Study On The Interface Modification And Photovoltaic Performance Of Si/PEDOT:PSS Heterojunction Solar Cells

Si/PEDOT:PSS hybrid solar cell(HSC)is a simpler and a cheaper device than the traditional silicon-based solar cell(SC).Moreover,many of mature processes of the traditional silicon-based SCs can also be fully utilized to the HSCs.In order to pursue higher photoelectric conversion efficiencies,researchers have studied this kind of cells from all aspects,including improve the light absorption,reduce the charge recombination and optimize the electrodes,in order to collect carriers effectively.Therefore,the interfacial properties of p-typed polymer of PEDOT:PSS,which acts as the hole transport layer,as well as the interfacial between silicon substrate and the front or rear electrodes,play a crucial role in the dynamic process of carrier's transport in dopant-free HSCs.Based on the abovementioned,this paper aims to improve the photoelectric conversion efficiencies of Si/PEDOT:PSS HSCs by optimizing the contact performances of the related interfaces with the method of low temperature passivation technology.Meanwhile,nano imprint technology is also proposed to adjust the work-function of PEDOT:PSS and improve the electrical properties of PEDOT:PSS film in the vertical direction by means of change the molecular distribution inside the PEDOT:PSS film.The main work contents are shown as follows:(1)Quinone hydroquinone(QHY)solution was used to grafte semi quinone(QH)molecules on the silicon surface at low temperature to optimize the interfacial properties.The dangling bonds of Si surface gradually saturated with the continuous grafting of QHY on it and the chemical passivation made the coverage of the QHY monolayer on the Si surface reached 44.55% via XPS test,which greatly reduced the surface defect state density.The interface dipoles formed during passivation process make negative charges far away from the surface of n-typed Si substrate,and thus form a strong inversion layer on Si surface.The combined effect of the field effect and chemical passivation reduce the surface recombination tremendously,leading to the measured minority carrier lifetime increased from ten to about 500 microseconds.Moreover,the presence of QHY interface layer between Si substrate and real Al electrode reduces the work-function of the Al layer,forming the electronic selective passivation back contact,i.e.,contact characteristic between Si/Al turn from Schottky to Ohmic behavior,which is benefit to the collection of electrons.(2)The QHY passivation layer is applied to the Si/PEDOT:PSS HSCs and the performances of the HSCs are tested.On the one hand,in the Si/Al interface,the presence of QHY dipole leads to the shifting of silicon conduction band edge,which improves the overall built-in potential of n-Si/PEDOT:PSS HSCs and thus obtains a larger open-circuit voltage.On the other hand,the presence of QHY passivation layer makes the heterojunction contact ofn-Si/PEDOT:PSS interfaces mutate to p+n junction and the negative charge repulsion electrons on QHY benzene ring enlarge the barrier of n-Si and p+layer,which also enhances the overall built-in potential and accelerates the separation of photo generated carriers.Finally,through QHY modification,Si/PEDOT:PSS HSCs achieved an optimized efficiency of 13.3% and an open circuit voltage of 640 m V.This shows that organic grafting is a simple,efficient and low cost method to achieve high efficiency HSCs.(3)The nanostructures PDMS elastic template was used to regulate the gravitational embossing of PEDOT:PSS films in nitrogen atmosphere.Through the tests and analysis of AFM,surface topography,surface potential,conductivity we could concluded that the nano imprint makes the coulomb interaction between PEDOT and PSS decreases and thus leads to the phase separation,which not only changes the work-function of PEDOT:PSS,but also enhance the vertical conductivity of PEDOT:PSS film.