The Study Of Eco-Friendly Solvent Processed Active Layers For Highly Efficient Organic Solar Cells

Organic solar cells?OSCs?have drawn significant attention as a new generation of thin film photovoltaic cells in recent years,due to the advantages of simple preparation process,low cost,light weight and big potential to fabricate flexible devices.In-depth developing of both organic photovoltaic materials and devices have boosted the power conversion efficiency?PCE?to exceed 16%.In addition,significant progress in fast removable solvent additives,thick-film processing and long-term stability provides the possibility for the industrialization of OSCs.However,most efficient OSCs are fabricated with halogenated solvents with high toxicity,such as chlorobenzene?CB?,dichlorobenzene?DCB?,chloroform?CF?and1,2,4-trichlorobenzene?TCB?,which would result in health hazarding and environment pollution.Therefore,environment-friendly solvents are essential for large-scale OSC production in the future.In chapter 2,we summarized the progress of using environment-friendly solvents to prepare bulk heterojunction?BHJ?active layers.In this dissertation,several new types of eco-friendly solvents were applied to fabricate both fullerene and non-fullerene based devices,which could show great potential in the preparation of highly efficient OSCs.In chapter 2,terpinolene?TPO?,a natural and safe substance for food and cosmetic additives,was selected as a solvent to replace halogen solvents such as CB for solution processing of OSCs.We calculated Hansen solubility parameters?HSPs?of TPO,and found that Distance in Hansen Space?R_a?and Relative Energy Difference?RED?of TPO to PC₇₁BM acceptor were suitable to be a good solvent.With well-known PTB7 as the polymer donor and minor 1,8-diiodooctane?DIO?as the solvent additive,high quality BHJ film could be fabricated by using TPO as the solvent.In OSC devices,the TPO-processed PTB7:PC₇₁BM active layers could show PCEs of 6.42%.What's more,TPO-processed PTB7-Th-based OSC also showed PCEs of 7.01%.The results indicate the great promise of TPO in the OSC fabrication.In chapter 3,we utilized binary solvent strategy to improve the OSC performance.The combination of 1,4-dioxane?DIOX?and TPO gives a new type of non-chlorinated and non-aromatic binary solvent,whose optimized ratio of 58:42 is obtained via the calculation of Hansen solubility parameters and further confirmed by actual solubility tests.As a result,the binary mixture processed PTB7:PC₇₁BM and PTB7-Th:PC₇₁BM active layers in the conventional OSCs showed PCEs of 7.6%and 8.3%,respectively,while the PCEs could be elevated to 8.30%and 9.39%in inverted OSCs,respectively.All the photovoltaic performances are comparable or even slightly higher than the corresponding CB cases.Our results demonstrate the big potential of the mixed non-chlorinated and non-aromatic solvents towards environment-friendly fabrication of highly efficient OSCs.In chapter 4,we explored 2-isopropyl anisole?2-IPrA?as a new type of non-halogen but aromatic eco-friendly solvent to process FBT-Th₄?1,4?and its derivative PFBT4TDT90-EH10based active layers in thick-film fullerene OSCs.The active layers were optimized by the selection of both main solvents and solvent additives.In inverted OSCs,the 300 nm thick FBT-Th₄?1,4?and PFBT4TDT90-EH10 based active layers showed PCEs of 9.03%and8.09%,respectively.The PCEs are comparable with that achieved with the optimized DCB:CB mixture.In addition,2-IPrA also afforded a PCE of 7.55%for the J51:ITIC:IEIC based ternary non-fullerene OSCs.In chapter 5,we chose indan with as a new type of non-halogen but aromatic eco-friendly solvent to process PTQ10:ITIC-4Cl based non-fullerene active layer,in the absence of any solvent additive.In inverted OSCs,an optimized PCE of 13.93%could be achieved,which was the highest efficiency for OSCs being processed with an eco-friendly solvent.The efficiency is also much higher than 13.08%,13.43%,and 10.91%achieved for the chloroform?CF?,xylene?o-XY?,and carbon disulfide?CS₂?processed active layers,respectively.In addition,more than 11%PCEs could be realized for the Indan processed other non-fullerene systems including PTB7-Th:IEICO-4F and PM7:ITIC-4F.The results indicate that indan is one of the most promising eco-friendly solvent in processing of highly efficient and stable OSCs.