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DOI: 10.1002/admi.201800209 exceeding 20%[2–4] in perovskite (PVSK)based photovoltaics. These superlative metrics can be attributed to the favorable characteristics of hybrid PVSKs as light harvesting media, including broadband absorption, high electron and hole mobilities, when compared to typical values in organic semiconductors, and long charge carrier lifetimes.[5,6] Furthermore, PVSKs can be prepared using solution-based, lowtemperature techniques that allow for considerable flexibility.[7–10] The characteristics that have brought cost-effective and high-efficiency solar cells closer to reality also lend themselves to a variety of other applications, such as in tunable lasers, light-emitting diodes, and photodetectors.[8,11,12] In all of these, efficient performance is strongly dependent on the optimal interaction at the interfaces between the active PVSK film and the extraneous layers implemented for charge dissociation, extraction, and conveyance. The properties of the electron and hole transport layers (ETL and HTL, respectively) therefore play critical roles in the device design.[13] Various ETL materials have been incorporated in PVSK solar cells,[13–20] and among these, ZnO has proven superior in several respects as an ETL. For example, its electron mobility is in the range of 200–300 cm2 V−1 s−1, significantly higher than that of TiO2, and additionally, there have been indications of its contribution to improving long-term operational stability[20] of PVSK devices. Aside from thin films and epi-layers, metal oxide nanostructures have also been incorporated as ETLs in solar cells as a means of increasing absorption cross section without adding to the physical size of the device. Nanowires and nanorods of TiO2, Y:TiO2, ZnO, and WO3 have been implemented in PVSK solar cells as ETLs with promising results, and again, ZnO is an attractive candidate here too, as ZnO nanostructures can be grown at relatively low temperatures.[18,23,24] Thus far, the research effort on investigating heterostructures comprising PVSK films and ZnO layers has been focused primarily on photovoltaic characterization. This has necessarily limited the perspective to optimization of power conversion efficiency alone, without systematically studying the fundamental processes occurring at the interface. A detailed and thorough understanding of the interaction between the two The authors explore the potential of ZnO layers of different morphologies, including single crystalline, micro-structured, and nano-structured substrates, for tuning exciton binding energy and influencing charge extraction when interfaced with pure (CH3NH3PbI3) and mixed (CH3NH3PbI3−xClx) halide hybrid perovskite (PVSK) thin films. Electron microscopy characterization of the PVSK/ZnO interfaces are correlated with charge transfer properties, probed by means of temperature, power, and time-resolved photoluminescence (PL) spectroscopy. The results show that at room temperature, the single crystalline ZnO film promotes PL quenching, and reduces recombination lifetime along with exciton density in the PVSK films, all indicative of efficient electron extraction. Nevertheless, the micro-structured ZnO layers exhibit a mild increase of the PVSK PL at room temperature, and the nano-structured ZnO enhances PL by up to several thousand-fold, while simultaneously enhancing recombination rates by 50%. These trends are temperature dependent, and the findings highlight two opposing aspects of how excitonic dissociation in PVSK thin films is affected by the morphology of the underlying ZnO layers. While the single crystalline ZnO can be leveraged as an efficient electron extraction layer for application in photovoltaic devices, the microand nano-structured ones offer potential new opportunities for utilization of high quantum yield hybrid perovskites in opto-electronic platforms.