A novel heterojunction layer-assisted interfacial defect control strategy for high-performance solar cells

The energy level matching of perovskites was regarded as the prerequisite for achieving high photovoltaic performance. Graphitic carbon nitride (g-C3N4) is a two-dimensional polymer semiconductor material, which has good semiconductor properties, suitable electronic band structure and excellent physical and chemical stability, and is widely used in energy and materials science fields such as for photovoltaic conversion. Graphene oxide (GO) is a two-dimensional pi-conjugated carbon atom sheet formed by sp2 hybrid bonds. Due to its unique electronic properties, g-C3N4 can be seamlessly spliced with the two-dimensional domains of GO through continuous pi-conjugated bonds, which not only effectively modifies the electronic structure of g-C3N4 but also contributes to the unhindered separation and transfer of electrons and holes in the plane. Therefore, in this work, we effectively passivated film trap defects and significantly reduced non-radiative recombination by constructing GO/g-C3N4 heterostructures as an ultra-thin interface modification layer between the perovskite layer and the electron transport layer (ETL). As a result, the addition of a GO/g-C3N4 heterojunction modification layer facilitated achieving an improved power-conversion efficiency (PCE 20.50% to 22.08%), inhibited the recombination of carriers, and improved the mobility of carriers. An unpackaged device demonstrated excellent stability, maintaining more than 90% of the initial efficiency after over 1,000 hours of storage under ambient conditions. The energy level matching of perovskites was regarded as the prerequisite for achieving high photovoltaic performance.