# Photochemical Upconversion Theory: Importance of Triplet Energy Levels and Triplet Quenching

## TL;DR

This paper introduces an open source software for predicting photochemical upconversion efficiency, emphasizing the role of triplet energy levels and quenching effects, to guide the design of more effective solar energy devices.

## Contribution

It presents a theory-driven computational tool that models triplet exciton dynamics and explains experimental results without relying on heavy atom effects or molecular rotation.

## Key findings

- Optimal sensitizer concentration can be below solubility limits.
- Theoretical model explains why certain sensitizers succeed or fail.
- Predictions suggest new directions for reducing triplet exciton losses.

## Abstract

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.