Research On High Efficiency Organic Tandem Solar Cells

Organic solar cells have the advantages of light-weight,sollution-processability,and can be prepared for large-area flexible devices by roll-to-roll printing,which have developed rapidly in recent years.Benefit from the development of new materials,the designing of device structure,the optimization of active layer morphology,the power conversion efficiency of single-junction OSCs has been exceeded 16%.However,single OSCs are always facing challenges.One is that the absorption spectrum of the donor and acceptor materials are narrow,and they cannot absorb the sunlight effectively.The other is that when the photon excites the electronic transition of the active layer material,the photon energy is larger than the optical band gap of the active layer material,which will lead to heat loss.In this paper,we mainly focus on the synthesis of broad absorption spectrum material and the tandem OSCs to reduce the heat loss caused by optical band gap.The main contents are as follows:a.A novel non-fullerene acceptor-donor-acceptor structured small molecule acceptor material with fused ring N-alkyl dithieno[3,2-b:2',3'-d]pyrrole(DTP)as the central donor unit and((2-(5,6-difluoro-)3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile)(EG-2F)as the terminal acceptor unit,named DTP-C17-4F,was designed and synthesized.The optical absorption spectrum of the material was measured by UV-Vis spectrophotometer,and its optical band gap was calculated to be 1.38eV,and the absorption edge could be broadened to 900nm.The HOMO and LUMO of DTP-C17-4F are-5.59eV and-4.16eV respectively.DTP-C-7-4F demonstrates strong near-infrared absorption,suitable energy levels,good film morphology and high electron mobility,resulting outstanding short-circuit current density of 21.17mA/cm2 without the additives for organic photovoltaics.b.We designed and fabricated inverted organic tandem devices with structures of ITO/SnO2/PBDB-T:IT-M/MoO3/Ag/PFN-Br/PCE10:IEICO-4F/MoO3/Al and ITO/SnO2/J71:IT-M/MoO3/Ag/PFN-Br/PCE10:IEICO-4F/MoO3/Al,which obtained PCE of 11.41%and 11.51%respectively,surpassing single-junction solar cells.Among them,the tandem cell with J71:IT-M as the front junction active layer achieves a higher VOC of 1.62V and a lower voltage loss of 0.04V.The PCE of the two tandem devices are more than 11%under different light intensities.and the devices can work effectively.The encapsulated tandem devices exhibited good stability with high photovoltaic characteristics value after 100 hours of continuous light in air.