Is Disorder Beneficial in Perovskite-Sensitized Solid-State Upconversion? The Role of DBP Doping in Rubrene

Abstract

Solid-state bulk lead halide perovskite thin films have recently shown progress as triplet sensitizers in infrared-to-visible photon upconversion (UC) schemes. Common systems pair lead halide perovskites with a rubrene annihilator, doped with ∼1% dibenzotetraphenylperiflanthene (DBP), to prevent the efficiency limiting process of singlet fission. However, the interplay between rubrene and DBP has not been investigated in these spin-coated bilayer systems. Here, we investigate the UC photoluminescence intensity and the dynamics of the triplet sensitization process as a function of the DBP doping percentage of rubrene, finding that, as a whole, DBP does not significantly affect the UC intensity of the lead halide perovskite sensitized scheme. This indicates that, in the solution-processed devices reported here, rubrene disorder is sufficient to suppress unwanted singlet fission processes, removing the requirement of an annihilator/emitter system.

Interfacial Trap‐Assisted Triplet Generation in Lead Halide Perovskite Sensitized Solid‐State Upconversion

“…The perovskite PL dynamics in upconversion devices is also power‐dependent, consistent with previous literatures on similar perovskite/Rub:DBP systems. [ 12,20,21,32 ] All three devices (Figure 4c–e) present similar trends with less efficient PL quenching at higher incident power. This power dependence difference is likely due to both competition with bulk carrier recombination and charge accumulation at the perovskite/rubrene interface that can lead to triplet‐charge annihilation (TCA).…”

Mixed halide bulk perovskite triplet sensitizers: Interplay between band alignment, mid-gap traps, and phonons

“…The bilayer UC devices consist of a ~100 nm thin perovskite film based on FA0.85MA0.15Pb(I1-xBrx)3 (x = 0 -0.15) onto which the rubrene annihilator layer doped with ~1% dibenzotetraphenylperiflanthene (DBP) is spin coated. 27 We find that small amounts of bromide increase the native perovskite PL quantum yield and lifetime, which result in an increased UC yield, due to the competition between interfacial carrier trapping and charge transfer to rubrene. 26 Interestingly, we find that even sub-bandgap photons can be absorbed and subsequently upconverted, indicating the possible role of mid-gap trap states and thermal excitation to the band edge by the rich phonon bath in perovskites on the UC process.…”

In optimized rubrene-based nanoparticle blends for photon upconversion, singlet energy collection outcompetes triplet-pair separation, not singlet fission

“…This is because the singlet states populated by TTA can undergo the reverse process of singlet fission, 23,24 whereby they split into pairs of triplet excitons, rather than emitting their energy radiatively. 18,[25][26][27][28] As a result, several strategies have recently been reported to mitigate the effects of singlet fission in solid rubrene-based TTA-UC systems. The addition of bulky side groups to increase intermolecular distances has been shown to improve the PLQY of rubrene several-fold, 26,29,30 though the benefit to TTA-UC is severely tempered by reduced triplet diffusivity.…”