Nickel Oxide/Cobalt Phthalocyanine as a Hole Transport Bilayer for Efficient and Stable Inverted Perovskite Solar Cells

Abstract

This study demonstrates that the use of bilayer films based on nickel oxide (NiOx;) and cobalt phthalocyanine (CoPc) represents a promising hole transport layer (HTLs) for inverted perovskite solar cells (PSCs). NiOx; films are fabricated using the spin-coating method from a sol–gel solution. Films (CoPcevap) and nanowires (CoPcnws) on the NiOx; surface are produced by thermal sputtering and physical gradient-temperature vapor deposition. It is demonstrated that PSCs with a NiOx; layer exhibit a power conversion efficiency (PCE) of only 18,1%. The incorporation of a CoPcevap intermediate layer between NiOx; and the perovskite increases the PCE to 19.1%. The highest PCE, reaching 20.7%, is achieved with a bilayer HTLs based on NiOx;/CoPcnws. Analysis of the PSC impedance spectra shows that the CoPcnws intermediate layer reduces the HTLs resistance and increases the recombination resistance at the perovskite/HTLs interface, which extends the effective lifetime of charge carriers. The stability of NiOx;-based PSCs is 48%, while PSCs with bilayer HTLs based on NiOx;/CoPcnws and NiOx;/CoPcevap exhibits higher stability of 71% and 90% over 600 hours. The results demonstrated that solar cells based on NiOx;/CoPc inhibit the perovskite degradation process and reduce charge recombination, thereby improving the performance and stability of the inverted PSCs.