Greener and Easily Available Solvent Assisted Preparation of High Efficiency Perovskite Solar Cells

To replace or reduce toxic solvents in perovskite solar cell (PSC) manufacturing, 2‐Methyltetrahydrofolate (2‐MTHF), as an important raw material for organic synthesis and an excellent solvent, is incorporated in PSCs as an additive cosoluble precursor to fabricate photolayer (FAPbI 3 ) for the first time. It is investigated that this is not only a toxicity‐reducing strategy, but also an effective defect passivation method for manufacturing PSCs. The introduction of 2‐MTHF in a stoichiometric precursor solution is capable of inducing precursor film to generate perovskite films through a simple one‐step spin‐coating process, more than 15% of toxic solvents can be reduced. The perovskite trap state is decreased by the passivated perovskite crystal surface thus improving carrier lifetime, extraction rate, and photovoltaic performance. The maximum PCE of the solar cell when the 2‐MTHF volume fraction is optimized at 15% is improved to 23.58%, up from 7% in the control. Meanwhile, the notorious J–V hysteresis is much suppressed. Hence, it is expected that novel 2‐MTHF will find applications in PSCs and optoelectronic devices.