## 3 Results and Discussion
The grazing incidence X-ray diffraction (GIXRD) analysis was carried out on the polymer thin films deposited on SiO\({}_{2}\) substrates (OTMS treated) by employing the same  
Figure 3: Bottom-gate bottom-contact (BGBC) OFET characteristics for **P(FDPP-TP)** polymer. (**a**) Transfer curve; (**e**) output curve; (**b**) non-annealed (room temperature) transfer curve; (**f**) non-annealed (room temperature) output curve; (**c**) transfer curve at 100 \({}^{\circ}\)C; (**g**) output curve at 150 \({}^{\circ}\)C; (**d**) transfer curve at 200 \({}^{\circ}\)C; (**h**) output curve at 200 \({}^{\circ}\)C.  
conditions applied for the fabrication of OFETs, to investigate crystallinity. The GIXRD out-of-plane patterns at different annealing temperatures are presented in Figure 4. Both annealed and non-annealed polymer thin films showed a diffraction peak of around 3.80\({}^{\circ}\) which arose from the (100) crystalline plane. However, the intensity of this peak increases gradually upon annealing to higher temperatures. Another diffraction peak can be observed around 7.25\({}^{\circ}\) upon annealing, which was not present in the non-annealed (RT) sample. This second Bragg reflection peak could be due to the (200) diffraction planes, which indicates the polymer's enhanced crystallinity upon annealing to higher temperatures, which is reflected in increased mobilities upon annealing. Apart from these two lamellar peaks, there is a broad peak around 21.10\({}^{\circ}\) in the spectra. Even though the enhancement of the peak intensity was not as dramatic as lamellar peaks, this weak diffraction indicates possible \(\pi\)-\(\pi\) stacking existing between the polymer chains that aid the carrier transport among the polymer chains. An additional (200) plane shows enhanced crystallinity which is probably due to the close polymer chain proximity from the smaller atom-size of oxygen on furan. These data indicate that greater crystallinity and more compact polymer chain packing observed from the GIXRD explain the higher hole mobility of the annealed samples, from which it can be concluded that the thermally induced crystallinity has aided in enhancing the performance of the thin-film devices. Table 1 and Figure S10 summarize the GIXRD data of the **P(FDPP-TP). **  
The channel regions of OFET devices were subjected to tapping mode atomic force microscopy (TMAFM) imaging to investigate the thin-film surface morphology. TMAFM images obtained for corresponding thin films are shown in Figure 5. \begin{table}
\begin{tabular}{c c c} \hline
**Peak** & **20 (Deg)** & **D Spacing (A\({}^{\circ}\))** \\ \hline (100) & 3.80 & 23.20 \\ (200) & 7.25 & 12.15 \\ (010) & 21.10 & 4.18 \\ \hline \end{tabular}
\end{table} 
Table 1: GIXRD data of the **P(FDPP-TP)** polymer. Figure 4: GIXRD pattern of annealed **P(FDPP-TP)** thin films at different temperatures on SiO\({}_{2}\) substrates treated with octadecyl trimethoxy silane (OTMS). The thin films prepared at room temperature showed relatively irregular small aggregated morphology, whereas the annealing induced more ordered granular structures, as shown in the annealed film phase images. For the films annealed at 150 \({}^{\circ}\)C and 200 \({}^{\circ}\)C, the phase images show fibril-like aggregates arranged in a more orderly pattern, indicating enhanced intermolecular packing in thin films, facilitating the charge transport in the semiconductor. The calculated root mean square values (RMS) for the annealed surfaces (3.37 nm, 3.88 nm, and 4.20 nm for 100 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, and 200 \({}^{\circ}\)C, respectively) also suggest that the domain size has changed with these more orderly patterns, increasing the surface roughness. The same fibrillous nature in the aggregates has been observed in high-performing semiconducting polymer thin films in literature [29, 46]. Hence, it was confirmed that the annealing had induced the fibrillary arrangement in the thin film of **P(F)DPP-TP)**, which is beneficial in the charge carrier mechanism reflected in the better device performance.