Tin–Lead Perovskite Solar Cells Fabricated on Hole Selective Monolayers

According to the detailed balanced limit for a single-junction solar cell, tin–lead (Sn–Pb) perovskite solar cells (PSCs) can achieve power conversion efficiencies (PCEs) more than Pb-PSCs. However, the rise in PCE of Sn–Pb PSCs is limited by the choice of hole transport layer to PEDOT:PSS only. Inspired by the use of hole selective monolayers (HSM) in Pb only PSCs, here, we employed 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz), leading to PCE (21.39%) comparable to PSCs fabricated on conventional PEDOT:PSS (21.37%). Moreover, we reported a small molecule, methyl phosphonic acid (MPA), employing which an equipotential performance (PCE= 21.08%) was obtained owing to its passivation effect on the transparent conducting oxide (TCO) layer. Furthermore, by taking motivation from the idea of cosensitization in dye sensitized solar cells, we explored the point that the coabsorption of 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz) and a small molecule MPA on TCO glass led to the Sn–Pb PSC (1.25 eV) with a PCE of 23.3% and open-circuit voltage of 0.88 V.