Solvent-Tailored Carbon Paste for Effective Carbon-Based Perovskite Solar Cells

Abstract

Printable planar carbon electrodes present a cost-effective and highly promising alternative to thermally evaporated metals, serving as the rear contact for stable perovskite solar cells (PSCs). However, the power conversion efficiencies (PCEs) of the carbon-based PSCs (C-PSCs) are notably lower compared to those of state-of-the-art PSCs. The inferior contact between the carbon electrode and the underlying layer contributes to the performance loss. Here, we developed scalable doctor-bladed carbon electrode by simultaneously incorporating 4 wt% carbon black and utilizing toluene (TLE) solvent engineering to a commercial carbon paste, resulting in improved flexibility and conductivity while yielding reduction of resistivity by 50% measured via a 4-point probe. Consequently, the carbon sheet can efficiently adhere the underlying hole-transporting layer by a simple pressing technique, significantly boosting charge transfer across the interface. The TLE device achieves a champion PCE of 15.77% with an ultralow hysteresis index (HI) of 0.027, compared to the solvent-free device which has a HI of 0.176. The developed carbon-based device exhibits notably improved long-term stability when subjected to dark conditions and 40-50% RH, sustaining 82% of its initial efficiency after 24 days without encapsulation with minimal declines in J_sc and V_oc.