The Study Of Nanomaterials Application In Organic Solar Cells

Oragnic solar cells?OSCs?have played an important role in the research of new alternative energy.According to the energy loss mechanism of the process of photoelectric conversion,the design of materials?structure and technology are developed rapidly.Therefore,the photoelectric conversion efficiency?PCE?of OSCs is constantly refreshed and breakthrough by the improvement of optical and electrical characteristics.The day those photovoltaics become the most widely used energy even fully integrated with the energy production and living needs is no longer out of reach.There is still room for improvement in efficiency and stability,even though OSCs efficiency is approaching the industrialization standard.Further breakthrough in efficiency cannot only rely on the progress of materials and technology but also depend on the development of interface engineering.In this paper,we attempted to regulate two kinds of interfaces in OSCs devices by taking the unique advantages of nanomaterials to achieve higher efficiency by simple and smart method.One is the interface for exciton dissociation inside heterogeneous junction and the other is the interface between different functional layers.We analysis the mechanism of nanomaterials in OSCs in enhancing the efficiency from the perspective of the light utilization,interface characteristics and charge transfer behavior of the device.We devote in improving the performance and stability of inverted OSCs?i-OSCs?,and the results are as following:The most commonly used electron transport materials TiO₂ nano film usually with surface defects which couldn't contact with active layer idealy.We prepared carbon quantum dots?CQD?with carboxyl group and capped it on the sol–gel TiO₂ by self-assemble as the combined cathode buffer layer for i-OSCs.CQD with the virtues of excellent electrical conductivity and ease of synthesis.By control the concentration of CQD solution,we can easily adjust the properties of the self assemble interlayer.The CQD interlayer lowered the energy barrier for electron extraction and improved the compatibility between the metal oxide and organic active layers,leading to a reduced electron accumulation at the interface between charge transport layer and active layer.Thus,the interface charge recombination loss has been restained.In addition,a closer contact between different layers minimizing the contact resistance at interface as indicated by the remarkable reduced R_s.For i-OSCs with PCDTBT:PC₇₁BM and P3HT:PC₆₀BM active layer,we achieved an enhancement in PCE of19.77%and 18.50%.We fabricated a series of i-OSCs using low temperature processed ZnO/PEI?polyethylenimine?complex film as ETL and investigated how the thick of ZnO nano film influence device performance.For ZnO electron transport layer?ETL?device,PTB7:PC₇₁BM and P3HT:ICBA cell achieved PCE of 7.52%and 5.36%when ZnO is30 nm.For ZnO/PEI device,PTB7:PC₇₁BM and P3HT:ICBA cell achieved PCE of9.43%and 7.07%when ZnO is 26 nm.A thin ZnO film offered a better surface roughness.PEI passivated surface defects and filled the cracks,suppressing the leakage current.The active layer can form a better phase separation on a more suitable substrate,which is benefit for charge separation and extraction leading to an optimized device performance.Based on the results,we furthure doped PEI into active layer,which could also selfassembled on the interface of ETL to achieve a better device performance.We doped carbon nanoparticles?CNPs?with excellent photoelectric properties into P3HT:ICBA blend system,by changing doping ratio to achieve a highe PCE.After doping 3 wt%CNPs,PCE enhanced to 5.9%,while PCE of control device is4.12%.Doping in active layer resulted in a homogenous morphology with ideal domain size,which improved the efficiency of the splitting of exciton.CNPs also played a role of scattering center,leading to an enhanced incident light traveling path inside the active layer and light utilization.Doping method is low cost?simple and effective,which enhance the work efficiency of device by promoting the optical absorption and charge transport simultaneously without additional technology process.Furthermore,we also investigated the effect of NaLuF₄:Yb,Tm nanorod doped into active layer.By adjusting the doping concentration,19%enhancement of PCE is achieved.Meanwhile,we also doped nano Cdots?1-5 nm?into PEI cathode buffer layer?CBL?.Convinced by absorption/scattering measurement and extciton generation rate,an improved light absorption of active layer and excitons generated occrued in active layer.The series resistance R_S of doped device also has been reduced and charge carriers migration properties has been enlarged.By comparison of single electron device,the electron mobility of un-doped device is 2.7×10³ cm² V^-11 S^-1,and the electron mobility of doped device is 5.5×10³ cm² V^-11 S^-11 under optimized condition.This convinced that the electron mobility has been enhanced in Cdots doping device.Doping concentration has influence on film morphology which will in turn affect the active layer.Doping 1.0 wt%Cdots into CBL,the splitting probability of exciton has been maximization.The carrier recombination loses has been reduced with a better contact of CBL and active layer,leading to higher PCE with enhanced short-circuit current density and fill factor.Through comparison performance declining in 9 days,device with doped CBL device showed a better stability.