  Photochemical upconversion is a promising way to boost the efficiency of
solar cells using triplet exciton annihilation. Currently, predicting the
performance of photochemical upconversion devices is challenging. We present an
open source software package which takes experimental parameters as inputs and
gives the figure of merit of an upconversion system, enabling theory-driven
design of better solar energy devices. We incorporate the statistical
distribution of triplet excitons between the sensitizer and the emitter. Using
the dynamic quenching effect of the sensitizer on emitter triplet excitons, we
show that the optimal sensitizer concentration can be below the sensitizer
solubility limit in liquid devices. These theoretical contributions can
explain, without use of heavy atom-induced triplet exciton formation or phenyl
group rotation, the experimental failure of zinc octaethylporphyrin to
effectively sensitize diphenylanthracene, where platinum octaethylporphyrin
succeeds. Our predictions indicate a change in direction for device design that
will reduce triplet exciton losses.
