Ultrafast Charge Generation Enhancement in Nanoscale Polymer Solar Cells with DIO Additive

• Main Authors: Tongchao Shi, Zeyu Zhang, Xia Guo, Zhengzheng Liu, Chunwei Wang, Sihao Huang, Tingyuan Jia, Chenjing Quan, Qian Xiong, Maojie Zhang, Juan Du, Yuxin Leng
• Format: Article
• Language: English
• Published: MDPI AG 2020-10-01
• Series: Nanomaterials
• Subjects: nanoscale polymer solar cells; DIO additive; transient absorption spectroscopy
• Online Access: https://www.mdpi.com/2079-4991/10/11/2174

We study the ultrafast photoexcitation dynamics in PBDTTT-C-T (P51, poly(4,8-bis(5-(2-ethylhexyl)-thiophene-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-<i>alt</i>-alkylcarbonyl-thieno[3,4-<i>b</i>]thiophene)) film (~100 nm thickness) and PBDTTT-C-T:PC₇₁BM (P51:PC₇₁BM, phenyl-C₇₁-butyric-acid-methyl ester) nanostructured blend (∼100 nm thickness) with/without DIO(1,8-diiodooctane) additives with sub-10 fs transient absorption (TA). It is revealed that hot-exciton dissociation and vibrational relaxation could occur in P51 with a lifetime of ~160 fs and was hardly affected by DIO. However, the introduction of DIO in P51 brings a longer lifetime of polaron pairs, which could make a contribution to photocarrier generation. In P51:PC₇₁BM nanostructured blends, DIO could promote the Charge Transfer (CT) excitons and free charges generation with a ~5% increasement in ~100 fs. Moreover, the dissociation of CT excitons is faster with DIO, showing a ~5% growth within 1 ps. The promotion of CT excitons and free charge generation by DIO additive is closely related with active layer nanomorphology, accounting for J_sc enhancement. These results reveal the effect of DIO on carrier generation and separation, providing an effective route to improve the efficiency of nanoscale polymer solar cells.