Preparation And Properties Of Thickness-insensitive Electron Transport Layer Based On Non-conjugated Polymers

Polymer solar cells(PSCs)have attracted wide attention in academic and industrial researchers due to their advantages of solution processing and large-area flexible devices manufacturing in the last decade.Interface engineering is one of the key factors to ensure the maximum efficiency and stability of PSCs.Among of them,low-cost,low-temperature solution processing and thickness-insensitive electron transport layers(ETLs)have been exploited in order to apply to future application by Roll-to-Roll process to prepare large area flexible devices.Therefore,a series of new non-conjugated polymers have been designed and prepared for thickness-insensitive electron transport layer to prepare high performance PSCs.1.Two non-conjugated polymers,named as PEIE-DIO and PEIE-IB,have been designed and synthesized by quaterisation reaction between polyethyleneimine ethoxylated(PEIE)and 1,8-diiodooctane(DIO)or n-iodobutane(IB)respectively.The results of X-ray photoelectron spectroscopy,infrared spectroscopy and Malvin potential particle size analysis results indicate that quaternary ammonium iodides exist in PEIE-DIO and PEIE-IB,and PEIE-DIO is transformed into a low cross-linking polymer.The results show that PEIE-IB with quaternary ammonium iodide possesses higher conductivity and electron mobility than PEIE,indicating that the quaternary ammonium structure is beneficial to improving the electronic transport property of the polymer.What's more,PEIE-DIO with quaternary ammonium salt and cross-linked structure has higher conductivity and electron mobility than PEIE-IB,which indicates that the cross-linked structure is in favor of forming three-dimensional conductive network structure and improving electronic transport property of polymer.The inverted PSCs have been prepared using these polymers as electron transport layers and PTB7-Th:PC71BM blend film as the photoactive layer.Among them,the PSCs based on PEIE-DIO as the ETL show the best photovoltaic performance.The PSC shows a power conversion efficiency(PCE)of 10.06%when the thickness of PEIE-DIO is 9 nm,and it still keep a high PCE of 8.88%at the thickness of 50 nm.It is the first case that the polymer without any conjugated units has been used as thick ETLs to prepare high performance PSCs.2.In order to investigate the effect of halogen anions on the electron transport property of the non-conjugated polymers with three dimensional conductive network structure,the polymers PEIE-DIO,PEIE-DBO and PEIE-DCO have been designed and prepared by quaterisation reaction between PEIE and equivalent DIO,1,8-dibromooctane(DBO)and 1,8-dichlorooctane(DCO)respectively.The results of ultraviolet photoelectron spectroscopy show that the work function of PEIE-DBO-modified ITO is 3.94 eV,which is the lowest value among three polymers.Meanwhile,the conductivity and electron mobility of PEIE-DBO are higher than those of PEIE-DIO and PEIE-DCO,which is beneficial to electron transport and collection.The inverted PSCs have been prepared by using three polymers as ETLs and PTB7-Th:PC71BM blend film as the photoactive layer.Among them,the PSCs devices based on PEIE-DBO as ETLs show the best performance.The PSC shows a PCE value of 10.52%when the thickness of PEIE-DBO is 9 nm,and it still retains a high PCE of 9.09%at the thickness of 50 nm.This result indicates that PEIE-DBO possesses better electron transport property than the reported conjugated polymers in thick films.Furthermore,the result also indicates that the kind of anions also affect electron transport property of the polymers and the photovoltaic performance of the PSCs.