A New Approach for One-step Synthesis of Perovskite:fullerene Bulk Heterojunction Using Surfactant Free Microemulsion in Slot Die Method

Organometallic halide perovskite based solar cells are considered as the foundation of future photovoltaic technology. In these types of solar cells, it has been emphasized that the bulk heterojunction active layer architecture may show superior performance than the bilayer active layer architecture due to the increase in the interfacial area by intermixing both donor and acceptor phases in the bulk heterojunction. Organometallic halide perovskite with suitable acceptor in bulk heterojunction architecture can be a promising active layer in perovskite solar cells. Conventionally, the perovskite and acceptor are mixed together in a single solvent before thin film formation. Though this offers a one-step synthesis way, limited solubility of perovskite and acceptor in single solvent puts major constraint on the formation of bulk heterojunction through one-step solution processable method. This paper describes a new way of one-step synthesis of bulk heterojunction using surfactant free microemulsion in slot die method, which removes the constraint of limited solubility of the two phases in a single solvent. Emulsion of DMSO (solvent for CH3NH3PbI3) and cyclohexane (solvent for PCBM) stabilized with acetone was used for making perovskite:fullerene bulk heterojunction. Solvent evaporation dynamics has been simulated to get deeper understanding of emulsion solidification leading to bulk heterojunction formation. Structural and optical studies support the formation of bulk heterojunction for efficient charge separation at donor:acceptor interfaces. A perovskite solar cell employing this bulk heterojunction has also been reported.