Design And Synthesis Of All-narrow Band Gap Organic Semiconductor Active Layer Materials And Their Applications In Semitransparent Organic Solar Cells

Semitransparent organic solar cell(ST-OSC)is an important class of organic solar cells(OSCs)that have the characteristics of power generation and high transparency.They can be used as power generation windows,which have broad application prospects in the field of building integrated photovoltaic(BIPV).However,how to simultaneously optimize and balance two competing parameters,the average visible light transmittance(AVT)and power conversion efficiency(PCE)of ST-OSCs,so as to improve the core performance parameters of the device,light utilization(LUE,LUE=PCE×AVT)is currently a big challenge for the development of ST-OSCs.The all-narrow bandgap(all-NBG)materials with strong absorption in the near-infrared(NIR)region and weak absorption in the visible region are the ideal choice for the active layer of ST-OSCs.However,at present,the high performance all-NBG materials for ST-OSCs are still limited.In this dissertation,a series of high-performance all-NBG organic semiconductor materials is designed and synthesized.Combined with device engineering,high-performance ST-OSCs are prepared.The relationship between molecular structure and photovoltaic properties are studied,which provided a guide for balance PCE and AVT,further improving LUE.1.Rational design of active layer materials to enhance the open-circuit voltage(VOC)and device efficiency without compromising transparency is crucial to realize the practical application of ST-OSCs.We designed and synthesized three new narrow bandgap(NBG)polymer donors,namely PCE10-2Cl,PCE10-SF and PCE10-2F,by incorporating chlorine,sulfur and fluorine functional atoms into the polymer donor PCE10(Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)])respectively.By incorporation of these functional atoms,all these polymer donors show lower energy levels than the PCE10,ensuring a significantly higher VOC.Especially,the NBG PCE10-2Cl having overlapping absorption with the NBG acceptor IT-4F(3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene)not only obtains a remarkably improved VOC,but also achieves an impressive short-circuit current density(JSC),delivering the champion PCE of 10.72%.The corresponding ST-OSC device,without any additional treatment,can obtain an PCE of 8.25% and an AVT of 33%.The results demonstrate that the combination of NBG donor and acceptor with overlapping NIR absorption is an important approach to realize high-performance ST-OSCs.2.Advanced NBG Y-series acceptors could not well match with the NBG donors,due to their mismatched energy levels and poor compatibility,resulting in a low PCE<10%.Herein,we adopt a facile terpolymer design strategy to improve the matching of Y6 with efficient NBG polymer donor PCE10.F and Cl atoms are introduced into PCE10 matrix to afford two series of terpolymers,namely PCE10-BDT2 F and PCE10-BDT2 Cl.Compared with PCE10,all terpolymers show deeper energy levels,higher extinction coefficients,enhanced face-on orientation and better compatibility with Y6(2,2’-((2Z,2’Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiaz olo[3,4-e]thieno[2’’,3’’:4’,5’]thieno[2’,3’:4,5]pyrrolo[3,2-g]thieno[2’,3’:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylide ne))dimalononitrile).Consequently,a PCE of 13.80% is achieved by PCE10-BDT2F:Y6-based device,nearly 40% higher than PCE10:Y6-based device.ST-OSC also achieves impressive PCE of 10.85% with AVT of 41.08%.An outstanding LUE of 4.46% demonstrates the successful balance of PCE and AVT.3.This dissertation further proposes a molecular weight-regulated sequential deposition strategy to balance the PCE and AVT of ST-OSCs,thereby improving the overall performance of the device.A series of NBG polymer donors PCE10-2F with different molecular weights were designed and synthesized.It was found that the preparation of PCE10-2F and Y6 bilayer films by sequential deposition method with molecular weight regulation is discovered to fine-tune the crystallinity of the polymers,not only favoring the formation of a dense and robust film,but also reasonably adjusting the compatibility of donor/acceptor to enhance interfacial contact.Thanks to the favorable morphology,efficient charge dynamics,and suppressed energy loss of active layer,a PCE of 14.53% is obtained for the PCE10-2F/Y6 all-NBG materials-based opaque device.At the same time,the sequential deposition process can more conveniently and precisely control the selective absorption of the active layer,and the corresponding ST-OSC devices obtained PCE of 11.11%～10.01% and AVT of 39.93%～50.05%.A champion LUE of5.01% is achieved for ST-OSCs without complex optical engineering,which is one of the best LUEs at present.4.There are various see-saw relationships among the performance evaluation parameters of multifunctional ST-OSCs,how to balance each parameter to maximize the performance of multifunctional ST-OSCs is the biggest challenge in current development.We employ the multi-component active layer spectral engineering strategy to improve the performance of multifunctional ST-OSCs,through introducing compound DA((2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione))with ultraviolet absorption and compound Y5(2,2’-((2Z,2’Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiaz olo[3,4-e]thieno[2’’,3’’:4’,5’]thieno[2’,3’:4,5]pyrrolo[3,2-g]thieno[2’,3’:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylide ne))dimalononitrile)with NIR absorption into the active layer of the NBG system and the wide bandgap(WBG)system respectively.The addition of DA can achieve red-shift absorption in the visible light region,thereby enhancing the AVT of the active layer.Its wider bandgap and deeper energy level can also further enhance VOC,while Y5 can form an alloy phase with the host acceptor,effectively regulating the morphology of the active layer.As a result,The NBG multi-component active layer system achieves an outstanding PCE 15.57%(a record efficiency for PCE10family-based devices),while the WBG multi-component active layer system can achieve an impressive PCE of 18.71%.Notably,the ST-OSC with 15 nm Ag based on NBG system can achieve a LUE as high as 5.10%.Consequently,for 25 nm Ag,the multifunctional ST-OSCs device based on NBG system has achieved a PCE of12.83%,an AVT of 31.35%,a LUE of 4.02%,and an infrared rejection rate(IRR)of90.3%,achieving with excellent comprehensive performance.