The Study Of Preparation Of Silicon Nanowire Solar Cells And Their Interface Passivation Mechanism

At present,environmental issues have become increasingly prominent,and developingnew energy sources has become an urgent task.Among all new energy sources,solar cells have been favored for their cleanliness and renewability.Recently,silicon nanowire solar cells are in the forefront of solar cell researchdue to their low reflectivity,abundant material sources and easy preparation for large areas.In this thesis,the author focuses on the problems of the lower open circuit voltage and seriously recombination in the back surface field of silicon nanowire cells than that of traditional bulk silicon cells.A new approach using transparent transition metal oxide films,which has good transmittance and high work function and hole selective transmission,totransport photogenerated carriers separately and passivatethe back surface field of silicon nanowire cells has been developed.This thesis includes major two sections as follows:?1?Three n-type heterojunction silicon nanowire?SiNWs?solar cells were prepared based on transparent transition metal oxide?TMO?films?V₂O₅,MoO₃,WO₃ and TiO₂?.The structure of the cell is ITO/TMO/n-SiNWs/TiO₂/Al heterojunction structure,where V₂O₅,MoO₃,and WO₃ were used as hole transport layersand TiO₂ was used as an electron transport layer.We mainly studied the effects of the length of nanowires,the compositon and the quality of V₂O₅ films,and the defects on the performance of V₂O₅heterojunction silicon nanowire cells.A power conversion efficiency of 12.7%V₂O₅heterojunction silicon nanowire solar cellwith alength of 1.45mm has been successfully prepared.The high efficiency of silicon nanowire solar cells can be contributed to the excellent light-harvesting effect of nanowire array,the carrier-selective transmission properties of the V₂O₅ layer and the TiO₂ layer,and the large built-in electric fields between the interface of V₂O₅ and n-Si?0.75 V obtainedvia C-V characteristic measurement?.It means that silicon nanowire solar cellswith a large open circuit voltage can be realized by the approach.The efficiency loss mainly comes from the recombination of the dingling bonddefects on the surface of the silicon nanowires.It is believe that solving this problem can improve the efficiency of the silicon nanowire solar cellsand help accelation the industrializan.?2?Transparent transition metal oxide films?V₂O₅,MoO₃ and WO₃?were used to passivate the back electrode interface between silicon and aluminum of the traditional aluminum back-silicon nanowire solar cells.Three silicon nanowires?SiNWs?solar cells were successfully prepared with the structure of ITO/N⁺/P-SiNWs/TMO/Ni/Al,where V₂O₅,MoO₃,and WO₃ were used as hole transport layers to passivate the back interface of the SiNW cell.In this thesis,the performance changes of silicon nanowire cells after passivation with three transition metal oxides were investigated and compared the performance to that of unpassivated silicon nanowire cells,which was used as a reference solar cell.Owing to the excellent passivation properties of the transition metal oxide,the performance of silicon nanowire cells achieved an 8%increase in open circuit voltage and 3%increase in conversion efficiency by passivating1.75mm silicon nanowires with MoO₃ thin films.Compared with the traditional passivation methods using high-temperature annealing of back electrode or organic compound passivation of back field,the inorganic compound passivationapproach is simple method since high temperature annealing is not requiredand the obtainedsolar cellsare stable for a long time.It provides a new appraochfor developingcheap and highefficient silicon nanowire solar cells.