The Study On High Efficiency N-Type Back Contact Silicon Solar Cell Technology

At present,crystalline silicon solar cell is still the dominant product in the photovoltaic power generation.A key factor for the photovoltaics to be low price is to develop more efficient solar cell and reduce the production cost as well.The high-efficient n-type interdigitated back contact?IBC?solar cells have no light induce degradation and could reach to very high conversion efficiency,thus they were been studied by so many people.In this paper,we main investigate on solving the key technologies of high efficiency and low cost IBC cell that can achieve industrial mass production.First,the effect of carrier transport and pitch width on the cell performance parameters were analyzed by numerical simulation.Then the surface recombination characteristics and passivation mechanism of IBC cells were systematically studied.The high efficiency IBC solar cell based on industrial equipment was prepared and the application of passivated contact structure in IBC cell was analyzed.Finally,the characteristics of IBC modules were studied.The main results are as follows:1.By using numerical simulation with Quokka software,compared different front surface structures.The Front Floating Emitter?FFE?IBC cell is propitious to the transfer and collection of minority carriers on the front surface.The“electric shielding”effect can be effectively reducing and the recombination of carriers can be reduced in the wider back surface field?BSF?width.And the required range of the front surface dopant process window is wide.With the increasing of pitch width on the back surface?the ratio of emitter increases?,the minority carriers are more likely to be collected and the short-circuit current density increases accordingly.But at the same time,it also leads to the increasing of the lateral transmission resistance of the cell,which results in the decrease of the fill factor.The width of the pitch,emitter and BSF are 1.4mm,980?m and 420?m,respectively.The resistivity requirement for wafers of FFE IBC cell is wider than FSF IBC cell.IBC cell with FSF structure,efficiency depends on the resistivity of wafer to a large extent and increases with the resistivity.The specification of silicon wafer is determined as follows:lifetime is more than 2ms and the resistivity range is 3?·cm²0?·cm.2.The surface recombination and passivation performance of IBC cell were analyzed.The optimum effect of SiO_x:B passivation layer with different thickness can be obtained by testing the structure of SiO_x:B passivation layer with 20nm thickness.The results of SiO_x:B passivation were better than that of SiO₂ passivation layer grown by wet chemical method,and the passivation effect was similar to that of thermal oxidation.3.The preparation technology of IBC cell were studied from wafer cleaning,front surface doping and metallization contact,respectively.The Implied V_oc with symmetry test structure is higher than 700mV and saturated current density of J₀ is lower than 50fA/cm².The cell efficiency could reach to 22.83%.By comparing different pitch width and emitter ratio,the average efficiency could reach to 22.80%with 1.1mm pitch width and 73%emitter ratio,respectively.The resistivity experiment shows that the low-doped high-resistivity wafer is suitable for IBC cell.IBC cells with Al₂O₃ and SiO₂ passivated layer were studied.Al₂O₃ thin film can improve the cell efficiency significantly.But the cells with Al₂O₃passivation are prone to charge mismatch under reverse bias voltage.The decay occurs during illumination,which is restored to the initial state after annealing at low temperature.While the IBC cell with SiO₂ passivation layer does not decay obviously.4.Passivated contact structure based on doped poly-Si and ultra-thin oxide layers are developed.The role of oxide layer was investigated.In order to further improve the efficiency of IBC,passivated contacted technology became the main contact of research.The study found that,the oxide layer to be critical for hindering the penetration of dopant source into the silicon bulk,stopping epitaxial grow between the top ploy-Si film and the underlying crystalline silicon.The influence of anneal temperature on passivated performance was studied.The results show that optimum anneal temperature can reduce recombination of surface and metal contact area obviously.Development of a low-cost and industrially feasible technology with combined passivated contacted technology and IBC solar cell.The fabricated cell efficiency with 156.75mm×156.75mm large area could reach to 23.47%.5.The process of encapsulation technology on IBC solar cell was investigated.The glass to glass modules with low temperature solder half cell were used and the power could reach to 330W.Because of the low reverse breakdown voltage,the power loss and the heat transferred of IBC module will be significantly reduced when hot spots occurred.