Low cost triazatruxene hole transporting material for >20% efficiency perovskite solar cells

Abstract

Organic hole-transporting materials (HTM) have shown excellent ability in achieving high efficiency perovskite solar cells. However, their high cost significantly limits their applications in scaling-up perovskite solar cells. Here, we report an efficient, low-cost HTM, called TAT-^tBuSty, comprising a central triazatruxene moiety with 3 terminal tert-butoxy styrene groups and 3 hexyl side chains on the indole nitrogen. For the first time, we use an inexpensive liquid precursor to attach the donor ligand to the molecule. This enables purification of the HTM using a silica plug and recrystallization without the need for complicated column chromatography, which is typically required to purify solid-precursor-prepared HTMs. We estimate that the cost for the purified TAT-^tBuSty is $69.90 g⁻¹, which is 35% cheaper than the widely-used 2,2′7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD; ca. $112.05 g⁻¹). Using this low-cost TAT-^tBuSty as the HTM in a caesium-formamidinium mixed-cation perovskite solar cell, we have successfully achieved a champion power conversion efficiency (PCE) of 20.3% (19.4% stabilized efficiency), which is comparable to the efficiency of devices using the reference spiro-OMeTAD HTM. Our work is crucial for up-scaling of next-generation high-performance metal-halide perovskite solar cells.