Molecular ferroelectrics, characterized by outstanding photoelectric and unique ferroelectric properties, invigorate the field of ferroelectric photovoltaics. Nonetheless, the performance of molecular ferroelectric devices is hindered by fine grains resulting from poor high-temperature stability. In this work, we successfully achieved micron-grained molecular ferroelectric films by using the space-confined vapor deposited method. The optimized film exhibited a significant increase in grain size from the nanometer level (0.08 µm) to the micrometer level (~ 2 µm), leading to improved optoelectronic and ferroelectricity. Furthermore, it optimizes the energy level and enhances the photovoltaic performance of vertical devices. Research on the mechanism shows that high annealing temperature and inhibiting component loss play an important role in obtaining large grain films. This work provides new research ideas for improving the quality of molecular ferroelectric films and provides valuable reference for the fabrication of high performance molecular ferroelectric photovoltaic devices.