Defects at the interface electron transport layer and alternative counter electrode, their impact on perovskite solar cells performance

Herein, the electron transport layer and counter electrode interface, ETL-CE interface, for inverted-planar structure perovskite solar cells, and its influence on device performance was analyzed by means of scanning electron microscopy, atomic force microscopy, laser beam induced current and incident photon-to-current efficiency. The alternative CE was an eutectic alloy, Field’s metal (FM), which is easily deposited by drop casting technique without high vacuum conditions. Morphological analysis showed deficient physical contact at the ETL-FM interface, presenting many “empty spaces” within the range of few hundreds of nanometers. In contrast, an evaporated CE (Ca/Ag) used as reference (i.e. ETL-Ca/Ag interface) showed a smooth interface with good physical contact. Although the physical contact at the ETL-FM interface was deficient due to the deposition technique, the performance of the device with this alternative CE was comparable with the reference device. The best electrical parameters for cells with the alternative CE were: open circuit voltage (Voc) = 0.93 V, short circuit current density (Jsc) = 18.26 mA/cm2, fill factor (FF) = 0.62, and power conversion efficiency (PCE) = 10.50%; meanwhile for evaporated CE: Voc = 0.92 V, Jsc = 22.14 mA/cm2, FF = 0.57, and PCE = 11.60%. Therefore, the analysis of the ETL-FM interface and the achieved performance with FM suggests that the charge harvesting is good enough and that the observed defects between ETL-FM surfaces are not crucial for the performance of the devices.