Wide voltage range comparator (with zener diode)
You can improve the sharpness by just moving the parts around a bit. The base current
doesn't exceed about 30mA in the below circuit, which is acceptable. 







simulate this circuit &ndash; Schematic created using CircuitLab



But really, as @Tim suggests, you'd be better off using a comparator and some kind of reference. For one thing, you could easily get tolerance of 1% or better, whereas the zener alone has +/- 5% tolerance.