Green solvent-based approaches to the synthesis and processing of metalorganic hole-transport materials for perovskite solar cells

Phthalocyannines are versatile molecules used in many technologies such as photonics and photovoltaics. Spiro-OMeTAD is popularly employed as HTL in conventional n-i-p architecture perovskite solar cells (PSCs) for delivering promising efficiencies in the devices. However, the tedious manufacturing/ synthesis procedure followed by rigorous purification makes it an HTL for big budgets. Also, spiro-OMeTAD and similar molecules are solution-processed exclusively in chlorinated solvents- CB and dichlorobenzene (DCB) or toluene. Thus, the solvent for processing is one of the many reasons to be addressed for going green in PSC fabrication. This work is mainly focused on the established macrocyclic hole transport materials, such as tetra-tert-butyl phthalocyanines and replacing the conventionally used solvents with greener alternatives to make the devices more sustainable and possibly cost-effective. We have chosen glycerol-anisole mixtures to synthesize three state-of-the-art tert-butyl phthalocyanines Zn, Cu, Co (TBU4-Cu, TBU4-Zn, TBU4-Co) materials which are investigated as HTLs for planar n-i-p perovskite solar cells and green solvent anisole as deposition solvents. HTLs fabricated with anisole show PCEs of TBU4-Zn, Co, Cu 9.57%, 7.53%, 9.97% respectively and HTLs with CB show PCEs of TBU4-Zn, Co, Cu 8.40%, 7.56%, 6.75% respectively. So switching to anisole from CB doesn't alter PCEs significantly.