8470
Through controlled fabrication , high - to low - density nanohybrid networks are achieved , with low - density hybrid carbon nanotube networks tested as hole transport layers ( HTLs ) for bulk heterojunction ( BHJ ) organic photovoltaics ( OPV ) .
 carbon
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 carbon