Influence of Structure and Morphology of Perovskite Films on the Performance of Perovskite Solar Cells

Abstract

Perovskite solar cells based on the inorganic/organic hybrid perovskite have attracted increasing attention over the past 3 years. Many studies have been done in this area. Controling the morphology of the perovskite film is an effective way to improve the photoelectric conversion efficiency of the devices. In our reserch, we studied the influence of structure and morphology of perovskite films on the performance of the organic-inorganic hybrid perovskite solar cells which prepared by a sequential deposition method. Mesoporous TiO2 scaffold were introduced as electron collecting layer. Lead iodide (PbI2) was then spin cast on the TiO2 scaffold. The PbI2 subsequently transformed into the perovskite (CH3NH3PbI3) by dipping the TiO2/PbI2 film into a solution of CH3NH3I. We studied the difference between the PbI2 film with or without drying under room temperature after spin-coating. Through drying under room temperature, larger pores formed in the PbI2 film. While without drying under room temperature, smaller and shallower pores formed in the PbI2 film. The results show that larger pores in PbI2 film leads to more complete transformation of PbI2 to CH3NH3PbI3 and larger CH3NH3PbI3 particles. CH3NH3PbI3 films were prepared with three different processes: (a) direct dipping the PbI2 film with smaller pores into the CH3NH3I solution; (b) direct dipping the PbI2 with larger pores into the CH3NH3I solution; (c) dipping the PbI2 with larger pores into the CH3NH3I solution after pre-wetting.The resulting CH3NH3PbI3 films were studied with SEM, UV-vis absorption spectrum and XRD. The particles size of the CH3NH3PbI3 are 150, 250 and 350 nm for process (a), (b) and (c) respectively. CH3NH3PbI3 films fabricated through process (a) show insufficient absorption due to the insufficient transformation of the PbI2. The pre-wetting procedure leads to slower reaction result in larger CH3NH3PbI3 particle size. Devices with proper size of CH3NH3PbI3 particles show the highest photoelectric conversion efficiency. An efficiency of 13.5% was achieved with a Jsc of 17.8 mA/cm, a Voc of 1.05 V and a FF of 72.5%.