Restructured porous silicon for solar photovoltaic: A review

Abstract

Abstract Bulk Silicon (Si) possesses an indirect bandgap and low surface area to volume ratio. Porous silicon (PSi), a derived material of Si, overcomes drawbacks of Si, and promises improvement in energy conversion and storage devices. However, to enhance the properties of PSi further to make it a versatile material, restructuring of PSi is helpful. Restructuring of PSi, also known as sintering, modifies the morphology, especially increases the pore diameter. The modification depends on the starting structure of pores, and the sintering parameters such as temperature (800 °C to 1250 °C), time (1 min to 2 h), and atmosphere (H2, N2, Ar, O2). Restructuring of PSi rectifies the defects and improves properties like thermal and electrical conductivity. The sintered PSi (SPSi) finds major application in reducing material cost as well as enhancing the efficiency of the solar cell. Electrochemical anodization produces a low porosity layer (LPL) (i.e., porosity 50%) in a stack on the Si substrate. High-temperature sintering converts LPL to a smooth layer and HPL to a pillar structure. For obtaining the free-standing film, the smooth layer is detached from the parent Si substrate by mechanical means. SPSi layer obtained from the layer transfer process (LTP)/epitaxial layer transfer (ELTRAN) is an excellent choice to reduce the cost of the solar cell. The PSi layer with smaller pore size can be used as a gettering layer to block the transition metal impurities from the low-quality Si substrate to high-quality epitaxially grown active Si layer. Freestanding SPSi, when used as Bragg reflector, improves the reflectivity, thereby enhancing the optical efficiency of the solar cell.