Recently the metal halide perovskite nanoparticles have attracted a lot of attention for various opto-electronic applications like micro/nano lasers, light emitting diodes, photodetectors along with solar cells due to their low fabrication costs as well as excellent electronic and optical properties.  However, dominant surface trapping continues to plague the field, despite their high defect tolerance, as evidenced by the several fold improvements in the external quantum efficiency of perovskite nanocrystals (NCs) upon appropriate surface passivation or physical confinement between high band gap materials.  In a bid towards minimizing energy loss, in this talk I introduce unique pathways to harvest additional photons via enhanced absorption and additional excitonic recombination pathways that are so far not extensively explored through doping [1] and heterostructure formation [2].

Control over the interaction of electromagnetic radiation with matter is an essential aspect for the development of efficient optoelectronic devices. A paradigmatic example of this statement can be found in the expression for the difference between the actual open circuit voltage attained from a solar cell, V_OC, and the maximum ideal one, V_OC*, which is given by:[1]

V_OC-V_OC*=k_BT ln(η_ext)       (1)

, where k_B stands for the Boltzmann constant, T for temperature and η_ext^.for the photoluminescence external quantum efficiency. It implies that reaching the Shockley-Queisser limit [2] for a single-junction solar cell requires materials that are simultaneously good light absorbers and emitters (η_ext ≈1) under open circuit conditions.

In this talk, the relevance of an adequate optical design for the new generation of devices based on lead halide perovskites will be discussed and illustrated with real-world systems comprising photovoltaic cells and light emitting devices.[3] Particular emphasis will be put in describing the effect of tailoring the local photonic environment of absorbers and emitters on the device performance, which can be achieved by the integration of different types of optical materials in the device, such as photonic crystals,[4] metallic nanoparticles,[5,6] or dielectric scatterers.[7]

Halide perovskites have become extremely competitive optoelectronic materials because of their high sunlight-harvesting efficiency and notable charge carrier generation/transfer capabilities. These features have been recognized as the key factors for enhancing photoconversion efficiencies in solar photovoltaic devices. Furthermore, their fascinating photoluminescence quantum yield (PLQY) especially in the case of colloidal nanocrystals, induced by a low nonradiative carrier recombination effect, can explain the expansion of their applicability in the wide optoelectronic field. The outstanding PLQY of perovskite nanocrystals is the clear evidence of the significant reduction of non-radiative recombination pathways. Consequently, after photoexcitation, these systems present a pool of photoexcited carriers whose extra energy can be used in an efficient radiative emission or taken advantage of in different ways, such as providing work in solar cells or driving diverse chemical reactions. Here, we shown the application of inorganic halide perovskite nanocrystals in the photocatalytical and photoelectrochemical degradation of Organic compounds, highlighting the potentiality to drive both oxidation and reduction reactions.

Metal halide perovskites in the form of nanocrystals (NCs) are highly efficient light emitters at visible-NIR wavelengths. In this work, the optical properties of single nanocrystals and ensembles will be discussed, as also applications in nanophotonics. At low temperatures, single nanocrystals can be good single photon emitters if blinking and spectral diffusion is conveniently reduced [1]. Moreover, if nanocrystals are forming ordered self-assembed nanocrystals, superfluorescence is observed and characterized by a N-dependent (N = number of nanocrystals in phase giving rise to superfluorescence) intensity and radiative lifetime enhancement [to be published]. Perovskite NCs can be also combined with other semiconductors, as PbS quantum dots and 2D semiconductors, to fabricate more efficient photodetectors [2,3]. In the case of disordered nanocrystal assemblies (films),stimulated emission can be observed with thresholds lower than 10 μJ/cm2 under nanosecond laser excitation at low temperatures, whose physical origin is attributed to single exciton recombination [4]. Eventually, light detecting and emitting devices based on perovskite NCs can be improved by photon recycling effect [5]. Finally, we show the effect of absorption enhancement by using Mie resonators [6] and also the important Purcell enhancement of the spontaneous emission rate in perovskite NCs using HMM structures [7]. A Purcell factor greater than three was demonstrated using CsPbI3 NCs in agreement to the calculated value in the studied HMM structure (Ag/LiF 25/35 nm thick). The thickness of the spacer allows to engineer the exciton-HMM coupling that also induces a noticeable redshift of the emitted PL. However, the HMM structures have the inconvenience of a strong reduction of the NC emission intensity, even if this negative effect can be easily overcome by using Mie scatterers, for example, and further enhancement of the radiative rate of emitters can be obtained [to be published].

