Design and development of a low-cost imidazole-based hole transporting material for perovskite solar cells

Low-cost and facile synthesis routes of hole-transporting materials (HTMs) are promising approaches to minimize the total cost of perovskite solar cells (PSCs) on both laboratory and commercial scales. Herein, we report 2-(3-nitrophenyl)-4,5-diphenyl-1H-imidazole (1) as a cost-effective HTM for PSCs. HTM 1 was synthesized without using any catalyst and purification process from largely available commercial precursors. HTM 1 is soluble in many organic solvents and it can be formed as a fine thin layer on top of a perovskite using a spin-coating process. In particular, density functional theory (DFT) studies showed that the energy levels of its frontier molecular orbitals are well aligned with the energy levels of the perovskite layer. Using HTM 1 in PSCs, a power conversion efficiency (PCE) of 15.20% was achieved, which was comparable to 2,2 ',7,7 '-tetrakis-(N, N-di-p-methoxyphenylamine)-9,9 '-spirobifluorene (spiro-OMeTAD, HTM 2)'s PCE of 18.21%. In this study, we revealed that HTM 1 based on simple imidazole can be explored as an alternative to spiro-OMeTAD, HTM 2, providing a way for synthesizing simple and efficient HTMs for low-cost PSCs. Low-cost and facile synthesis routes of hole-transporting materials (HTMs) are promising approaches to minimize the total cost of perovskite solar cells (PSCs) on both laboratory and commercial scales.