21020
We demonstrated the fabrication of inverted CdSe / CdS / ZnS quantum dot light emitting devices ( QD - LEDs ) using titanium dioxide ( TiO2 ) as an electron - injection layer and investigated the operating mechanism by utilizing different hole - transport materials , 4 , 4 - N , N - dicarbazole - biphenyl ( CBP ) and 4 , 4 ' , 4 ' ' - tris ( carbazol - 9 - yl ) - triphenylamine ( TCTA ) .
 CdSe, CdS, ZnS, titanium dioxide, TiO2, 4 , 4 - N , N - dicarbazole - biphenyl, CBP, 4 , 4 ' , 4 ' ' - tris ( carbazol - 9 - yl ) - triphenylamine, TCTA
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 CdSe, CdS, ZnS, titanium dioxide, TiO2, 4 , 4 - N , N - dicarbazole - biphenyl, CBP, 4 , 4 ' , 4 ' ' - tris ( carbazol - 9 - yl ) - triphenylamine, TCTA