Organic Salt-Doped Polymer Alloy: A New Prototype Hole Transporter for High-Photovoltaic-Performance Perovskite Solar Cells

Hole-transporting layer (HTL) is one of the key components in a regular perovskite solar cell (r-PSC), which has the function of extracting the photon-excited holes from the absorber and then transporting them to the electrode. The most commonly used HTL in r-PSC is LiTFSI and tBP-doped spiro-OMeTAD. The inevitable instability induced by a deliquescent inorganic salt (LiTFSI), the migration of small lithium ions, and the necessary oxidation process in air hinder the commercialization of this technology. In this paper, a new undoped D-A copolymer <b>(P15)</b> is used as a hole-transporting material (HTM) for r-PSC but with moderate photovoltaic performance. Therefore, an organic salt, DPI-TPFB, having a big organic cation and a hydrophobic anion, was used as a dopant to increase the conductivity/hole mobility of <b>P15</b> while avoiding the instability caused by lithium salt and moisture. Furthermore, an amphiphilic polymer, PDTON (with hole- transporting and perovskite-passivation ability), was added to <b>P15</b> to form a polymer alloy, (<b>P15</b> + PDTON), to further enhance the crystallinity and, therefore, the conductivity/hole mobility of <b>P15</b> via space-confined interaction. As a result, r-PSCs based on DPI-TPFB-doped (<b>P15</b> + PDTON) HTLs exhibit the highest power conversion efficiency (PCE) of 18.8%, which is higher than those of the cells based on DPI-TPFB-doped <b>P15</b> (15.08%), DPI-TPFB-doped PDTON (7.37%), and undoped (<b>P15</b> + PDTON) (15.66%) HTLs. Cells based on DPI-TPFB-doped (<b>P15</b> + PDTON) HTL also have much better long-term stability than those using LiTFSI and tBP-doped spiro-OMeTAD as an HTL. The studies show that a polymer-compatible organic salt, DPI-TPFB, can be used as a stable dopant to increase the hole mobility of polymeric HTL without sacrificing the stability of the resulting cells, and mixing two ordinary photovoltaic performance polymeric HTLs (such as <b>P15</b> and PDTON) can form a high- photovoltaic-performance polymer alloy (<b>P15</b> + PDTON) HTL. Therefore, organic salt-doped polymer alloy can be regarded as a new prototype hole transporter for high-photovoltaic- performance PSCs.