Molecular Design And Characterization Of Alkylthio Side Chains Based Organic Photovoltaic Materials

With the rapid development of the economy,the energy requirement has become a major obstacle to social progress.With the depletion of traditional fossil energy,it is urgent to develop new energy sources with high efficiency,cleanliness and large reserves.As promising renewable energy,solar energy has attracted worldwide attention due to its inexhaustible,inexpensive,environmentally friendly and widely distributed characteristics.In the past few decades,silicon solar cells have developed vigorously,and the power conversion efficiency has reached over 20%,exhibiting excellent performance in aerospace and other fields.However,the fabrication process of silicon solar cells is suffered from pollution and high cost,limiting the further expansion of its application field.Therefore,the development of new photovoltaic technology has become a new research focus.Organic solar cells possess many advantages,such as light weight,flexibility and low cost,showing great potential in the field of flexible electronic devices,At present,the efficiency of single junction organic solar cells has exceeded 14%and the efficiency of tandem cells has exceeded 17%.How to further improve the efficiency and stability of organic solar cells is still worth further investigation and the innovation of active layer(absorbing layer)is the most important researching topic.In this paper,we focus on improving the photovoltaic performance of high-efficiency organic photovoltaic materials by using alkylthio side-chain substitution to fine-tune the energy levels and absorption features.The research includes:1.A new A-D-A type small molecule containing benzo[1,2-b:4,5-b']dithiophene as the core unit,terthiophene as the 'arm' and 3-ethylrhodanine as the end group(namely BDTT-S-TRS)was designed and synthesized as donor material.BDTT-S-TRS exhibits a deep HOMO energy level of-5.22 eV and a red-shifted absorption edge of 725 nm.When blended with PC71BM(as the acceptor),the device showed a high power conversion efficiency(PCE)of 8.07%,with a high fill factor(FF)of 70.5%.2.Three new D-?-A type polymers containing benzo[1,2-b:4,5-b']dithiophene with different substituted thiophene(such as alkylthio chain,alkyl chain and silane chain)as the donor unit,5,6-difluoro-2H-benzo[d][1,2,3]triazole as the acceptor unit(namely CP24,CP27 and CP31 respectively)were designed and synthesized by introducing alkylthio side chains on the ?-bridge.The introduction of alkylthio substitutent on thiophene ?-bridge made the main chain more twisting,resulting in the lower carrier mobilities compared to the alkyl chain based counterparts.By using m-ITIC as acceptor,the CP27 based device showed an excellent PCE of 8.08%,with a high Voc of 0.93 V.After adding PC7,BM as the third component,the CP27 based ternary devices showed an improved PCE of 8.66%.3.Three new alkylthio side chain based A·D,A type small molecules containing indacenodithiophene as the core unit with different end groups(namely CS57,CS70 and CS77,respectively)were designed and synthesized as acceptor materials.The three acceptors exhibited strong absorption in the wavelength of 600-800 nm,complementing with the wide-band gap polymer donors.By using CS57 as acceptor to blend with PBDB-T(as the donor),the device showed a high PCE of 13.72%.After changing the donor to PTQ10,the device showed a high PCE of 12.20%.Meanwhile,the PTQ10:CS57 based device possesses a high Voc above 1 V with a relatively low voltage loss of 0.47 V.