Revealing the internal luminescence quantum efficiency of perovskite films via accurate quantification of photon recycling

Abstract

The internal luminescence quantum efficiency (Q lum i ) provides an excellent assessment of the optoelectronic quality of semiconductors. To determine Q lum i from the experimentally accessible external luminescence quantum efficiency (Q lum e ), it is essential to account for photon recycling, and this requires knowledge of the photon escape probability (p e ). Here, we establish an analysis procedure based on a curve-fitting model that accurately determines p e of perovskite films from photoluminescence (PL) spectra measured with a confocal microscope and an integrating sphere setup. We show that scattering-induced outcoupling of initially trapped PL explains commonly observed red-shifted and broadened PL spectral shapes and leads to p e being more than a factor of two higher compared with earlier assumptions. Applying our model to CH 3 NH 3 PbI 3 films with exceptionally high Q lum e up to 47.4% corrects previous estimates for Q lum i of $90% to a real benchmark of 78.0% G 0.5%. Thereby, our study reveals there is beyond a factor of two more scope for reducing non-radiative recombination in perovskite films than previously thought.

Small grains as recombination hot spots in perovskite solar cells

“…This is also in agreement with recent re-evaluation of the bulk recombination in perovskite thin films, which suggests it has been underestimated to date. 78 Secondly, the functionality extracted from these transport and geometry considerations is in good agreement with the extracted density of defects (Figure 6C, dashed line), strengthening our assignment of these bulk defects to be present at the grain boundaries. We emphasize that our simple model does not-and in fact, cannot-account for the rich and complex physics of interfaces between grains, yet it does offer a general insight regarding their role in determining device performance.…”

Two birds with one stone: dual grain-boundary and interface passivation enables >22% efficient inverted methylammonium-free perovskite solar cells

“…[114][115][116][117] To quantify the reduction of non-radiative recombination, PLQY measurements along with the internal quasi-Fermi level splitting (E F ), that are attributed to the 'implied V OC ' via V OC_imp = WE F /q = V OC_rad + k B T/q ln(PLQY), are discussed next. 34,118 Analysing PLQY and V OC_imp for the stack ITO/2PACz/perovskite without C 60 allows identification of whether non-radiative recombination at the HTL/perovskite limits the V OC of our PSCs. 34,35,39 For the Ref films, we find an already very high average PLQY (V OC_imp ) of 7.2% (1.206 V) which only slightly increases to 7.9% (1.218 V), 9.8% (1.218 V) and 9.7% (1.225 V) for GBP, SP and GBP&SP films, respectively (Fig.…”

Tetrafluoroborate‐Induced Reduction in Defect Density in Hybrid Perovskites through Halide Management

“…[ 41,43,44 ] By calculating an emitted photon escape probability of 8% for our MAPbI 3 thin films (see Section S1, Supporting Information), we estimate that the internal PLQE increases from (5.7 ± 1.5)% to (59.9 ± 3.9)% upon post‐treatment. Even when including recent reports of photon recycling probabilities as high as 25% [ 45 ] in MAPbI 3 films of similar thickness, the internal PLQE values would be ≈2% and ≈32% in the control and treated films, respectively. We note that we do not see an appreciable effect of the treatment on higher‐order Auger recombination, which is primarily relevant at high excitation densities (Figure S10, Supporting Information).…”