) which will be referred to as the domain size when comparing different polymer films. We also find that the radius of gyration determined from using the cylinder model (Table ) matches well with the radius of gyration obtained from a shape independent Guinier model (Table ) which has been used in other studies for analyzing RSoXS data . The Guinier model fitted plots are summarized in Fig. and the obtained radius of gyration values are tabulated in Table . It is important to note here that the Guinier model for the PM7 blend film printed at room temperature could only fit the lower Q region which corresponds to the large domains, whereas the cylinder model can describe the two populations at this condition. When the coating temperature increases to 105 °C, the PM7 blend film exhibits small domains with a radius of gyration of 13.1 nm which is reduced by ~ 40% as compared to PM7 blend films printed at 25 °C, while the domain sizes of PM7 D1 and D2 remained relatively stable as shown in Fig. . The Lorentz corrected intensity profiles of the PM7 blend films in Fig. illustrates this shift more clearly as indicated by the arrow. Furthermore, the integration of these Lorentz corrected curves normalized with the total illuminated volume gives the total scattering intensity which can be used to determine the relative domain purity. Based on this approach, the relative domain purity of the three blend films printed at low and high temperatures are thus calculated and compared in Fig. . We observe an increased domain purity for PM7 and PM7 D1 at a high coating temperature, but no substantial change is observed for PM7 D2. Therefore, we cannot generalize the effect of temperature on the domain purity. Nevertheless, we find that domain size is highly correlated with the aggregate structures of the three polymers discussed previously. To correlate the solution aggregate structures and the blend film morphology to the device performance of OSCs, we carried out device fabrication using substrate temperatures of 25 °C, 65 °C, and 105 °C from a room temperature solution. At each coating temperature, we retained the coating speed at 5 mm/s and varied the blade angle as discussed previously to achieve uniform films with optimal thickness of ~ 80 nm. The J-V performance of inverted geometry devices with an ITO/ZnO/active layer/MoO3/Ag architecture in which ITO acts as an electron collecting electrode (anode) and Ag as the hole collecting electrode (cathode) is shown in Figs . In Fig. , we observe that the PM7:ITIC-4F device performance changes substantially with increasing coating temperature, showing ~ 50% increase in the PCE from 5.8% to 8.7% when PM7 converted from fiber aggregates to network aggregates in solution upon heating. In comparison, the PCEs of the PM7 D1 and D2 based devices exhibited less statistical variation with only about ~ 10% and ~ 15% increase with increasing temperature respectively. This drastic device performance change in the PM7 based devices with increasing coating temperature is mainly attributed to the short circuit current (JSC) and fill factor (FF) improvement (Table , Fig. and) which are highly correlated with the morphology of the blend films. At low coating temperature, the PM7 blend film morphology exhibits large domains where polymers are oriented isotropic while PM7 D1 and D2 form small domains where polymers are oriented predominantly face-on. This morphology difference correlates well with the inferior JSC and FF of the PM7 polymer-based devices fabricated at low coating temperature as the charge generation and transport are reduced due to the large domains and the unfavorable molecular orientation. When the coating temperature is increased, we observe a significant change in the device performance of PM7 which also corresponds to the morphology change observed in the solid-state, more specifically, the domain size reduction and enhancement of the face-on molecular orientation. For PM7 D1 and D2 based devices, the device performance resiliency is also correlated with their robust solid-state morphology which is less sensitive to the processing temperature. is 20 mg/mL for the polymer and acceptor, and the coating speed is maintained at 5 mm/s at all conditions. The blade angle is varied to optimize the thickness for all films ~ 80 nm.