Highly efficient and stable ZnO-based MA-free perovskite solar cells via overcoming interfacial mismatch and deprotonation reaction

Zinc oxide (ZnO) is expected to be the desirable electron transport layer (ETL) for planar perovskite solar cells (PVSCs) because of excellent electron mobility, superior transmittance in the visible spectrum and aligned energy level with perovskite. However, the development of ZnO-based PVSCs is relatively stagnant, mainly due to interfacial mismatch and deprotonation. Herein, aluminium-doped ZnO modified by polydopamine (AZO:PDA) as ETL has firstly been found to optimize interfacial contact and inhibit detrimental interfacial reaction. The surface defects of AZO:PDA has been effectively passivated to mitigate the non-radiative carriers recombination. Moreover, various functional hydroxyl and amino groups from AZO:PDA can not only induce the vertical growth of perovskite grains, but also release the lattice strain and inhibit the deprotonation reaction. Consequently, the rigid device (ITO/AZO:PDA/FA0.9Cs0.1PbI3/Spiro-OMeTAD/Ag) shows a champion power conversion efficiency (PCE) of 21.36% with small hysteresis effect. The unencapsulated devices can preserve 90% and 88% of their initial efficiencies after storing at 85 °C for 360 h and continuous light for 500 h, respectively. In addition, a PCE of 18.51% is achieved in flexible device due to the advantages of bendability and interfacial adhesion from AZO:PDA, which is one of the highest PCEs recorded among ZnO-based flexible PVSCs.