## 3 Results and Discussion
### Electrochemical and Photovoltaic Properties of DVB-T-ID Osm
Figure 4: Cyclic voltammetry and molecular structure of a DVB-T-ID thin film in 0.1 M TBAPF\({}_{6}\) as the supporting electrolyte in an anhydrous acetonitrile solution, with ferrocene as an external reference. To explore the morphological behavior of the blend films, AFM measurements of DVB-T-ID:PC\({}_{61}\)BM thin films in tapping mode were performed. Figure 6 presents the AFM images of DVB-T-ID:PC\({}_{61}\)BM thin films with different blend ratios. With a blend ratio of 1:2, _w/w_, the DVB- T-ID:PC\({}_{61}\)BM thin film displays smooth and uniform morphology, exhibiting small grains at a nanoscale level, as shown in Figure 6c. In addition, the height and 3D images of the DVB-T-ID:PC\({}_{61}\)BM (1:2, _w/w_) thin film again confirm the smooth surface, which might be a consequence of the well-mixed donor-acceptor in blend form, leading to favorable interpenetrating networks with an appropriate degree of phase separation and a high charge carrier extraction [39]. A low root-mean-square roughness (R\({}_{\text{rms}}\)) value of \(\sim\)4.37 nm was estimated for the DVB-T-ID:PC\({}_{61}\)BM (1:2, _w/w_) thin film, whereas other blend ratios presented high R\({}_{\text{rms}}\) values. The blend film roughness is basically controlled with the amount of the PC\({}_{61}\)BM acceptor in the blend film. Herein, further increments of the PC\({}_{61}\)BM acceptor (1:3, _w/w_) lead to the formation of large aggregates. Large aggregates in a DVB-T-ID:PC\({}_{61}\)BM (1:3, _w/w_) thin film might prevent an immediate charge separation, which is also supported by PL quenching in (1:3, _w/_w_) and thus results in poor photovoltaic performances. Moreover, a high FF of BHJ-OSCs might due to good surface smoothness, uniform grain sizes and low surface roughness [40], which might result in a fast charge extraction. Therefore, the optimal active layer of DVB-T-ID:PC\({}_{61}\)BM (1:2, _w/w_) evidences the good miscibility of DVB-T-ID and PC\({}_{61}\)BM, which might be helpful in forming a bi-continuous network structure through quick phase segregation. This phenomenon promotes the proper charge carrier collection for BHJ solar cell devices, resulting in a high photocurrent and a high PCE. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Active Layer** & **V\({}_{\text{oc}}\) (V)** & **J\({}_{\text{sc}}\) (mA/cm\({}^{2}\))** & **FF** & **PCE (\%)** & **Ref.** \\ \hline \hline OIYM(4):PC\({}_{61}\)BM & 0.74 & 6.65 & 0.47 & 2.34 & [41] \\ DDIN7T:PC\({}_{61}\)BM & 0.76 & 3.14 & 0.28 & 0.66 & [42] \\ D2R(8+2)7T:PC\({}_{61}\)BM & 0.92 & 6.77 & 0.39 & 2.46 & [43] \\ DTIDTQX:C\({}_{70}\) & 0.71 & 6.24 & 0.38 & 1.70 & [44] \\ DINCNDTPS:PC\({}_{71}\)BM & 0.86 & 1.82 & 0.37 & 0.58 & [45] \\ InTTID:PC\({}_{61}\)BM & 0.71 & 2.69 & 0.32 & 0.62 & [30] \\ InCNTTID:PC\({}_{61}\)BM & 0.82 & 3.95 & 0.38 & 1.22 & [30] \\ DVB-T-ID:PC\({}_{61}\)BM & (11, _w/w_) & 0.634 & 8.85 & 0.46 & 2.57 & This work \\ DVB-T-ID:PC\({}_{61}\)BM & & & & & \\ (1:2, _w/w_) & 0.637 & 10.63 & 0.48 & 3.10 & This work \\ DVB-T-ID:PC\({}_{61}\)BM & & & & & \\ (1:3, _w/w_) & 0.647 & 6.39 & 0.45 & 1.86 & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of photovoltaic parameters of the fabricated and reported BHJ-OSCs. Figure 5: (**a**) Band structure of BHJ-OSC and (**b**) J-V curves of fabricated BHJ-OSCs with an active layer of DVB-T-ID:PC\({}_{61}\)BM of blend ratios 1:1 and 1:2 (_w/w_).