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Triplet-triplet annihilation-based photon upconversion (UC) using bulk perovskite sensitizers has been previously shown to facilitate efficient UC at low fluences. However, the fabrication of the UC devices has not been fully optimized; thus, there is room for improvement. Here, we apply techniques that have been successful in enhancing the performance of perovskite solar cells in order to also improve perovskite-sensitized UC devices. In particular, we investigate the use of a post-fabrication thermal annealing step, overstoichiometric vs stoichiometric addition of PbI2 to the perovskite precursors, methylammonium vs formamidinium cation-rich lead halide perovskite compositions, and the use of different solvents for the annihilator molecules on the perovskite/annihilator interface. We find that excess PbI2 does not significantly affect the UC process, while the perovskite composition is crucial for the yield of extracted carriers across the interface. Comparing toluene and chlorobenzene, we find that the solvent used to deposit the annihilator is also a key factor in the overall device performance. Moreover, we find that thermal annealing of the whole device architecture significantly improves the UC performance by a factor of three.

Photon upconversion, particularly via triplet–triplet annihilation (TTA), could prove beneficial in expanding the efficiencies and overall impacts of optoelectronic devices across a multitude of technologies. The recent development of bulk metal halide perovskites as triplet sensitizers is one potential step toward the industrialization of upconversion-enabled devices. Here, we investigate the impact of varying additions of bromide into a lead iodide perovskite thin film on the TTA upconversion process in the annihilator molecule rubrene. We find an interplay between the bromide content and the overall device efficiency. In particular, a higher bromide content results in higher internal upconversion efficiencies enabled by more efficient charge extraction at the interface likely due to a more favorable band alignment. However, the external upconversion efficiency decreases as the absorption cross section in the near infrared is reduced. The highest upconversion performance is found in our study for a bromide content of 5%. This result can be traced back to a high absorption cross section in the near infrared and higher photoluminescence quantum yield in comparison to the iodide-only perovskite and an increased driving force for charge transfer.