New interfacial materials for rapid hole-extraction in organic photovoltaic cells

Abstract

Two new hole-extraction materials, TPDI (5,10,15-triphenyl-5H-diindolo[3,2-a:3′,2′-c]carbazole) and TBDI (5,10,15-tribenzyl-5H-diindolo[3,2-a:3′,2′-c]carbazole), were synthesized and explored in planar heterojunction organic solar cells (OSCs). The synthesized materials have good transparency in the visible spectrum, high hole mobility, and compatible highest occupied molecular orbital (HOMO) values with the donor material, which make them excellent hole-extraction layers (HELs) for OSCs. The SubPc (subphthalocyanine chloride)/C₆₀ and SubNc (subnaphthalocyanine chloride)/C₆₀ OSCs with a TBDI HEL show impressive 35.9% and 29.1% improvements in power conversion efficiencies compared to reference devices. Their HOMO values were evaluated as 5.2–5.3 eV and hole mobilities were measured as 5.9–6.1 × 10⁻³ cm² V⁻¹ s⁻¹ at 0.3 MV cm⁻¹ by the space-charge limited current method.