Work Function Tuning of Carbon Electrode to Boost the Charge Extraction in Hole Transport Layer‐Free Perovskite Solar Cells

Abstract Perovskite solar cell (PSC) is a promising photovoltaic technology that achieves over 26% power conversion efficiency (PCE). However, the high materials costs, complicated fabrication process, as well as poor long‐term stability, are stumbling blocks for the commercialization of the PSCs in normal structures. The hole transport layer (HTL)‐free carbon‐based PSCs (C‐PSCs) are expected to overcome these challenges. However, C‐PSCs have suffered from relatively low PCE due to severe energy loss at the perovskite/carbon interface. Herein, the study proposes to boost the hole extraction capability of carbon electrode by incorporating functional manganese (II III) oxide (Mn 3 O 4 ). It is found that the work function ( W F ) of the carbon electrode can be finely tuned with different amounts of Mn 3 O 4 addition, thus the interfacial charge transfer efficiency can be maximized. Besides, the mechanical properties of carbon electrode can also be strengthened. Finally, a PCE of 19.03% is achieved. Moreover, the device retains 90% of its initial PCE after 2000 h of storage. This study offers a feasible strategy for fabricating efficient paintable HTL‐free C‐PSCs.