Leveraging Bromine-Induced Large Stokes Shift in Pyrrolidinium Perovskite Nanoparticles for Improved Organic Photovoltaic Performance

Using the reverse micelle synthesis route, polystyrene-b-2vinylpyridine (PS-b-P2VP) diblock copolymers are used to synthesize hybrid perovskite nanoparticles with an ionic organic liquid five-membered heterocycle cation, pyrrolidinium (Py) (C₄H₈NH). Uniform, well-dispersed, and luminescent nanoparticles were fabricated with high stability due to the hydrophobic nature of Py and polymer encapsulation. The substitution of bromine for iodine induces a bathochromic shift, resulting in a substantial Stokes shift of 764 meV (211 nm) for mixed halide phase nanoparticles, contrary to the anticipated hypsochromic shift with bromine doping. This unique attribute of Py-based perovskites positions them as promising candidates for down-conversion applications in low-band-gap organic solar cells. Incorporating Py-based perovskite nanoparticles into bulk heterojunction organic photovoltaics (OPVs) as down-conversion layers selectively enhances the short-circuit current from UV components in the illumination source. The observed improvements in stability, uniformity, and luminescence, coupled with the distinct Stokes shift, underscore the potential of Py-based perovskite nanoparticles as a valuable component in improving the efficiency of OPVs.