Plasmon-Enhanced Charge Transport Processes for Improved Collection of Photo-Current in Polymer Solar Cells

Silver sulfide (Ag2S) nanoparticles were incorporated into the electron transport layer (ETL) of thin-film organic photovoltaic cells to assist in light trapping and improve charge-transport processes. The solar cells were fabricated in an inverted device architecture design using a solar absorber composed of donor polymer poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b; 4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) and the non-fullerene acceptor (NFA) 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(5-hexylthienyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC-Th). The Ag2S nanoparticles were dispersed in the zinc oxide nano-ink suspension, at varying concentrations from 0.00 to 0.55% by weight, to be able to determine the optimum doping level for the best solar cell performances. The nanoparticles exhibit local surface plasmon resonance absorption and produce intense local electric field in the polymer matrix, which is beneficial to efficient exciton dissociation. Consequently, improved device performances were recorded at various effective device areas. The measured electrical and optical properties of the NP-doped polymer films showed improved characteristics for energy harvesting. This investigation demonstrates the effective collection of photo-generated charges using Ag2S nanoparticle-doped ETLs in NFA-based thin-film organic solar cells.