Solution-Processable PEDOT:PSS:α-In₂Se₃ with Enhanced Conductivity as a Hole Transport Layer for High-Performance Polymer Solar Cells

Two-dimensional (2D) nanosheets have attracted significant attention in photovoltaic devices in recent years owing to their outstanding photoelectric properties. Herein, 2D α-In2Se3 nanosheets with high conductivity and suitable work function are synthesized by liquid-phase exfoliation method. To ameliorate the low conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (2.21 × 10–3 S cm–1), α-In2Se3 nanosheets are directly added into PEDOT:PSS to obtain the PEDOT:PSS:α-In2Se3 composite film. The composite film exhibits excellent optical transmittance, suitable work function, and enhanced conductivity (1.54 × 10–2 S cm–1). To profoundly investigate the mechanism of conductivity improvement, X-ray photoelectron spectroscopy, Raman spectroscopy, electron paramagnetic resonance, and atomic force microscopy are conducted. The results show that the synergistic effect of 2D α-In2Se3 nanosheets and isopropyl alcohol/deionized water cosolvent screens the Coulombic attraction among PEDOT and PSS. The screening effect results in the partial removal of PSS and the benzoid–quinoid transition of PEDOT. In addition, α-In2Se3 nanosheets may serve as physical linkers for PEDOT chains. Both these effects are beneficial to increase the interfacial contact area between PEDOT chains and form a larger conductive network of PEDOT, leading to an enhanced conductivity. The composite film is first employed as a hole transport layer (HTL) in polymer solar cells (PSCs). The power conversion efficiency (PCE) of the poly[2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione)] (PBDB-T):3,9-bis(2-methylene(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)dithieno-[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC)-based device with composite HTL is 10% higher than that of the unmodified PBDB-T:ITIC-based device, and the maximum PCE of 15.89% is achieved in the (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene))-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione))] (PM6):(2,2′-((2Z,2Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2,″3″:4′,50]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) (Y6) system. More interestingly, the stability of devices with composite HTL is improved owing to the partial removal of PSS. Thus, the PEDOT:PSS:α-In2Se3 composite can be a potential HTL material in PSCs.