Mechanical Compression‐Enabled Carbon‐Based Perovskite Solar Cells with Enhanced Efficiency and Stability

Carbon electrode‐based perovskite solar cells (C‐PSCs) without hole transport layer (HTL) have been emerging as a promising low‐cost photovoltaic technology with excellent stability for commercialization. However, the loose physical contact between the carbon electrode and perovskite layer, as well as the relatively poor conductivity of the carbon film, contributes mainly to the large gap in the power conversion efficiency (PCE) between C‐PSCs and the metal (Ag, Au, etc.,) electrode‐based counterparts. To this end, a simple but effective mechanical compression strategy for efficient C‐PSCs is developed. The mechanical compression densifies the porous carbon electrode for high film conductivity and also provides intimate contact between carbon and perovskite layers for fast charge extraction. Consequently, the resulting HTL‐free C‐PSCs using MAPbI 3 (MA = methylammonium) absorber yield a PCE of 15.29%, corresponding to a 27.6% improvement compared to the counterpart without mechanical pressing treatment. Moreover, the compacted carbon film also serves as an enhanced barrier against the intrusion of water and oxygen, and the unencapsulated device retains 88.9% of its initial PCE after 1000 h of aging in ambient conditions with 35 ± 2% humidity. This work paves a simple and effective way toward efficient and stable C‐PSC.