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

Abstract

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).