Preparation And Performance Of Low-cost Electron Transports Layer Based On Non-conjugated Polyelectrolytes

Polymer solar cells（PSCs）have gained wide attention due to their light weight,flexibility,solution processing and low cost.In the decades,tremendous efforts have been devoted to design and synthesize of new photoactive layer materials and interface materials,and improve preparation process,so the photoelectric conversion efficiency（PCE）of PSCs has been elevated to over 16%,which is closing to the requirement of commercial applications.Among of these,interface engineering plays an indispensable role in improving device performance of PSCs,which is carried out by adjusting work function of electrode and improving interface contact between photoactive layer and electrode in order to improve charge extraction and charge transport.Herein,two non-conjugated polymers have been synthesized by a simple step with low-cost small molecules and used as electron transporting layers（ETLs）in PSCs,and the effects of the structure of these polymers on electron transport and photovoltaic performance of PSCs have been investigated.The detailed content is shown as follows:A small molecular quaternary ammonium salt PMDETA-Br Bu and a polyelectrolyte PMDETA-DBO were synthesized by quaterisation reaction between N,N,N’,N’,N’’-pentamethyldiethylenetriamine（PMDETA）and 1-bromobutane（Br Bu）and 1,8-dibromooctane（DBO）respectively.The inverted PSCs were prepared with PMDETA,PMDETA-Br Bu and PMDETA-DBO as the ETLs and PTB7-Th:blend film as the photoactive layer,and the effects of the chemical structure of ETLs on electron transport property as well as photovoltaic performance have been studied.Compared with PMDETA,PMDETA-Br Bu with the structure of quaternary ammonium salt leads to a lower work function of ITO electrode,a less interface barrier,more efficient electron extraction and electron transport.Compared with PMDETA-Br Bu,PMDETA-DBO with a cross-linked structure results in a lower work function of ITO electrode,a less interface barrier,more efficient electron extraction and electron transport.Therefore,the PSCs based on PMDETA,PMDETA-Br Bu and PMDETA-DBO as the ETLs showed the power conversion efficiencies（PCE）of 8.03%,9.42%and 10.15%.That is to say,both the structure of quaternary ammonium salt and the cross-linked structure in ETLs are beneficial to electron transport of ETLs and photovoltaic performance of PSCs.The polyelectrolyte PEDETA-DBO was synthesized by quaterisation reaction between N,N,N’,N’,N’’-pentaethoxydiethylenetriamine（PEDETA）and DBO.The inverted PSCs were prepared with PEDETA-DBO and PMDETA-DBO as the ETLs and PTB7-Th:blend film as the photoactive layer,and the effects of side groups of the polymers on electron transport property as well as photovoltaic performance have been studied.Compared with PMDETA-DBO with methyl side groups,PEDETA-DBO with ethoxy side groups leads to a lower work function of ITO electrode,a less interface barrier,more efficient electron extraction and electron transport,so it shows better thickness-insensitive property.The PSCs based on PTB7-Th:PC₇₁BM as the active layer showed the PCE values of 10.12%and 7.43%when the thickness of PMDETA-DBO is 10 nm and 30 nm.However,the analogous PSCs showed the PCE values of 10.41%and 9.63%when the thickness of PEDETA-DBO is 10 nm and 50 nm.That is to say,PEDETA-DBO is the best thickness-insensitive polymeric ETL in inverted PSCs.Moreover,the inverted PM6:Y6 PSCs based on PEDETA-DBO showed a PCE of 16.32%,but the PCE values of the analogous PSCs based on Zn O and PMDETA-DBO as ETLs were 15.37%and 15.02%.This work not only brings the highest performance thickness-insensitive polymeric ETL but also provides an efficient strategy to design low-cost and thickness-insensitive polymeric ETLs for R2R industry in future.