Polyethyleneimine-functionalized carbon nanotubes as an interlayer to bridge perovskite/carbon for all inorganic carbon-based perovskite solar cells

All inorganic perovskite solar cells (PSCs) have attracted tremendous attention because of their intrinsic structural stability, but they suffer from uncompetitive efficiency, especially the carbon electrode-based PSCs (C-PSCs), wherein the insufficient perovskite/carbon contact and interfacial recombination are of particular concern. To address these problems, we designed and fabricated a polyethyleneimine-functionalized carbon nanotube (PEI/CNT) interlayer and used it as a bifunctional bridge in all inorganic CsPbI₃ based C-PSCs. This functionalized PEI/CNT bridge connects the perovskite layer and the carbon electrode to improve the quality of the perovskite/carbon interface and also works as an interfacial passivation layer due to the coordination ability of the anchored PEI molecules on CNTs. Systematic investigations revealed that the interfacial charge transfer resistance was reduced, and surface trap states in the perovskite film were passivated. This effort led to a remarkable power conversion efficiency (PCE) of 10.55% with a high fill factor (FF) of 0.71 for the all inorganic C-PSCs. By contrast, those without the PEI/CNT bridge only attained a PCE of 7.41% and FF of 0.56. Moreover, non-encapsulated PEI/CNT based devices also showed higher stability under high humidity or high temperature conditions. Therefore, the PEI/CNT interface bridging strategy has the potential to achieve high efficiency and high stability for the all inorganic C-PSCs.