  Lead halide perovskite nanocrystals (NCs) are currently emerging as one of
the most interesting solution processed semiconductors since they possess high
photoluminescence quantum yield (PLQY), and colour tunability through anion
exchange reactions or quantum confinement. Here, we show efficient solar cells
based on mixed halide (CsPbBrI2) NCs obtained via anion exchange reactions in
ambient conditions. We performed anion exchange reactions in concentrated NC
solutions with I-, thus inducing a PL red-shift up to 676 nm, and obtaining a
high PLQY in film (65%). Solar cell devices operating in the wavelength range
350-660 nm were fabricated in air with two different deposition methods. The
solar cells display a photo-conversion efficiency of 5.3% and open circuit
voltage (Voc) up to 1.31V, among the highest reported for perovskite based
solar cells with band gap below 2eV, clearly demonstrating the potential of
this material.
