A wide-bandgap polymer based on the alkylphenyl-substituted benzo[1,2-b:4,5-b′]dithiophene unit with high power conversion efficiency of over 11%

Abstract

A novel wide-bandgap conjugated polymer (PTZP) based on alkylphenyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-P) as the electron-rich unit and thiazolo[5,4-d]thiazole (TTz) as the electron-deficient unit was designed and synthesized for the non-fullerene polymer solar cell (PSCs) application. The polymer exhibited a wide bandgap of 2.01 eV with a strong absorption in the range of 300–620 nm, which was complementary with that of the fused-ring small molecule acceptor (SMA; 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile, IDIC). Also, the polymer exhibits a deep highest occupied molecular orbital (HOMO) energy level of −5.41 eV. Furthermore, the polymer film possesses strong crystallinity and dominated face-on stacking with a small d-spacing of 3.65 Å, resulting in a high hole mobility of 4.01 × 10⁻³ cm² V⁻¹ s⁻¹. The optimal PSCs based on the PTZP:IDIC blend showed a high PCE of 11.8% with an open-circuit voltage (V_oc) of 0.90 V, a short-circuit current density (J_sc) of 17.9 mA cm⁻² and a fill factor (FF) of 73.3%. Moreover, the device with an active layer thickness of up to 200 nm or area of up to 0.81 cm² exhibited outstanding performance, with PCE of over 10%, resulting from the excellent molecular stacking. These results revealed that PTZP will be a promising conjugated polymer for the fabrication of efficient large-area PSCs.