene Interlayer for a Stable and Gap-Free P3HT-Based Perovskite Solar Cell as a Low-Cost Power Source for Indoor IoTs

Abstract

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).