Room temperature processed polymers for high-efficient polymer solar cells with power conversion efficiency over 9%

Although the family of difluoro-2,1,3-benzothiadiazole with 2-octyldodecyl alkyl chains based donor copolymers have reached over 10% power conversion efficiencies (PCE) in past three years, several limitations are holding back their further commercialization application. For instance, those polymers have to be processed at a high temperature (~110 °C) due to their strong aggregation in the solution. Here we report the achievement of low temperature-processed polymers for high-efficient polymer solar cells (PSCs) via random polymerization. The introduction of 2,2′-(perfluoro-1,4-phenylene)dithiophene (2TPF4) via random polymerization can weaken the strong self-aggregation of the polymers, enabling the polymers processible by spin-coating at room temperature as well as favor the formation of a near ideal active layer morphology which involves highly crystalline yet with reasonably small polymer domains. All these three polymers exhibit preferable face-on orientation and the domain purity could be significantly changed by the introduction of 2TPF4 block. A superior PCE of 9.4% of the photovoltaic device based on PffBT-2TPF4-9/1 was obtained, which is one of the best values for room temperature-processed solar cells. These findings indicate that low temperature processed high-efficient PSCs can be achieved by rational conjugated backbone engineering, which presents distinctive advantages for largescale production in the near future.