An integrated organic-inorganic hole transport layer for efficient and stable perovskite solar cells

Certified power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have increased to an impressive value of 22.1%. The most efficient perovskite solar cells have the n-i-p device architecture and use 2,2',7,7'-tetrakis(N, N'-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) as the hole transport material (HTM). However, there exists microscopic inhomogeneity that is detrimental to the long-term performance of the solar cells, primarily as a result of the hygroscopicity of the lithium bis((trifluomethyl) sulfonyl) amide (LiTFSI) dopant. Here, we report a strategy for reducing heterogeneity by using an organic-inorganic integrated hole transport layer (HTL) composed of the solution-processable conjugated polymer FBT-Th4 and copper oxide (CuxO). The optimized PSCs show significant performance enhancement with power conversion efficiency up to 18.85% from a reverse voltage scan and a stabilized champion efficiency of 18.24% with negligible hysteresis. Moreover, we observe a significant enhancement of the long-term stability of perovskite solar cells under a high humidity of 70-80% in air.