Characterization and properties of a modified Si solar cell emitter by a porous Si layer

Porous Si (PS) has become an interesting material owing to its potential applications in many fields including microelectronics, optoelectronics and photovoltaics. PS layers on the front surface of n+/p monocrystalline, textured Si solar cells have been investigated with the aim of improving the performance of standard screen-printed cells, because an antireflection coating and a surface passivation can be obtained simultaneously in one chemical process. The results obtained could be useful in optimising the Si surface chemical treatment process. The surface morphology and microstructure of PS layers were investigated using SEM, TEM and non-contact AFM methods. The surface morphology of a PS layer depends strongly on the region where the pores are formed. The structure of PS layer is composed of macro-pores formed in p type Si (sizes vary over a large range up to 250 nm) and meso-pores formed in the n+ region of the p–n+ junction. The meso-pores of average size 20 nm on the pyramid slope elongate preferentially along the 〈111〉 direction. The interface between the PS layer and the substrate as well as the surface roughness are clearly defined. The results show that the PS layer on the pyramids is formed uniformly along the walls. Meso-pores created on the macro-pore surface are a characteristic feature of the surface between pyramids. Such a surface modification allows improving the Si solar cell characteristics.