Effects of crystal size and surface coverage of perovskites on electron recombination in solar cells

•Smaller sized perovskite crystals showed better performance than bigger ones.•They have drawbacks for light absorption and conductivity.•However, they form tighter surface coverage.•It is a dominant factor to suppress the electron recombination for performance. The crystal size and surface coverage of a perovskite layer at its interface with 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (sprio-MeOTAD) have been controlled by crystallization temperature (25, 40, 60 and 75 °C) during the conversion of PbI2 to MAPbI3. The high crystallization temperature induces to form large crystals and vice versa. The highest efficiency (13.9%) was observed with the perovskite layer fabricated under 25 °C among four different temperature conditions. This is mostly because of the suppressed recombination through the formation of a rather compact layer with the small sized perovskite crystals, even though its reduced light absorption and electron conductivity to a small extent. The performance has been characterized by photovoltaic parameters with help of electrochemical impedance spectroscopy (EIS) to confirm that the charge recombination is a main parameter in controlling power conversion efficiency (PCE).