The Design Of Spectrally Selective Electrodes And Its Application In Colorful Semi-transparent Organic Solar Cells

Organic solar cells are attracting lots of attentions because of their flexibility,low cost and easy fabrication.Specially,the colorful semi-transparent organic photovoltaics(ST-OPVs)provide infinite possibility for business applications.Recently,the colorful devices have been fabricated through taking use of different colorful organic materials or optical structures such as Brag’s reflector mirror,photonic crystals or Fabry-Perot(F-P)resonant cavity.However,the demanding on aesthetics of colorful devices in building integrated systems and smart electronic devices is continuously increased.Hence,the design and fabrication of colorful ST-OPVs with high color purity and high efficiency are in high priority.Firstly,the F-P cavity was overlaid for designing the spectrally selective electrodes(SSEs)with high color purity.Thermal evaporating the Al:Ag layer being the reflecting wall,Lithium Fluoride(LiF)and Molybdenum Oxide(MoO3)being the cavity medium,we got two symmetric double-layered F-P cavity SSEs with high color purity.However,the thick reflecting wall decreased the transmission,which would limit the development and application of the double-layered F-P cavity SSEs.To achieve the aim of high color purity and high transmission at the same time,the bionic SSEs inspired by the colorful beetle shell was designed.Based on theoretical calculation,we chose a high refractive index dielectric materials(N,N’-diphenyl-N,N’-(1-naphthyl)-1,1’-bipheny 1-4,4’-diamine,NPB)and a low refractive index material(LiF)to change the optical admittance of the metal(Al:Ag)film.The constructed SSEs contained three parts.The first part mainly provided the conducting ability.The second part generated a high transmission peak with a low full width at half maximum(FWHM),thus selecting spectrum.The third part of fluorocarbon(CFx)acted as an anti-reflective layer and encapsulating coating.We fabricated the metal and dielectric layers through thermal evaporation and fabricated CFx layer through chemical vapor deposition.We finally got several SSEs with high color purity(highest value to be 65.27%)and high transmission(highest value to be 99.49%).The square resistance of these SSEs showed values smaller than 19.27 Ωsq-1.Furthermore,we combined these bionic SSEs with the ternary active material(PM6:N3:PC71BM)to fabricate the colorful ST-OPVs with conventional structure.Compared to the reference device using 15 nm Al:Ag film as the electrode,colorful devices obtained higher absorption in visible spectrum range,thus increasing photoelectric conversion ability.The colorful ST-OPVs reached an optimized power conversion efficiency(PCE)of 15.07%.The transmission characterization results showed high color purity approaching 100%and a highest transmittance of 29.70%.Besides,the stability testing results demonstrated that the colorful ST-OPVs showed better photoelectric and spectrum stabilities than the reference device.Therefore,the colorful ST-OPVs based on the bionic SSEs exhibited high efficiency,high transmission,high color purity and good stability at the same time.