How do twisted vertically aligned nematic displays produce high contrast?

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Diagram comparing three liquid crystal phases: nematic with parallel rods aligned vertically, smectic A with rods arranged in horizontal layers, and smectic C with rods in tilted layers. — liquid crystal display Liquid crystal arrangements
In nematic arrangements the crystals are randomly positioned with all their long axes pointing in essentially the same direction, given by a vector known as the director. In smectic arrangements the crystals are further constrained to parallel planes; in smectic A the director is perpendicular to these planes, while in smectic C the director is at some other angle to the planes.

Twisted vertically aligned nematic (TVAN) displays achieve high contrast by leveraging the specific orientation of their liquid crystal molecules in response to an electric field.

In these displays, the liquid crystal molecules are characterized by a tendency to orient their long axes perpendicular to the direction of an applied electric field. To facilitate the display's operation, a small quantity of an optically active material is added to the liquid crystal. This additive causes the liquid crystal to adopt a twisted configuration when a voltage is applied. By controlling this molecular arrangement, TVAN displays are able to produce very high contrast and offer favorable viewing-angle characteristics.1