Study On The High-Performance Thick-Film Photovoltaic Devices

Over the past few years,dramatic progress has been made in organic solar cells?OSCs?,with the highest power conversion efficiencies?PCEs?of single-junction devices exceeding16%.To meet the requirements of large-scale production,efforts should be devoted to develop high-performance OSCs with thick-film interfacial layer and photoactive layer.Besides,techniques for processing thick-film devices by green solvent should be systematically studied.Therefore,in this dissertation we focused on developing highly-efficient thick-film OSCs based on thickness-insensitive photoactive and electron transport materials.Firstly,on thick-film interfacial layer,a series of naphthalene diimide?NDI?based n-type conjugated polyelectrolytes?PNDIT-F3N-F,PNDIT-F3N-Cl,PNDIT-F3N-Br,PNDIT-F3N-BIm₄ and PNDIT-F3N-BArF₄?containing different counterions were prepared.The size of counterions showed great impact on the alcohol solubility and photophysical properties of conjugated polyelectrolytes?CPEs?.Besides,the self-doping behaviors of these CPEs are also highly correlated with their counterions species.Moreover,the charge transporting and electrode modification study results show that the counterion species and their substituent groups are critical to the electron mobilities and electrode modification ability of these CPEs as well as their performance in OSCs.OSCs with these CPEs as electron transport materials?ETMs?can deliver high power conversion efficiency?PCE?up to 10.5%,which maintained>9.5%even under thick ETMs of 80 nm.In addition,we used a series of absorption-tunable n-type water/alcohol soluble conjugated polymers(NNT-Br,NNTT-Br,NNTT_O-Br and NNTT_OO-Br)as ETMs to acquire PBDB-T-2Cl:IT-4F based OSCs.Devices with electron transporting layer thickness of 5 nm,20 nm,50 nm and 100 nm were systematically studied.Wherein the optimal thickness of NNT-Br,NNTT-Br and NNTT_O-Br are around 20 nm while that for NNTT_OO-Br is 50 nm.Finally,a high PCE of 14.1%was obtained,suggesting the thickness-insensitive property of these materials.With PNDIT-F3N-Br as electron transport materials,we studied the photovoltaic properties of thick-film photoactive layer material?naphthothiadiazole based polymer donor NT812?in non-fullerene organic solar cell.We used the non-halogenated solvent o-xylene as the processing solvent combined with 1 vol%N-methylpyrrolidone?NNP?,small molecule ITIC as acceptor material to fabricate non-fullerene organic solar cell.a slightly higher efficiency of 8.24%was achieved.Moreover,these devices are insensitive to the active layer thickness and exhibit excellent thermal stability.Furthermore,we used another small molecule IEICO-4F as acceptor,which have complementary absorption with NT812.We developed a time-dependent pre-aggregation approach to restrain the phase separation morphology and film thickness of blend film,and realized high performance thick-film OSCs.A high PCE of 10.31%was obtained when the active layer thickness at140 nm,and the PCE can still remain at 9.32%when the active layer thickness reaches 200 nm.Besides,we used another strategy,ie.,rearranging the backbone of a highly-crystallized copolymer for high-performance non-fullerene solar cells.A reioregular polymer 2TRR,which composing of 5-fluorobenzothiadiazole and thiophene subunits,showed poor photovoltaic performance because of high crystallinity and low mobilty.The rearrangement in the backbones of 2TRR results in a random copolymer 2TRA,which can enable good blend morphology,higher exciton generation rate,more efficient excitons dissociation and less charge recombination in non-fullerene solar cells.With O-IDTBR and IEICO-4F as the electron acceptors,highly-efficient solar cell devices with PCE of 10.08%and 12.06%,respectively,were achieved.Moreover,2TRA-based non-fullerene solar cells show wide compatibility with multiple processing solvents,low insensitivity to the active layer thickness,and excellent photostability.The combined advantages of 2TRA based solar cell including high efficiency,green-solvent processing,thickness-insensitivity and good stability indicated that 2TRA is a promising polymer donor for application in large-area OSCs modules through roll-to-roll technology,and the rearrangement design on polymer donors could be useful to design high-performance polymers for commercial application.Finally,we used a high mobility polythiophene derivative P4T2F-HD as donor material to fabricate thick-film non-fullerene organic solar cell.By using synthesis complex index to estimate the cost of a range of classic high-performance polymer donors,wherein P4T2F-HD has a relatively low synthesis complex index.We fabricated solar cell devices based on this low-cost polymer P4T2F-HD,with ITIC-Th1 as non-fullerene electron acceptor.The best PCE of 10.18%was obtained for the devices processed by non-halogenated solvent o-xylene without extra treatments.Besides,when the active layer thickness reaches 300 nm,the PCE can still remain above 9%,with the FF surpassing 70%.These results indicate that the combination of P4T2F-HD:ITIC-Th1 is compatible in large-scale roll-to-roll processing technology.