Interface studies of the planar heterojunction perovskite solar cells

Planar perovskite solar cells (PSCs) with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have attracted much interest because they can be fabricated by low temperature process and exhibit high power conversion efficiency (PCE). The PCE is strongly dependent on the interface properties between the PCBM layer and cathode. In this work, solution-processable material, rhodamine 101, was used as the interfacial layer between the PCBM layer and Ag cathode. These interfacial materials significantly increase the fill factor so as to the PCE of the PSCs. The optimal power conversion efficiencies are 13.2% (CH3NH3PbI3) and 14.8% (CH3NH3PbI3−xClx) for the devices with rhodamine 101 as the electron collection interlayer, saliently higher than that (8.5% and 12.0%) of control devices without an electron-collection interlayer. The effect of the interfacial material is carefully examined by time-resolved photoluminance spectroscopy (TR-PL), ultraviolet photoelectron spectroscopy (UPS), and kelvin probe force microscopy (KPFM) techniques. Decreased work-function and energy barrier, enhanced electron extraction and prolonged free carrier lifetime all contributed to the photovoltaic performance improvement.