Synthesis Of Truxene-based Dopant-Free HTMs And Application In Inverted Planar Perovskite Solar Cells

Solar power is the world's most abundant energy resource,and it's clean.The difficulty has always been converting solar energy in an efficient and cost-effective way.With the discovery of the photoelectric effect,photovoltaic cells are the most promising avenue,directly converting the photons to electricity.The rapid developing perovskite solar cells?PSCs?have been demonstrated to potentially meet the requirements of commercialization.The hole transport material is an important component of PSCs,affecting device efficiency and stability.The development of dopant-free HTMs is a research hotspot for perovskite solar cells?PSCs?,because commonly used dopants deteriorate the device stability.So far,only a few of dopant free organic small HTMs have been explored for the inverted PSCs,requiring in-depth and systematic investigation.In this work,four new truxene-based HTMs?M115-118?,with different alkyl chains and periphery arylamine have been deliberately synthesized and applicated in the inverted PSCs.The impact that the length of alkyl and periphery arylamine has on the photophysical,electrochemical and hole transporting properties has been systematically investigated.These new HTMs exhibit decent hole mobility of 10^-33 cm² V^-11 s^-1,which ensure efficient hole extraction in dopant-free devices.The hexyl chain imparts higher hole mobility to the hole transporting material,and optimizes the morphology of the hole transporting layer,so that the M116-based device obtains a higher open circuit voltage and a filling factor;the arylamine conjugated structure affects the glass transition temperature,also intramolecular charge transport and energy level distribution,allowing the M118-based device to achieve higher fill factor and open circuit voltage.PSCs using the dopant-free M118 exhibit a champion power conversion efficiency of over 17%,much higher than the value of 14.4%achieved using PEDOT:PSS.Importantly,PSCs based on these truxene HTMs exhibit significantly enhanced durability under UV light compared with PEDOT:PSS.This work not only provides efficient dopant-free HTMs,but also reveals that the adjustment of length of alkyl as well as periphery arylamine is necessary for development of stable and efficient truxene HTMs.