A facile, green, and low-cost process for fabricating high efficient silicon solar cells safely at home or in school in an aim to break the bottleneck of widespread photovoltaic usage
JIh-Shang Hwang1*, Chien-Yi Wu1, Ya-Hsien Tai1, Sian-Ren Chen1, Peng Tseng2, Surojit Chattopadhyay3, Yen-Chieh Chiu4, Shi-Wei Chen5
1Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan
2Department of Electrical Engineering, National Taiwan Ocean University, Keelung, Taiwan
3Institute of Biophotonics, National Yang-Ming University, Taipe, Taiwan
4Department of Electronic Engineering, Ming Chi University of Technology, New Taipei, Taiwan
5Photovoltaics Technology Center, Industrial Technology Research Institute, Hsinchu, Taiwan
* presenting author:Jih-Shang Hwang, email:hjsspin@mail.ntou.edu.tw
The high production cost of solar cells have long been a bottleneck of widespread photovoltaic (PV) usage. To break the bottleneck, conventional efforts made to improve the efficiency of Si solar cells would usually result in vain, for it usually requires an even more sophisticated (costly) process for the improvement. To this end, alternatively, we herein present a facile, green, and low-cost process for fabricating silicon solar cells safely at home or in school. 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. Importantly, the chemicals used in this process are all environmentally friendly, easily recycled leaving minimum or no toxic waste. For example, KOH, when mixed with phosphorous acid (H3PO3), forms potassium phosphite, which is a water soluble fertilizer widely used in controlling microbial plant diseases. Likewise, H3PO4, when reacted with NH3, can be turned into diammonium phosphate ((NH4)2HPO4), which is also a commonly used fertilizer. We believe that a variety of cottage industries could make their own powerhouse. These powerhouses would not only provide electricity for their everyday life but also power their cottage industries, enabling a wide spread usage of the PV-cells but with no environmental concerns. Dedicated small scale solar power production units can be realized with increasing density for penetrating commercial and geographical barriers presented by the rural and inaccessible areas of the country. This is especially helpful for the resource-poor people living in the tropics. The vision of widespread usage of solar power, projected several decades back, may move a step forward.

Keywords: silicon solar cell, green, KOH, HF-free, dead layer