Organic Photovoltaics Utilizing a Polymer Nanofiber/Fullerene Interdigitated Bilayer Prepared by Sequential Solution Deposition

Organic photovoltaics (OPVs) utilizing an interdigitated bilayer of an alkoxynaphthalene-based polymer nanofiber/fullerene have been developed by the sequential solution deposition (SqD) process. Spin-coating a polymer solution incorporated with 1-chloronaphthalene (1-CN) results in the formation of dense polymer nanofibers with diameters of 30-50 nm. The fullerene top layer is sequentially deposited onto the polymer nanofiber bottom layer to form a bulk heterojunction (BHJ) through the interdiffusion of fullerene. Compared to a plane polymer bottom layer, the preformed polymer nanofiber bottom layer provides effective interdiffusion of phenyl-C₇₁-butyric acid methyl ester (PCBM) by facilitating the fast swelling of the PCBM solvent into the polymer bottom layer. The SqD processed OPV utilizing a polymer nanofiber/fullerene bilayer exhibits higher photocurrent density compared to those utilizing a plane polymer layer/fullerene bilayer. Furthermore, the SqD OPV exhibited superior solar cell performance to the OPV prepared by the polymer:fullerene blend solution deposition (BSD) process. Optical, morphological, and J-V investigations on the photoactive layers reveal that improved ordering of the polymer chain with proper direction and increased heterojunction area are the main contributors to the superior solar cell performance. These results suggest an efficient interdigitated BHJ morphology can be realized by a sequentially deposited, preformed nanofiber/fullerene bilayer without a thermal annealing process.