Solution Processed Carrier Selective Layer For Crystalline Silicon Solar Cells

At present,the domestic and international photovoltaic market is dominated by crystalline silicon solar cells based on heavy doping carrier transport layer and direct metallization contact technology.From the perspective of manufacturing technology,the heavy doping of crystalline silicon surface as electron(heavily doped with phosphorus)or hole(heavily doped with boron or aluminum)transport layer requires high temperature and high vacuum equipment in the doping process,and the manufacturing process involves toxic gases,which undoubtedly increases the requirements on the manufacturing process and increases the manufacturing cost.From the perspective of device performance,the high concentration of doping on the surface of crystal silicon will cause parasitic absorption and introduce a large number of defects in crystal silicon lattice structure,leading to significant Auger recombination and loss of photogenerated carriers.Based on these still unsolved scientific and technical problems,photovoltaic researchers have pushed forward the research of new carrier transport materials.There are four basic requirements for new carrier transport materials.First,the surface of crystal silicon is doping free;Second,the efficient and selective transfer of electrons or holes in crystal silicon;Third,try to meet the low temperature technical route;Finally,the requirements for equipment should be as simple as possible.Based on these four basic requirements,this paper carries out the following work:(1)To explore the feasibility of synthesizing transition metal chromium oxide film by solution method as the hole transport layer of silicon based solar cells.Based on the method of nitrate solution self-propagating combustion synthesis,the thin films were prepared by spin-coating the silicon wafer with the mixed precursor solution of chromium nitrate and glycine and then heating.Solution method of synthesis of chrome oxide film work function test of 4.8 e V,and contact resistance of silicon as low as 532.4mΩ·cm~2,applied to the p-type silicon solar cell test device after the photoelectric conversion efficiency as high as 16.1%,compared with the direct metallization devices(15.2%)in the device performance has a certain degree of improvement.(2)Modified chromium oxide thin film by copper doping and air annealing for solar cell hole transport.After proving that the solution synthesized chromium oxide thin film is feasible to be applied to silicon based batteries,we doped the chromium oxide thin film and adjusted the annealing process to further improve the electrical properties of the film.After mixing copper film annealed at 150℃work function of5.04 e V,contact resistance as low as 94.8 mΩ·cm~2,applied to the p-type silicon battery test device after the photoelectric conversion efficiency as high as 16.9%,compared with the direct metallization devices(15.2%)and chrome oxide thin film devices(16.1%)had obviously improve the photoelectric conversion efficiency.(3)The electron-selective transport layer prepared by solution method can improve the contact resistance of n-type silicon electron transport interface.Based on two theories of improving contact resistance,metal salt with low work function was selected to induce band bending on crystal silicon surface and macromolecular organic matter was used to adsorb silicon surface to treat partial suspension bond to reduce surface pinning effect to achieve selective electron transport.Sodium gluconate/silicon contact resistance as low as 1.3 mΩ·cm~2;Tween-20/silicon contact resistance as low as 5.8mΩ·cm~2.Sodium gluconate was applied to the crystal silicon solar cells with photoelectric conversion efficiency of 16.1%,Tween-20 was applied to n-type crystalline silicon solar cells with photoelectric conversion efficiency of 15.3%.