Design of B,N Co‐Doped Carbon Spheres for Highly Effective Back Interface Engineering in Planar Carbon‐Based Perovskite Solar Cells

Carbon‐based perovskite solar cells (C‐PSCs) are inexpensive and stable, demonstrating great potential for commercial applications. However, the relatively low power conversion efficiency (PCE) stemmed from the poor conductivity of carbon electrodes and the energy level mismatch of the perovskite/carbon back interface are the key obstacles to further development of C‐PSCs. In this work, the electronic properties of a carbon electrode are regulated by designing a novel kind of B and N co‐doped carbon sphere (BN‐CS), resulting in a downshift of the Fermi level, which can minimize the energy level mismatch of the back interface. The optimized energy level alignment of the back interface accelerates the carrier separation, extraction, and transportation processes while effectively inhibiting charge recombination. Consequently, combined with an efficient buried passivation using aminomethylphosphonic acid, the PCE of the C‐PSCs is finally enhanced to 18.56%, much higher than that (15.16%) of the pristine C‐PSCs without any modification. Furthermore, the stability of the C‐PSCs is also enhanced using the synthesized BN‐CS with excellent hydrophobicity, and the PCE retention rate is up to 98.2% for the 30‐day stability test.