Over the past few years, high external quantum efficiencies (EQE) have been achieved for blue, green, red, and near infrared perovskite light-emitting diodes (PeLEDs), and their energy efficiencies are approaching the efficiencies of III-V based LEDs. Beyond the visible regime, ultraviolet light offers great promise for many applications such as disinfection, which has become increasingly important since the COVID-19 pandemic. However, PeLEDs demonstrate poor performance in the violet/ultraviolet region, with reports of violet PeLED performance hindered by poor thin film quality. In this work, we improve the uniformity of perovskite film by adding water into the precursor solution to engineer the crystallization process of spin-coated 2D perovskite. The PeLEDs deliver bright violet emission at 408 nm, with a maximum external quantum efficiency of 0.41%, a fivefold increase over control devices. This work demonstrates viable steps towards cost-effective, efficient ultraviolet PeLEDs.