Fig. 4

Optical absorption and steady-state emission spectra of thin films. a UV-vis-NIR absorption of D-PDPP4T-HD thin films spin-coated from chloroform:1,2,4-trichlorobenzene (CF:TCB) solutions with the polymer concentration of 3 mg mL⁻¹. The characteristic peaks for the β₁ and β₂ polymorphs are indicated by purple and green frames, respectively. b Corresponding steady-state PL spectra. c A polymorph pattern is realized by locally exposing a TCB spin-coated (β₂ phase) film to chlorobenzene (CB). d Schematic illustration of the set up used to measure the polymorph pattern, where 860 nm light with a beam radius of 0.5 mm is used. e Transmitted light at 860 nm as a function of position. The red dash line (4.22 μA) indicates the current measured for bare glass without polymer film