Band Alignment Strategy for Printable Triple Mesoscopic Perovskite Solar Cells with Enhanced Photovoltage

Printable triple mesoscopic structures for organic-inorganic hybrid perovskite solar cells (PSCs) have recently obtained significant attention, and they possess a superior long-term stability in comparison to those of planar structured PSCs. In comparison with planar structures, however, triple mesoscopic structures typically show lower open-circuit voltages (V-oc). Evidence suggests that nonradiative recombination governed by the mismatched energy levels between the perovskite film and the electron-transporting layer (or hole-transporting layer) is the main cause for photovoltage losses. Here we introduced a gradient bilayered zinc tin oxide (ZTO) ETL for fully printed mesoporous PSCs. This approach reduces the energy loss and augments the V-oc, which benefits from the suitable matching of cascade level between the perovskite and the ZTO ETL. By tuning of the Zn content, ZTO films with gradient energy levels and different carrier concentrations are acquired. Our optimized device delivers a high V-oc of 1.02 V and PCE of 15.86%. These findings provide a simple pathway to design the interface between ETL and perovskite and to tailor the band alignment to suppress interfacial trap-assisted recombination of fully printed mesoporous PSCs for enhancing V-oc and charge extraction simultaneously.