Fig. 21. (a) Organic solar cell device structure with CQDs (C in C-CQDs indicates the carbon vapour deposition method). (b) Energy level diagram of the solar cells with CQDs as ETLs and P3HT:PC₆₁BM, PTB7:PC₆₁BM or PTB7-Th:PC₇₁BM as the active layer (This figure has been adapted/reproduced from ref. 143 with permission from Elsevier, Copyright 2016).