High-Performance D-A Copolymer Donor Based on Difluoroquinoxaline A-Unit with Alkyl-Chlorothiophene Substituents for Polymer Solar Cells

Side chain engineering with fluorine substitution is widely used to enhance photovoltaic performance of polymer donors in the research field of polymer solar cells(PSCs).However,fluorine substitution has disadvantages of complicated synthesis and high cost.Herein,we synthesized a novel D-A copolymer donor PBQ9 based on difluoroquinoxaline A-unit with chlorine substitution on its alkyl-thiophene side chains instead of fluorine substitution in the polymer donor PBQ6,which greatly shortens the synthetic route and reduces the cost.Interestingly,the optimized binary PSC with PBQ9 as polymer donor and m-TEH as acceptor demonstrated a high power conversion efficiency(PCE)of 18.81%(certified PCE of 18.33%by National Institute of Metrology,China)with a high fill factor of 80.59%,and the photovoltaic performance of the PSCs is insensitive to the different batches of the polymer donor.The results indicate that PBQ9 is a high-performance polymer donor and that chlorine substitution is an effective strategy to improve photovoltaic performance and reduce the cost of polymer donors.

Stable perovskite solar cells with efficiency of 22.6%via quinoxaline-based polymeric hole transport material

Poor stability of spiro-OMe TAD hole transport materials(HTMs)with dopant is a major obstacle for the commercialization of perovskite solar cells(pero-SCs).Herein,we demonstrate a series of quinoxaline-based D-A copolymers PBQ5,PBQ6 and PBQ10 as the dopant-free polymer HTMs for high performance pero-SCs.The D-A copolymers are composed of fluorothienyl benzodithiophene(BDTT)as D-unit,difluoroquinoxaline(DFQ)with different side chains as A-unit,and thiophene asπ-bridge,where the side chains on the DFQ unit are bi-alkyl for PBQ5,bi-alkyl-fluorothienyl for PBQ6,and alkoxyl for PBQ10.All the three copolymers are adopted as the dopant-free HTM in the pero-SCs.The planar n-i-p structured pero-SCs based on(FAPb I_(3))_(0.98)(MAPb Br_(3))_(0.02)with PBQ6 HTM demonstrated the high power conversion efficiency(PCE)of 22.6%with Vocof1.13 V and FF of 80.8%,which is benefitted from the suitable energy level and high hole mobility of PBQ6.The PCE of 22.6%is the highest efficiency reported in the n-i-p structured pero-SCs based on dopant-free D-A copolymer HTM.In addition,the peroSCs show significantly enhanced ambient,thermal and light-soaking stability compared with the devices with traditional spiroOMe TAD HTM.

n-Octyl substituted quinoxaline-based polymer donor enabling all-polymer solar cell with efficiency over 17%

Recently, the power conversion efficiencies(PCEs) of all-polymer solar cells(all-PSCs) have increased rapidly. To further increase the PCE of all-PSCs, it is necessary to create new donor polymers matching the polymer acceptors. In this paper, we synthesize a new quinoxaline-based polymer donor PBQ8 with n-octyl side chain on the quinoxaline unit, which possesses the same skeleton structure to the previously reported PBQ5(with isooctyl side chain). The effects of alkyl side chains on the physicochemical properties of the polymer donor were investigated. In comparison with PBQ5, PBQ8 exhibits stronger intermolecular interactions and better molecular packing. When blending with polymer acceptor PY-IT, the PBQ8:PY-IT based devices demonstrated a higher PCE value of 17.04%, which is one of the highest PCEs occurred in the all-PSCs. And the PBQ5:PY-IT(PCE 15.56%, Voc0.907 V, FF 69.72%, and Jsc24.60 m A cm^(-2)) is much lower. The PBQ8:PY-IT blend displayed more efficient exciton dissociation, better molecular stacking properties, preferable phase separation and higher mobility. These indicate that as an effective method, side chain engineering can improve the efficiency of the all-PSCs.