Interface Engineering For Lower Recombination In Organic/Si Heterojunction Solar Cells

Interface recombination velocity of silicon(Si)-based heterojunction solar cells accounts for more than 50%of the total recombination.In order to obtain high-efficient photovoltaic devices,silicon surface recombination velocity should be minimized in a very low value.By modifying the surface morphology of conductive conjugated polymer of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)(PEDOT:PSS)and device rear side contact improvement,we have obtained high-efficient hybrid solar cells based on Si/PEDOT:PSS at relatively low temperature(<150 ?).Current versus voltage,extra quantum efficiency(EQE),minority charge carriers lifetime detector,transient photovoltage(TPV),capacitance versus voltage,atomic force microscope(AFM),scanning electron microscope(SEM),Lycra microscope,scanning Kelvin probe microscope(SKPM),room temperature probe station and fixed angle spectral ellipsometry are used to analyze the photoelectric properties,recombination rate,surface morphology and contact resistance of the devices.The main work includes:1.Current light trapping strategy mainly relies on the nanostructures on the Si surface,which also results in surface recombination due to the large surface to volume ratio.Here,we develop a light trapping method to fabricate nanostructures on the surface of PEDOT:PSS layer via dry imprinting.Commercial compact disc is used as template to copy its textured pattern on PEDOT:PSS.From experiments and simulations,we demonstrate that this disc patterns imprinted on PEDOT:PSS layer are well suited for light trapping application.The patterned device shows stronger optical response and displays a 13%enhancement on short circuit current compared with the pristine one.Due to its simplicity,this imprinting method is also promising for other solar cells for fabricating high performance light trapping layers.2.Organic/silicon(Si)heterojunction has been widely investigated to build up an asymmetrical heterocontact for efficient photovoltaics.However,it is still unclear how the organic molecule structures can affect their electronic coupling interaction with Si.Here,two widely explored electron acceptors of poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)}(N2200)and[6,6]-phenyl-C61-butyric acid methyl ester(PCBM)are used to build up asymmetrical Si heterocontact to investigate their electronic coupling interaction.It is found that PCBM displays different electronic coupling with Si from N2200,which is ascribed to the various physical distance with Si based on a systematic and detailed density functional theory calculation.Organic layer incorporation not only suppresses the surface charge recombination velocity but also leads to an Ohmic contact between Si and Al.Therefore,a doping-free organic/Si heterojunction photovoltaic with a power conversion efficiency of 14.9%is achieved with PCBM layer.This work discloses a key factor affecting organic/Si electronic coupling interaction,which helps build up high quality Si heterocontact for solar cells and other optoelectronic devices.Furthermore,the simplified heterocontact achieved by a low temperature,solution processed and lithography-free steps has a dramatically improvement on conventional diffusion doped-silicon one at high temperature.