Preparation And Photoelectric Properties Of Silicon/Organic Heterojunction Solar Cells

With the overwhelming advantage in terms of high power conversion efficiency,excellent stability and mature scale processing technology,the crystalline silicon(c-Si)solar cells have dominated the world photovoltaic market.In the past decade,due to the optimization of the structure of devices and the application of new materials,the laboratory photoelectric conversion efficiency of single-junction c-Si solar cells had increased to 26.7%,approaching the theoretical limit efficiency.However,the process of forming p-n junctions in c-Si solar cells always required high-temperature diffusion to form heavily doped region.The heavily doped region leads to severe optical parasitic absorption and Auger recombination,which will limit the improvement of cell efficiency;secondly,the process require the use of expensive equipment and toxic precursor gases limit the reduction of manufacturing cost.Therefore,the exploration of new functional material or simple preparation technique is one of the current development directions for Si-based solar cells.The dopant-free heterojunction technology provides a possible direction for the low-cost preparation of high performance Si-based solar cells.Dopant-free Si/organic heterojunction solar cells using n-type c-Si as substrate and conducting polymer PEDOT:PSS as a hole-selective contact material have received wide attention from researchers because of their advantages such as simple preparation process and a low-cost,etc.In this thesis,we aim to prepare high-efficiency Si/PEDOT:PSS heterojunction solar cells,focusing on the intrinsic property of the PEDOT:PSS film,the light capture capability of the silicon substrate,the interfacial property and structure on the photovoltaic conversion performance of the device.The main research contents are as follows:1.Zn(TFSI)2 modulates the conductivity of PEDOT:PSS film to improve the photovoltaic performance of Si/PEDOT:PSS heterojunction solar cells.By doping the PEDOT:PSS aqueous solution with ionic liquid Zn(TFSI)2,an increase in the size of conductive component PEDOT grains and a decrease in the insulating component PSS are caused by the interaction between the ions.This structural rearrangement effect results in the phase separation of PEDOT and PSS to create more conductive channels and improve the charge transport property.The Si/PEDOT:PSS heterojunction solar cells with an efficiency of 12.1% was obtained by combining the PEDOT:PSS film with high passivation ability and high conductivity,respectively.2.Graphene oxide(GO)modulates the work function of PEDOT:PSS film to improve the photovoltaic performance of Si/PEDOT:PSS heterojunction solar cells.By depositing GO film with high work function on the PEDOT:PSS film,the work function of PEDOT:PSS film is increased to 5.08 e V due to the electron absorption ability of GO,which promotes further bending of the energy band in silicon and the formation of strong inversion layer.Additionally,the refractive index of GO satisfies the double layer antireflection mechanism,causing the reflection of the Si surface to reduce.The combination of these two functions increase the efficiency of Si/PEDOT:PSS heterojunction solar cells to 13.8%.3.Preparation of full-contact heterojunction solar cells with pyramidal structured Si and PEDOT:PSS thin film.Random pyramidal Si were prepared by alkaline chemical etching and the top corners of the pyramids were smoothed.By modifying the aqueous PEDOT:PSS solution with sodium alginate,a completely tight contact between the PEDOT:PSS film and the pyramidal structure silicon substrate was formed due to the enhanced adhesion of the aqueous PEDOT:PSS solution.The Si/PEDOT:PSS heterojunction solar cells with an efficiency of 15.4% was prepared by combining the PEDOT:PSS film with high adhesion layer and high conductivity layer,respectively.4.Improved Al/Si contact performance to enhance the photovoltaic performance of Si/PEDOT:PSS heterojunction solar cells.By introducing the n-type organic semiconductor PCBM at the Al/Si interface,the Schottky contact between Al/Si was transformed into an ohmic contact of Al/PCBM/Si,resulting in a significant reduction of the contact resistance at the interface.Treating the Si surface with TMAH,the generated silicon oxide reduced the density of defect states on the Si surface and effectively suppressed the carrier recombination at the interface.The Si/PEDOT:PSS heterojunction solar cells with an efficiency of 14.6% was obtained by appropriate interfacial chemical treatment and the introduction of PCBM film as the electron transport layer.5.Preparation of back-contact Si/PEDOT:PSS heterojunction solar cells.Back-contact structured Si/PEDOT:PSS heterojunction solar cells with Nafion as the front passivation and anti-reflection layer,buried Li Ac/Al structure as the electron-selective contact layer,and fully covered PEDOT:PSS/Ag as the hole-selective contact layer were prepared by solution method.Among then,the Li Ac thin film prepared by the solution method was patterned by using the plasma etching process.This method of preparing the patterned film without the photolithography process provides a new idea for the preparation of back-contact cells by the solution method.The preparation process is simplified due to the near-insulation between PEDOT:PSS and Al.Finally,back-contact structure Si/PEDOT:PSS heterojunction solar cells with an efficiency of 15.4% was prepared by a simple solution processing method.