Indolocarbazole-core linked triphenylamine as an interfacial passivation layer for perovskite solar cells

Abstract

We herein design and synthesize two small organic molecules with hole transport properties, 4,4′-(5,11-dioctyl-5,11-dihydroindolo[3,2-b]carbazole-6,12-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TM5) and 4,4′-(5,11-dioctyl-5,11-dihydroindolo[3,2-b]carbazole-6,12-diyl)bis(N,N-bis(4-(methylthio)phenyl)aniline) (TM6), as interfacial layers between the perovskite and hole transport layer (HTL) in perovskite solar cells (PSCs). There exist coordination interactions and hydrogen bonds between the TM molecules and perovskite, as revealed by X-ray photoelectron and infrared spectroscopy. For this reason, after the perovskite film is coated with the TM5 and TM6 layers, respectively, the defect density is reduced significantly from 2.78 × 10¹⁵ to 6.49 × 10¹⁴ and 4.99 × 10¹⁴ cm⁻³. In addition, a gradient energy level alignment is formed between the perovskite, interface layer, and HTL. As a consequence, hole extraction is significantly enhanced and charge recombination is notably slowed down. The TM5 and TM6 interfacial layers thus bring about significant enhancements of power conversion efficiency (PCE) from 17.42% to 19.53% and 20.18%, respectively. The TM coatings can also protect perovskite against humidity. The TM5 and TM6 coated PSCs demonstrate good stability after 1056 h aging at a relative humidity of 30–40% with decreases of PCE only by 5% and 3%, respectively, in contrast to the 43% decline of PCE for the control solar cell.