Toward Efficient Polymer Solar Cells Processed by a Solution-Processed Layer-By-Layer Approach.

The solution-processed layer-by-layer (LBL) method has potential to achieve high-performance polymer solar cells (PSCs) due to its advantage of enriching donors near the anode and acceptors near the cathode. However, power conversion efficiencies (PCEs) of the LBL-PSCs are still significantly lower than those of conventional one-step-processed PSCs (OS-PSCs). A method to solve the critical problems in LBL-PSCs is reported here. By employing a specific mixed solvent (o-dichlorobenzene [o-DCB]/tetrahydrofuran) to spin-coat the small-molecular acceptor IT-4F onto a layer of the newly designed polymer donor (PBDB-TFS1), appropriate interdiffusion between the PBDB-TFS1 and the IT-4F can critically be controlled, and then an ideal phase separation of the active layer and large donor/acceptor interface area can be realized with a certain amount of o-DCB. The PSCs based on the LBL method exhibit PCEs as high as 13.0%, higher than that of the counterpart (11.8%) made by the conventional OS solution method. This preliminary work reveals that the LBL method is a promising approach to the promotion of the photovoltaic performance of polymer solar cells.