Efficient and stable perovskite large area cells by low-cost fluorene-xantene-based hole transporting layer

Among the new generation photovoltaics, perovskite solar cell (PSC) technology reached top efficiencies in a few years. Currently, the main objective to further develop PSCs is related to the fabrication of stable devices with cost-effective materials and reliable fabrication processes to achieve a possible industrialization pathway. In the n-i-p device configuration, the hole transporting material (HTM) used most is the highly doped organic spiro-fluorene-based material (Spiro-OMeTAD). In addition to the high cost related to its complex synthesis, this material has different issues such as poor photo, thermal and moisture stability. Here, we test on small and large area PSCs a commercially available HTM (X55, Dyenamo) with a new core made by low-cost fluorene-xantene units. The one-pot synthesis of this compound reduces 30 times its cost with respect to Spiro-OMeTAD. The optoelectronic performances and properties are characterized through JV measurement, IPCE (incident photon to current efficiency), steady-state photoluminescence and ISOS stability test. SEM (scanning electron microscope) images reveal a uniform and pinhole free coverage of the X55 HTM surface, which reduces the charge recombination losses and improves the device performance relative to Spiro-OMeTAD from 16% to 17%. The ISOS-D-1 stability test on large area cells without any encapsulation reports an efficiency drop of about 15% after 1000 h compared to 30% for the reference case.