Amorphous hole-transporting layer in slot-die coated perovskite solar cells

Perovskite solar cells can be produced by a solution process and have achieved power conversion efficiency over 20% as well as improving long-term stability, offering great potential for a low cost, high efficiency photovoltaic technology. An increasing effort has been shifted to Lab-to-Fab translation, where device manufacture is accomplished by using a fully scalable printing process. One remarkable bottleneck for upscaling the device is, however, the lack of scalable hole-transport materials (HTMs) that can form the desired morphology during the printing fabrication. In this manuscript, we apply a twisted but fully π-conjugated 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl)amine-9,9′-bifluorenylidene (Bifluo-OMeTAD) into slot-die coated devices, which exhibits excellent film forming properties and outperforms the well-known Spiro-OMeTAD HTM. The improved film forming properties of Bifluo-OMeTAD are achieved via molecular design, with the chemical structure of Bifluo-OMeTAD effectively suppressing crystallization during printing. A power conversion efficiency of 14.7% is achieved in the fully slot-die coated devices based on Bifluo-OMeTAD, outperforming previous reported values for all-printed perovskite solar cells. Therefore, Bifluo-OMeTAD has attractive potential to replace Spiro-OMeTAD for the large scale roll-to-roll production of fully slot-die coated perovskite solar cells.