That's a thin-film bolometer, similar in general character to the ones
used in modern uncooled microbolometer cameras. Compared with
visible/NIR photodiodes, they're slow and very insensitive, but they
sure do have a wide wavelength range.
20 years ago I built an interesting system called "Footprints" that I've
discussed here a few times over the years. It used an array of 96
carbon-ink pixels screen-printed on a 9-um thick free-standing film of
PVDF (which is basically fluorinated Saran Wrap). The pixels were 3 x 5
mm on a 6-mm pitch, to leave room for the wiring. The readout
multiplexer was a single red display LED per pixel.
Diodes ideally conduct in only one direction. The particular LEDs I
used leaked less than 50 fA between -5V and +0.5V bias. Interfacing
them to an AC-only sensor such as a pyoelectric requires a bit of bias
current, which in my gizmo was supplied by four green display LEDs,
which allowed the processor to adjust the average bias current between 0
and about 5 pA per LED.
The optical system was a moulded Fresnel lens made out of HDPE
(bleach-bottle plastic).
When it was done, it had very competitive sensitivity: noise equivalent
delta-T of just over 0.1 K, not bad for something so minimalistic.
We tried licensing it, but couldn't because the parts cost was too low.