Interface Optimization And Performance Improvement Of Dopant-free Silicon Heterojunction Solar Cells

With the increasing energy demand,solar cell power generation has become an effective way to solve energy crisis due to its safety,environmental protection and sustainability,in comparison with fossil fuels,such as coal,oil and natural gas.To date,conventional crystalline silicon（c-Si）solar cells have been the mainstream products in the photovoltaic industry due to their high stability and high efficiency.Nevertheless,the high-temperature diffusion,ion implantation and other complex process significantly increases the fabrication cost and limits its further development.Although organic solar cells have caused serious concern for easy process and low cost,poor stability and low energy conversion efficiency limits their future application.Organic-silicon heterojunction solar cells have drawn great interests and show great research value and application prospect due to combined advantages of high mobility,high stability and well developed fabrication process from inorganic materials and the properties to adjust organic molecule structure from solution processable organics.This kind of solar cells not only combine the mature silicon-based solar cell technology and keep the high efficiency advantage theoretically,but also avoid the high-temperature diffusion and complex process,which can be expected to reduce costs in the future.The reported highest power conversion efficiency（PCE）has achieved over 16%.This paper is based on the Si/PEDOT:PSS heterojunction solar cells and mainly focuses on the interfacial properties with semiconductor and metal.In this paper,the device performance influenced by the interfacial properties has been discussed in depth.The main work of this paper includes:1.Low resistance structure of n-Si/AZO/Al and then high performance Si/PEDOT:PSS heterojunction solar cell was achieved by inserting inorganic semiconducting AZO（Al doped ZnO）thin films at the metal/semiconductor interface.Specifically,the AZO nanocrystals were synthesized with zinc acetate dihydrate and doping source of aluminum nitrate nonahydrate by solution process.The contact resistivity（ρ_c）down to 3 m?·cm² was quantified by varying the anneal temperature and doping concentration（Al atoms in ZnO solution）.Combined with X-ray photoelectron spectroscopy,ultraviolet photoelectron spectroscopy,atomic force microscope and fourier infrared spectrometer,detailed investigations on film morphology and chemical status near the interface revealed that annealing the AZO films at 200°C is beneficial to improve the film uniformity and the doping efficiency,while the presence of Al-O-Si bonds on the silicon surface may help to reduce the density of Si dangling bonds and suppress interfacial charge recombination.Finally,by utilizing 200°C-annealed AZO thin film with 10 mg/ml doping concentration,n-Si/PEDOT:PSS heterojunction solar cells with enhanced PCE of over 13.6%and open-circuit voltage(V_oc)of 640 mV was achieved.2.Alkaline inorganic material barium hydroxide inserted at the metal/semiconductor interface could passivate the silicon surface,suppress interfacial recombination and future improve the device performance.Specifically,the high minority carrier lifetime and high implied V_oc was quantified by varying the annealing temperature and solution concentration of the Ba（OH）₂ layers.What’s more,it was found that barium hydroxide could lead to an ideal Ohmic contact at the metal/semiconductor interface,while keeping good passivation performance.Finally,the PCE,V_oc and short-circuit current density(J_sc)of Si/PEDOT:PSS heterojunction solar cells was improved by utilizing 100°C-annealed Ba（OH）₂ films with 10 mg/ml solution concentration.