Performance Optimization Of Organic Solar Cells And Study On Inverted Solar Cells

With the aggravation of energy issues, green pollution-free solar energy will getmore attention and the organic solar cells (OSCs) are favored by many researchersbecause of its simple process, low cost, flexible and large area production. This paperillustrated the development of organic solar cells, devices’ structures, operatingprinciple and the preparation process of the devices. The OSCs with conventionalstructure based on PB, PTT-FTQ and P3HT as donor and the inverted solar cellsbased on cobalt oxide as hole-transporting layer were fabricated and the devices’performance was also optimized. The detailed results are summarized below.(1) The OSCs with conventional structure such as ITO/Hole transporting layer/Donor: Acceptor/LiF/Al were fabricated and the performance was optimized fromvarious aspects.With a new donor material PB and PC61BM as acceptor, the performance of OSCswas optimized from the ratio of donor/acceptor, the thickness of the active layer, theannealing temperature and the solvent type. The results showed that the differentratios of the donor/acceptor affected the active layer network structure which wasmainly reflected in the open-circuit voltage. The thickness of active layer mainlyaffected the photon absorption which was impacted on the short-circuit current density.The annealing temperature affected the new D/A molecular rearrangement, whichhave a great impact on the current density and the voltage. The solvent type mainlyaffected the surface morphology of the active layer. Under suitable conditions, thepower conversion efficiency (PCE) of OSCs was reached at1.30%.With another new donor material PTT-FTQ, the performance of OSCs wasoptimized by different acceptor and1,8-Diiodooctane (DIO) as the additive. Theshort-circuit current density of OSCs with PC71BM as acceptor was much greater thanthat with PC61BM as acceptor while the open-circuit voltage was slightly lower. Thisis mainly due to PC71BM has lower LUMO energy level and stronger spectralabsorption. The DIO additive had effects on the regulation of the active layermorphology. The PCE of PTT-FTQ: PC71BM system was2.78%and the PCE was2.09%with PC61BM system.With the classic donor material P3HT and PC61BM as acceptor, the performance ofOSCs was optimized from the different thickness of two hole-transporting layer(HTL). The results showed that the optimal thickness of PEDOT:PSS as HTL was30 nm, the PCE of the OSCs was reached at a maximum efficiency of2.86%. WhenMoO3was used as HTL and the thickness was10nm, the PCE was3.20%.(2) The OSCs with the inverted structure such as ITO/electron transporting layer/Donor: Acceptor/hole transporting layer/Al were fabricated with a new HTLmaterial cobalt oxide (II,III)(CoOx). The cobalt oxide was inserted as efficient HTLbetween the active layer and top electrode in the inverted OSCs with titanium(diisopropoxide) bis(2,4-pentanedionate)(TIPD) as an electron selective layer. Thedevice performances with different thicknesses of cobalt oxide were studied. Thedevice with CoOxexhibited a remarkable improvement in power conversionefficiency compared with that without CoOx, which indicated that CoOxefficientlyprevented the recombination of charge carriers at the organic/top electrode interface.The performance improvement was attributed to that the CoOxthin film can modulethe Schottky barrier and form an ohmic contact at the organic/metal interface, whichmake it a great hole-transporting layer. When CoOxthickness was10nm, the deviceefficiency was reached to2.72%, which approached the efficiency of conventionaldevice2.86%.