Polycrystalline Solar Cells Emitter Optimization Mechanism And Performance Research

The electrical properties of solar cells were focused and its influence whileoptimizing emitter was mainly studied. Combining with the industrializationdevelopment of solar cells, the optimization of emitter fabrication by phosphorusdiffusion and the secondary cleaning and optimization of the emitter surface by NAOS(Nitric Acid Oxidation of Silicon) method were researched. I-V characteristics, emittersheet resistance, minority carrier lifetime, EL (Electro-Luminescence) and IQE (InternalQuantum Efficiency) performance were tested to characterize and analysis the electricalproperties, emitter performance and spectral response of solar cells. Besides, themechanism of optimizing emitter and its influence to the electrical properties of solarcells were also expounded.By using of PC1D software, the relationship between the performance of solarcells and doping density of emitter, junction depth, FSRV (Front Surface RecombinationVelocity), sheet resistance, minority carrier lifetime were simulated, which shows themethod to improve the electrical properties. The emitter was optimized by means ofDSD (Double Sides Diffusion), comparing different emitter sheet resistance, improvingconventional diffusion process after analyzing the influencing factor of emitter sheetresistance when changing diffusion temperature, redistribution time and the amount ofphosphorus source. IQE test shows DSD can increase short circuit current by enhancingthe spectral response of solar cells at long wavelengths; EL and I-V characteristics testdisplay that the conversion efficiency of solar cells increase at first and then decreasealong with the increasing of emitter sheet resistance which indicates it may exist aoptimum value during the technological process. Applying lower diffusion temperaturesfor a longer duration results in significantly enhanced uniformity of emitter sheetresistance and higher gettering efficiency, which leads to higher conversion efficiency.With the purpose of lowering doping density of emitter and secondary cleaning,NAOS method was used for the farther optimization of the emitter surface. I-Vcharacteristics test demonstrates remarkable improvement on short circuit current andconversion efficiency; EL and IQE results reveal that NAOS method enhances the spectral response of solar cells obviously at short wavelengths which promotes shortcircuit current.Finally, the conversion efficiency exceeded16.65%were obtained when applyingthe technological process of solar cells after optimization with a mass production ofabout500PCS. Besides, the interrelationship of electrical properties was verified by thestatistical analysis of electrical properties data.