TiO 2 colloid-based compact layers for hybrid lead halide perovskite solar cells

Abstract In this report, we present a simple method of TiO 2 colloidal preparation and its application to form compact conformal TiO 2 (c-TiO 2 ) layers on transparent conducting substrates. The synthesized colloid has ∼5 nm particle size distribution and is stable over a period exceeding one year. The blocking nature of c-TiO 2 is evaluated by the method of cyclic voltammetry using Spiro-OMeTAD as the redox probe. This method of c-TiO 2 preparation is successfully employed in the fabrication of hybrid perovskite solar cells. The critical requirement of c-TiO 2 colloid-based compact layer as hole-blocking material is justified with the realization of photo-conversion efficiencies of 8.08% for small active areas of 0.07 cm 2 and 7.52% with relatively large active areas of 0.23 cm 2 in one-step method. In two-step sequential deposition method, a photo-conversion efficiency of 4.61% is achieved over relatively large active area of 0.64 cm 2 . Our observations suggest that c-TiO 2 formation by TiO 2 colloid can be an alternative potential route to approach for perovskite solar cell fabrication. All device processing is carried out in ambient air of relative humidity 40 ± 5% at room temperature.