Depth-Dependent Post-Treatment for Reducing Voltage Loss in Printable Mesoscopic Perovskite Solar Cells

The printable mesoscopic perovskite solar cells consisting of a double layer of metal oxides covered by a porous carbon film have attracted attention due to their industrialization advantages. However, the tens-of-micrometer thickness of the triple scaffold leads to a challenge for perovskite to crystallize and for the charge carriers to separate and travel to the electrode, which limits the open circuit voltage (V_OC ) of such devices. In this work, a depth-dependent post-treatment strategy is demonstrated to synergistically passivate defects and tune interfacial energy band alignment. Two thiophene derivatives, namely 3-chlorothiophene (3-CT) and 3-thiophene ethylenediamine (3-TEA), are selected for the post-treatment. Energy-dispersive X-ray spectroscopy proves that 3-CT is uniformly distributed throughout the triple scaffold and effectively passivates the defects of the bulky perovskite, while 3-TEA reacts rapidly with the loose perovskite in the carbon layer to form 2D perovskite, forming a type II energy band alignment at the perovskite/carbon interface. As a result, the defect-assisted recombination is suppressed and the interfacial energy band is regulated, increasing the V_OC to 1012 mV. The PCE of the devices is enhanced from 16.26% to 18.49%. This depth-dependent post-treatment strategy takes advantage of the unique structure and provides a new insight for reducing the voltage loss.