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Crystalline Si photovoltaic modules still have high production cost due to significant consumption of the Si wafer. Reducing the large amount of Si material consumption is thus a critical issue. Here we deve lop a two-step metal-assisted etching technique for forming vertically-aligned Si nanohole thin films from bulk Si wafers. The formation of Si nanohole thin films includes a series of solution processes: deposition of Ag nanoparticles in an AgNO 3 / HF aqueous solution, formation of Si nanohole arrays at the first-step metal-assisted etching, and side etching of the roots of the nanohole structure at the second-step meta l-assisted etching. All th e processes can proceed at around room temperature. A Si nanohole thin film with an averag e hole-size of 100 nm and a thickness of 5 m-20 m was hence formed at the top of the wafer. Afterwards, the Si nanohole thin film was tran sferred onto alien substrates. The Si nanohole thin film has the crystal quality similar to the bulk Si wafer. The above bul k Si substrate can be reused. With similar processes, other Si nanohole thin films can be formed fr om the above recycled Si wafer. The hole size and thickness are similar. The Si wafers recycled will significan tly reduce the material consumption of Si. Thus, such technique is promising for lowering the cost of Si solar cells. Keywords: Si nanohole, metal-assisted etching, transfer, lithium battery anode, Si nanohole powder, photovoltaic, Si wafer recycling.