13891
This model also indicates that bimolecular recombination is the dominant charge recombination mechanism at 20 wt % PCBM and above .
 Chemical: PCBM
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: PCBM