The Application Of Fullerene-based Interfacial Materials In Organic Solar Cells

Organic solar cells?OSCs?,as the conversion medium of solar energy,have attracted great attention due to the superior properties such as low fabrication cost,flexibility,light weight and large scale fabrication through roll-to-roll processability method.The single-junction device has shown a notable progress in the past decades of years,which has reached an accredited power conversion efficiency?PCE?at13%.However,the intrinsic bottleneck of the architecture caused by the mismatched energy level and the unbalanced carrier mobility in the device limit further improvement of the device performance.To solve these limitations,insertion of interfacial materials between the electrode and photoactive layer is an effective strategy,accordingly achieving remarkably high PCE.In this paper,several fullerene derivatives were synthesized as interfacial materials for OSCs and the relationship between device performance and molecular structure have been discussed.?1?Fulleropyrrolidine iodide derivatives(EMC₆₀)with different adduct numbers have been synthesized and applied as e lectron transport layers to achieve high-performance organic solar cells.For devices based on PBDB-T:ITIC-M,the performance of device largely elevates the PCE from 6.21%to 12.20%.Moreover,solar cells based on PTB7-Th:PC₇₁BM,PCE was improved from 5.83%to 9.79%with Tri-EMC₆₀0 as interfacial material.By studying the PBDB-T:ITIC-M system carefully,it was observed that the EMC₆₀ could efficiently optimize the energy level,reduce the interfacial barrier,enhance the electron extraction.Notably,fullerene interfacial materials have been applied in PBDB-T:ITIC-M-based devices for the first time.The result demonstrates that increasing the self-doping adduct numbers of the EMC₆₀ not only increase electron transport,but also improve the device's integrative performance.?2?Two easily accessible fulleropyrrolidine iodide with different side chains,such as carboxyl and ester group,named as FPI-A and FPI-E,respectively,were synthesized to function as cathode buffer layer in inverted solar cells.Both of fullerene materials successfully inhibit the surface traps of ZnO film and optimize the work function.In particular,FPI-A shows enhanced the electron mobility and extraction efficiency of interfacial film,resulting in a significant enhancement of device performance.An outstanding PCE of 9.47%based on FPI-A was achieved with PTB7-Th:PC₇₁BM as active layer.