Poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine, also known as polyTPD, is an excellent hole transport layer material used in photovoltaics such as perovskite solar cells. It has also proven polyTPD is a promising candidate HTL in multilayer WPLEDs because its HOMO level 5.2 eV is very close to the work function of the indium tin oxide ITO/PEDOT:PSS anode.
