Phenothiazine Functionalized Multifunctional A−π–D−π–D−π–A-Type Hole-Transporting Materials via Sequential C–H Arylation Approach for Efficient and Stable Perovskite Solar Cells

Abstract

Three phenothiazine-based A−π−D−π−D−π−A-type small molecules containing various terminal acceptor units, which act as Lewis base blocks, have been synthesized via an efficient and stepeconomical, direct C−H arylation strategy in the aim toward the development of hole-transporting materials (HTMs) with multifunctional features (such as efficient hole extraction layer, trap passivation layer, and hydrophobic protective layer) for perovskite solar cells (PrSCs). Optical-electrochemical correlation and density functional theory studies reveal that dicyanovinylene acceptor in SGT-421 downshifted the highest occupied molecular orbital (HOMO) level (−5.41 eV), which is more proximal to the valence band (−5.43 eV) of the perovskite, whereas N-methyl rhodanine in SGT-420 and 1,3indanedione (IND) in SGT-422 destabilized the HOMO, leading to an increased interfacial energy-level offset. SGT-421 exhibits superior properties in terms of a sufficiently low-lying HOMO level and favorable energy-level alignment, intrinsic hole mobility, interfacial hole transfer, hydrophobicity, and trap passivation ability over spiro-OMeTAD as a benchmark small-molecule HTM. As envisaged in the design concept, SGT-421-based PrSC not only yields a comparable efficiency of 17.3% to the state-of-art of spiro-OMeTAD (18%), but also demonstrates the enhanced long-term stability compared to the spiro-OMeTAD because of its multifunctional features. More importantly, the synthetic cost of SGT-421 is estimated to be 2.15 times lower than that of spiro-OMeTAD. The proposed design strategy and the study of acceptor−property relationship of HTMs would provide valuable insights into and guidelines for the development of new low-cost and efficient multifunctional HTMs toward the realization of efficient and long-term stable PrSCs.

D–π–A‐Type Triazatruxene‐Based Dopant‐Free Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells

“…Inspired by these results, we have made use of the Lewis base functional blocks in the HTM structure to create a cost‐effective solution for optimizing the performance of the device without the need of adding an extra passivation layer. [ 30 ] Herein, we have developed three novel D–π–A‐type molecules to deeper investigate the design strategy of dopant‐free HTM. A planar TAT central core (D), alkylated terthiophenes as conjugated arms (π), and various strong electron acceptor units (A) are introduced into the molecules.…”

Stable Perovskite Solar Cells Using Molecularly Engineered Functionalized Oligothiophenes as Low‐Cost Hole‐Transporting Materials

“…structure, precise molecular weight, and reliable batch-tobatch reproducibility. [15][16][17][18] To date, 2,2,7,7-tetrakis(N,N-dip-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD) has been widely used as the benchmark HTM in PSC devices. [19] Unfortunately, the complicated synthesis and tedious purification of spiro-cored HTMs make it expensive.…”

Structure-induced optoelectronic properties of phenothiazine-based materials

“…12) to create a material that embodies all the most important features of an HTM, such as good hole extraction, stability, hydrophobicity, and trappassivation ability. 74 The chemical configuration consists of A-p-D-p-D-p-A architecture backbone end-capped with three different acceptors (Lewis base blocks) on both sides for hole extraction and the passivation of undercoordinated Pb ions. The donor units are PTZ and they can lower the HOMO level, besides having good hole transport and thermal stability and less propensity for aggregation because of their non-planar and butterfly-shaped structure.…”