Investigations of Carrier Transport Mechanisms in Perovskite Solar Cells with Different Types of ZnO Layer

The interfacial mechanisms of carrier transport in perovskite solar cells with different types of zinc oxide (hydrothermal solution method (ZnO_HT) and sol–gel method (ZnO_SG)) are investigated. Power conversion efficiencies of the devices with ZnO_HT and ZnO_SG layers are 18.66% and 13.39%, respectively, which are significantly varied by the rates of photoelectron injection and electron–hole recombination. The space-charge-limited current and electrochemical impedance measurements both show that the device utilizing ZnO_HT layer exhibits fewer internal defects compared to that with ZnO_SG layer. Via transient absorption spectroscopy, faster injection of photoelectrons from the active layer to the transport layer occurs at ≈3.8 ps in the devices with ZnO_HT layer, which is half of the value observed in devices with ZnO_SG layer and benefits the device performance. Moreover, a faster electron–hole recombination in devices with ZnO_SG degrades device performance due to the trap states in high-defect-density devices. Both device performances stably maintain a level higher than 98% of the initial value after over 600 h without encapsulation in glove box. Finally, the structural and electronic properties of charge transport layer can be controlled by the methods of preparation and ZnO_HT shows great promise in enhancing perovskite solar cell efficiency with relatively low-temperature process.