Suboptimal audio quality, but it introduces a non-silicon crystalline solution:
Graphene offers better cost and performance than Indium Tin Oxide. A product is offered but
the promotion looks a little sketchy
This just uses 'transparent carbon' as a conductive layer. Research is ongoing with 2D molecules of various elements, sheets oriented at 'magic angles', and sandwiched with other molecules held between two layers -- all offer possibilites that are myriad.
OTOH DIY graphene solar reflectors: