  CUPID is a next-generation neutrinoless double-beta decay experiment that
will require cryogenic light detectors to improve background suppression, via
the simultaneous readout of heat and light channels from its scintillating
crystals. In this work we showcase light detectors based on a novel Ir-Pt
bilayer transition edge sensor. We have performed a systematic study to improve
the thermal coupling between the photon absorber and the sensor, and thereby
its responsivity. Our first devices meet CUPID's baseline noise requirement of
<100~eV rms. Our detectors have risetimes of $\sim$180 $\mu$s and measured
timing jitter of <20 $\mu$s for the expected signal-to-noise at the Q-value of
the decay, which achieves the CUPID's criterion of rejecting two-neutrino
double-beta decay pileup events. The current work will inform the fabrication
of future devices, culminating in the final TES design and a scaleable readout
scheme for CUPID.
