Thick Film Polymer Solar Cells Based on Naphtho[1,2‐c:5,6‐c]bis[1,2,5]thiadiazole Conjugated Polymers with Efficiency over 11%

Two novel narrow bandgap π-conjugated polymers based on naphtho[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (NT) unit are developed, which contain the thiophene or benzodithiophene flanked with alkylthiophene as the electron-donating segment. Both copolymers exhibit strong aggregations both in solution and as thin films. The resulting copolymers with higher molecular weight show higher photovoltaic performance by virtue of the enhanced short-circuit current densities and fill factors, which can be attributed to their higher absorptivity and formation of more favorable film morphologies. Polymer solar cells (PSCs) fabricated with the copolymer PNTT achieve remarkable power conversion efficiencies (PCEs) > 11% based on both conventional and inverted structures at the photoactive layer thickness of 280 nm, which is the highest value so far observed from NT-based copolymers. Of particular interest is that the device performances are insensitive to the thickness of the photoactive layer, for which the PCEs > 10% can be achieved with film thickness ranging from 150 to 660 nm, and the PCE remains >9% at the thickness over 1 µm. These findings demonstrate that these NT-based copolymers can be promising candidates for the construction of thick film PSCs toward low-cost roll-to-roll processing technology.