Design And Synthesis Of Novel Nonfullerene Acceptors And Water/Alcohol Soluble Conjugated Polymers For Organic Solar Cells Applications

In the past two decades,organic solar cells?OSCs?have attracted many attentions in the international academic community as emerging photovoltaic technologies with low cost,low energy consumption,solution processing,flexible roll-to-roll processing,and environmental friendly advantages.From 2015 to the present,with the rapid development of nonfullerene acceptors,the power conversion efficiencies?PCEs?of OSCs devices have continuously achieved new records.Among them,the nonfullerene small molecule acceptors and the acceptor polymers play a key role in the active layer of the corresponding highly-efficiency device,respectively.Water-soluble polymers play an important role in device interface modification due to their unique physical and chemical properties.This thesis focuses on the research of materials and device properties for OSCs,which can be divided into the following three parts:one is the study of small molecule nonfullerene acceptors and related OSCs devices;the second is n-type polymers for all-polymer solar cells;the third is the synthesis of water-soluble polymers and their cathode interface modification properties.In Chapter 2,in order to overcome the excessive aggregation of perylenediimide?PDI?units,we investigated the relationship between the degree of non-planar configuration of PDI based acceptors and the morphology of the blended films and OSCs applications.The three PDIs display different non-planar geometrical structures because of the different linker units,which affect the corresponding morphology of the blend films and also influence the charge mobility and fill factor?FF?of OSCs.As the result,the P4N4 based nonfullerene devices show the best photovoltaic performance with a PCE of 5.7%.These results indicate that the spatial conformational regulation for the linker units of PDIs is an effective method for designing efficient nonfullerene acceptors.In Chapter 3,OSCs with extremely high V_oc and extremely low voltage losses were fabricated by employing perylenediimide-based nonfullerene acceptors?SFPDI,PDI4,and PDI6?and narrow bandgap polymer donor?BDT-ffBX-DT?with deep-lying HOMO level.The SFPDI-based device shows the PCE of 6.2%with an impressive V_oc of 1.23 V,which is among the highest PCEs for OSCs with a V_oc>1.20 V.The high V_oc and low V_loss of the BDT-ffBX-DT:PDI solar cells were revealed to be originated from low nonradiative recombination losses(?V_oc,nr)as evidenced by the relative high electroluminescence quantum efficiency(EQE_EL)of OSC blends(10^-5–10^-4).To the best of our knowledge,the?V_oc,nrc,nr of BDT-ffBXDT:SFPDI device?0.20 V?is the lowest value reported to date for OSCs.Such a low?V_oc,nrc,nr is also approaching that of high performance crystalline silicon and perovskite solar cells.These results thus show that OSCs have the potential to achieve photovoltages and voltage loss fully comparable to inorganic and hybrid solar cells.In Chapter 4,we have developed a nonfullerene acceptor?ITIC-OE?with a high relative dielectric constant of up to 9.5 for application in OSCs.The ITIC-OE single component based device exhibits significant photocurrent compared to ITIC.A high PCE of 8.5%was achieved,which is the highest value for bulk-heterojunction OSCs that employ high dielectric constant materials.The characterization of the intrinsic physical and optoelectronic properties suggests that ITIC-OE is promising for making highly efficient OSCs.In practice,the ITIC-OE-based devices show a slightly lower device performance than the reference ITIC devices,which is a collective result of imbalanced hole/electron transport,enhanced recombination losses,and a less optimal BHJ morphology.The essential reason is the reduced crystallinity of ITIC-OE and too good miscibility between ITIC-OE and the polymer donor PBDBT,which in turn results in blend films lacking proper microphase separation.Further research involving high dielectric constant organic semiconductors should therefore focus on improving the dielectric constant and modulating the morphology simultaneously,which could be realized by rational molecular design.In Chapter 5,we propose a new design idea for achieving the optimal morphology,high efficiency,and high stability all-polymer solar cells.As a result,the best all-PSCs based on the NOE10 show a PCE of 8.1%and a record high FF of 0.75 using the novel acceptor polymer?NOE10?.The all-PSCs based on NOE10 show excellent storage lifetime and thermal stability with>97%of the initial PCE after 300 h of aging at 65?.Also on this system,the ternary all-polymer solar cells which achieve 8.5%of PCEs with a wide range of addition ratios are achieved by the addition of the third component polymer.Our work demonstrates an effective strategy for forming optimal blend film morphology for all-PSCs and also shows the excellent potential of NOE10 as an alternative to commercial acceptor polymers for future technological applications.In Chapter 6,we designed and synthesized a series of high-efficiency,high-light transmittance water-soluble polymers,specifically with a neutral amine group and a corresponding quaternary ammonium bromide in the side chain,and the main chain contains different sulfur oxidation states.The polymers show good cathode interface modification properties,and OSCs fabricated using these polymers as cathode interface layers can achieve PCEs of 8-9%.