Making silicon solar cells in a green, low-hazardous, and inexpensive way

A facile, green, and low-cost process for fabricating silicon solar cells safely at home or in school is presented. In the process, we not only prepare a H3PO4-based nontoxic spin-on diffusion source, but also replace the hazardous HF with KOH for removal of the residual silica glass after diffusion. Furthermore, for enhancing the efficiency of solar cells, we employ a simple and low toxic sol-gel method to fabricate the TiO2 antireflection layer on the solar cell. Experimental results show that KOH not only effectively removes residual silica glass, it also etches back the dead layer, resulting in the reduced minority carrier recombination. However, as KOH can also etch away silicon, care should be taken to prevent over-etching of the silicon that damages the p-n junction. Si solar cells prepared with our approach reach 12.1% in efficiency. To test if our HF-free process also works on an optimized production process, we test our KOH etching step in an optimized solar cell process in a production line. An averaged cell efficiency of 17.5% was attained, which is comparable to that of 17.8% with cells fabricated in the traditional production process employing HF etching. This fact evidences the future potential of producing HF-free green solar cells.