Side-Chain Engineering of Diketopyrrolopyrrole-Based Hole-Transport Materials to Realize High-Efficiency Perovskite Solar Cells

Amit Sharma, Ranbir Singh, Gururaj P. Kini, Ji Hyeon Kim, Mritunjaya Parashar, Min Kim, Manish Kumar, Jong Seung Kim, Jae Joon Lee

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


The design and synthesis of a stable and efficient hole-transport material (HTM) for perovskite solar cells (PSCs) are one of the most demanding research areas. At present, 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-MeOTAD) is a commonly used HTM in the fabrication of high-efficiency PSCs; however, its complicated synthesis, addition of a dopant in order to realize the best efficiency, and high cost are major challenges for the further development of PSCs. Herein, various diketopyrrolopyrrole-based small molecules were synthesized with the same backbone but distinct alkyl side-chain substituents (i.e., 2-ethylhexyl-, n-hexyl-, ((methoxyethoxy)ethoxy)ethyl-, and (2-((2-methoxyethoxy)ethoxy)ethyl)acetamide, designated as D-1, D-2, D-3, and D-4, respectively) as HTMs. The variation in the alkyl chain has shown obvious effects on the optical and electrochemical properties as well as on the molecular packing and film-forming ability. Consequently, the power conversion efficiency (PCE) of the PSC under one sun illumination (100 mW cm-2) is shown to increase in the order of D-1 (8.32%) < D-2 (11.12%) < D-3 (12.05%) < D-4 (17.64%). Various characterization techniques reveal that the superior performance of D-4 can be ascribed to the well-aligned highest occupied molecular orbital energy level with the counter electrode, the more compact π-πstacking with a higher coherence length, and the excellent hole mobility of 1.09 × 10-3 cm2 V-1 s-1, thus providing excellent energetics for effective charge transport with minimal charge-carrier recombination. Furthermore, the addition of the dopant Li-TFSI in D-4 is shown to deliver a remarkable PCE of 20.19%, along with a short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) of 22.94 mA cm-2, 1.14 V, and 73.87%, respectively, and superior stability compared to that of other HTMs. These results demonstrate the effectiveness of side-chain engineering for tailoring the properties of HTMs, thus offering new design tactics to fabricate for the synthesis of highly efficient and stable HTMs for PSCs.

Original languageEnglish
Pages (from-to)7405-7415
Number of pages11
JournalACS Applied Materials and Interfaces
Issue number6
Publication statusPublished - 2021 Feb 17


  • device stability
  • diketopyrrolopyrrole
  • donor-acceptor small molecules
  • hole-transport materials
  • morphology
  • perovskite solar cell
  • side-chain engineering

ASJC Scopus subject areas

  • Materials Science(all)


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