  We explore the application of excitation correlation spectroscopy to detect
nonlinear photophysical dynamics in two distinct semiconductor classes through
time-integrated photoluminescence and photocurrent measurements. In this
experiment, two variably delayed femtosecond pulses excite the semiconductor,
and the time-integrated photoluminescence or photocurrent component arising
from the nonlinear dynamics of the populations induced by each pulse is
measured as a function of inter-pulse delay by phase-sensitive detection with a
lock-in amplifier. We focus on two limiting materials systems with contrasting
optical properties: a prototypical lead-halide perovskite (LHP) solar cell, in
which primary photoexcitations are charge photocarriers, and a single-component
organic-semiconductor diode, which features Frenkel excitons as primary
photoexcitations. The photoexcitation dynamics perceived by the two detection
schemes in these contrasting systems are distinct. Nonlinear-dynamic
contributions in the photoluminescence detection scheme arise from
contributions to radiative recombination in both materials systems, while
photocurrent arises directly in the LHP but indirectly following exciton
dissociation in the organic system. Consequently, the basic photophysics of the
two systems are reflected differently when comparing measurements with the two
detection schemes.
