  Future space missions that aim to detect and characterize Earth-like
exoplanets will require an instrument that efficiently measures spectra of
these planets, placing strict requirements on detector performance. The
upcoming Roman Space Telescope will demonstrate the performance of an
electron-multiplying charge-coupled device (EMCCD) as part of the coronagraphic
instrument (CGI). The recent LUVOIR and HabEx studies baselined pairing such a
detector with an integral field spectrograph (IFS) to take spectra of multiple
exoplanets and debris disks simultaneously. We investigate the scientific
impact of a noiseless energy-resolving detector for the planned Habitable
Worlds Observatory's (HWO) coronagraphic instrument. By assuming higher quantum
efficiency, higher optical throughput, and zero noise, we effectively place
upper limits on the impact of advancing detector technologies. We find that
energy-resolving detectors would potentially take spectra of hundreds of
additional exoplanets "for free" over the course of an HWO survey, greatly
increasing its scientific yield.
