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The conversion efficiency could be increased further to 6 . 2 % by increasing the thickness of the BSO film , which is one of the highest efficiencies from non - TiO 2 - based DSSCs .
 BSO, TiO 2
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 BSO, TiO 2