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

doi:10.1021/acsami.0c17583

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

ACS Appl Mater Interfaces. 2021 Feb 17;13(6):7405-7415. doi: 10.1021/acsami.0c17583. Epub 2021 Feb 3.

Authors

Amit Sharma^{1

2}, Ranbir Singh³, Gururaj P Kini⁴, Ji Hyeon Kim¹, Mritunjaya Parashar³, Min Kim⁵, Manish Kumar⁶, Jong Seung Kim¹, Jae-Joon Lee³

Affiliations

¹ Department of Chemistry, Korea University, Seoul 02841, Republic of Korea.
² Council of Scientific & Industrial Research-Central Scientific Instruments Organisation (CSIR-CSIO), Sector 30, Chandigarh 160030, India.
³ Department of Energy & Materials Engineering, Research Center for Photoenergy, Harvesting & Conversion Technology (phct), Dongguk University, Seoul 04620, Republic of Korea.
⁴ Department of Chemical Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea.
⁵ School of Chemical Engineering, Jeonbuk National University, 567, Baekje-daero, Jeonju 54896, Republic of Korea.
⁶ Pohang Accelerator Laboratory, Pohang University of Science & Technology, Pohang 790-784, Republic of Korea.

PMID: 33534549
DOI: 10.1021/acsami.0c17583

Abstract

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-π stacking 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 (J_SC), open-circuit voltage (V_OC), 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.

Keywords: device stability; diketopyrrolopyrrole; donor−acceptor small molecules; hole-transport materials; morphology; perovskite solar cell; side-chain engineering.