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

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 .