Minority Carrier Lifetime Decay And Recovery Of N-type Crystalline Silicon/silicon Oxide/phosphorus-doped Polysilicon Composites

P-type crystalline silicon material dominates in commercial solar cells because of its low cost,simple process and high photoelectric conversion efficiency.However,there are also some disadvantages,such as sensitive to impurities,low minority carrier lifetime and serious degradation effect.However,there is still relatively little research on the degradation mechanism and degradation control technology of N-type crystalline silicon under the action of light field,thermal field and light-thermal coupling.In view of this,this paper had systematically studied the degradation mechanism and degradation control technology of N-type crystalline silicon under different conditions and its photoelectric conversion efficiency in bifacial TOPCon solar cells and the feasible applications.The main contents were as follows:First,an ultra-thin silicon oxide layer was prepared on an N-type Czochralski or N-type cast polycrystalline silicon substrate by the HNO₃-Si O_x method,and phosphorous-doped amorphous silicon films of different thicknesses(30 nm,50 nm,70nm)were deposited by plasma enhanced chemical vapor deposition,after different conditions of high temperature crystallization annealing(820?+450?nitrogen atmosphere and 820?+450?water vapor/nitrogen atmosphere H injection),the tunneling oxide passivation contact(TOPCon)was obtained N-type crystalline silicon/silicon oxide/phosphorus doped polysilicon composites,the results showed that when the deposition thickness of the phosphorus doped layer was 50 nm,the passivation performance was the best.On the one hand,the doped layer was too thin to completely passivate the defects and was easy to burn during metallization and sintering.On the other hand,the excessive thickness of the doped phosphorus layer during the annealing process,which led to the delamination of the polysilicon doped layer,and the diffusion of excessive phosphorus atoms led to serious carrier recombination.The passivation performance was reduced.Under the annealing crystallization condition of820?+450?water vapor/nitrogen atmosphere H injection,the passivation effect was the best.The reason was that H injection passivates the grain boundary of the N-type crystalline silicon/silicon oxide/phosphorus doped polysilicon composites sample and the dangling bonds in the crystal.The chemical effect reduced the composite effect of the material surface.Further using the TOPCon preparation process,a double-sided TOPCon solar cell was prepared on two substrates and examined its application feasibility.The results showed that the photoelectric conversion efficiency of the sample with N-type cast polycrystalline silicon as the substrate was 19.03%,which was comparable to 18.78%of the sample with N-type Czochralski silicon as the substrate,and had great application prospects.Secondly,after rapid thermal annealing(RTA)of the composite material,the N-type crystalline silicon/silicon oxide/phosphorus-doped polysilicon composites were studied using Raman spectroscopy(Raman),electrochemical capacitance(ECV)and EDNA2 software simulation techniques and its annealing degradation recovery effect under different conditions(450?nitrogen atmosphere,820?nitrogen atmosphere and 450?water vapor/nitrogen atmosphere H injection).The results showed that the passivation degradation of N-type crystalline silicon was caused by both thermal quenching effect and H spillover effect;Compared with the other two annealing processes,the lifetime recovery effect of H injection in 450?water/nitrogen atmosphere was the best.The reason was that H injection passivated the grain boundaries of N-type crystalline silicon/silicon oxide/phosphorus doped polysilicon composites and the hanging bonds within the crystals and reduced the surface recombination effect.In addition,the mechanisms of RTA-induced passivation degradation and H injection-induced recovery were similar to CZ c-Si and cast-mc-Si,because the volume saturation current density of cast-mc-Si was 20 times higher than that of CZ c-Si.In addition,it had a high effective minority carrier lifetime in the low carrier density region and captured part of electrons.Finally,the passivation degradation mechanism of N-type crystalline silicon/silicon oxide/phosphorus doped polysilicon composites with TOPCon structure on two N-type crystalline silicon substrates under high temperature(75?)illumination or high temperature and high humidity(85?+85%humidity)was studied by using Sinton passivation tester.The results showed that the minority carrier lifetime degradation of CZ c-Si was large,the lifetime after stabilization was still higher than that of cast-mc-Si,because the initial lifetime and stable lifetime of CZ c-Si were higher than that of cast-mc-Si.