Interface compatibility: how to outperform classical spiro-OMeTAD in perovskite solar cells with carbazole derivatives

The efficiency and stability of perovskite solar cells are strongly impacted by the charge extraction materials. Considering the high density of surface defects at the perovskite/charge transporting interfaces, passivation strategies should be optimized to reduce trap states at the surface of the perovskite. Herein, we investigate the concept of the interfacial layer (IL) at the perovskite/hole transport material (HTM) interface as well as the IL/HTM compatibility. A polymer IL based on poly-N-vinyl (3,6-DMPA-carbazole) (PV(Cz-DMPA)) has been used to engineer the perovskite/HTM interface in conventional perovskite solar cells. The non-conjugated PV(Cz-DMPA) polymer exhibiting suitable energy levels and high hole mobility serves as a functional IL material. Moreover, the IL also shows an efficient passivation effect. It results in lower trap state density, thus reducing interfacial charge recombination pathways. Then, two chemically compatible carbazole-based HTMs, namely Cz-P and Cz-Pyr, containing similar carbazole-based structures have been selected to strengthen IL/HTM interactions. Expectedly, a beneficial IL/HTM compatibility has been evidenced. As a result, the FF values of devices have been significantly improved (>80%), leading to high PCE (>22%) for devices fabricated with PV(Cz-DMPA)/Cz-Pyr as polymer IL/HTM materials, outperforming devices made from PV(Cz-DMPA)/spiro-OMeTAD.