Boron and phosphorus co-doped carbon counter electrode for efficient hole-conductor-free perovskite solar cell

Chemical doping is adopted to tune the work function and electrical conductivity of carbon counter electrode (CE) in HTM-free organometallic halide perovskite solar cells (PSCs). In this work, the boron and phosphorus co-doped carbon (BPC) CE is constructed by coating a B doped carbon layer onto the P-doped carbon (PC). The work function of BPC CE with B/P co-doping (B: 2.68   at.%, P: 2.23   at.%) is thus regulated to 5.12   eV from the 5.01   eV of pure carbon and 4.81   eV of PC, and the sheet resistance is modulated to 8.41   Ω   sq −1 from 14.75   Ω   sq −1 of pure carbon and 7.89   Ω   sq −1 of PC. As a consequence, the BPC-based PSCs deliver a power conversion efficiency of 6.78%, higher than those of pristine carbon (3.72%), PC (5.39%) and BC (5.20%) based PSCs, and even comparable to that of conventional Au-based device (7.22%), due to the enhanced hole extraction ability and the maintained high electronic conductivity. Moreover, the good stability in ambient condition over a period of 720   h is also demonstrated in the BPC-based PSCs. The successful application of BPC CE in PSCs shows a promising way for fabricating low-cost, large-scale and highly efficient PSCs in future.