Temperature dependent optical linewidths are widely employed in the context of metal halide perovskites and their derivatives to estimate electron-phonon coupling parameters. However, due to comparable contributions from homogeneous and inhomogeneous mechanisms to the spectral broadening, linear spectroscopies like photoluminescence are incapable of isolating the pure dephasing rate and thus are not representative of the system-bath interactions. In these circumstances, nonlinear coherent optical spectroscopy offers insights into the nature of many-body interactions that are entirely inaccessible to temperature-dependent linear spectroscopies. When applied to Ruddlesden-Popper metal halides, these techniques have indeed enabled us to quantify the elastic scattering effects on the exciton dephasing rates. Here, we will discuss the mechanistic nature of exciton-phonon[1], exciton-exciton[2] and phonon-phonon[3] interactions in prototypical Ruddlesden Popper metal halides based on such experimental observations. We will discuss our perspective on how the coherent lineshapes of Ruddlesden-Popper metal halides can be effectively rationalized within an exciton polaron framework. We will also discuss the critical role of the metal cation in the observed coherent exciton dynamics.

The control of the light using the nonlinear optical properties of a given material paves the road towards the full manipulation of an optical wave. A nonlinear material is characterized by the dependence of the refractive index, in both the real and the imaginary parts, by the incoming beam and gives rise to a broad range of applications including switching, optical limiting, supercontinuum generation, or frequency combs, among others. Nevertheless, optical materials are usually characterized by their low nonlinear coefficients, which make difficult or inefficient the development of the aforementioned applications.

            On the other hand, the extraordinary progress of halide perovskite in solar cells or optical sources [1] suggest that this family of materials could present a similar success in the nonlinear generation of the light [2]. For this purpose, it is mandatory to characterize the nonlinear coefficients on these materials. In the present work, a full characterization of β (nonlinear absorption) and n₂ (nonlinear refraction on CH₃NH₃PbX₃ polycrystalline films and colloidal nanoparticles of CsPbX₃ for X = I₃, Br₃ and Br_1.5I_1.5 under pulsed nanosecond excitation is presented [3]. The bright generation of photoluminescence under infrared excitation demonstrates a high two photon absorption coefficient, with values as high as β = 1500 cm/GW. Besides, a modified Z-scan technique with imaging processing is proposed to analyze the nonlinear refraction coefficient (n₂) without the influence of scattering or other undesirable effects. Our experimental data agree quite well with theoretical predictions, demonstrating the accuracy of the method and applications to other materials. Moreover, n₂ parameter reaches values of 3.5 cm²/GW, higher than that found for silicon. Finally, we analyze the potential role of metal halide perovskites as nonlinear photonic materials and propose the potential applications.

I. Suárez: Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites, Eur. Phys. J. Appl. Phys., vol. 75, 30001, 2016.

A. Ferrando, et al.: Toward Metal Halide Perovskite Nonlinear Photonics, J. Phys. Chem Lett., vol.  9, pp.  5612-5623, 2016

I. Suárez, et al.: Outstanding nonlinear optical properties of methylammonium- and Cs-PbX3 (X = Br, I, and Br–I) perovskites: Polycrystalline thin films and nanoparticles, APL Mater., vol.  7, pp.  041106, 2019

Bulk lead halide perovskite thin films have emerged as efficient sensitizers for near-infrared-to-visible upconversion. The upconversion process is based on triplet-triplet annihilation in the annihilator rubrene. Their high absorption cross sections, long free carrier lifetimes and facile bandgap tunability are desirable for photovoltaic applications and are also expected to yield the requisite properties for perovskites to function as efficient triplet sensitizers. It has been well established that lead iodide perovskites of varying compositions are capable of sensitizing the triplet state of rubrene. However, to date, the exact mechanism of the triplet sensitization process is still under debate.

Our currently proposed mechanism is based on a simple charge transfer from the perovskite to the rubrene triplet state. However, the lack of noticeable perovskite photoluminescence quenching in the presence of rubrene supports a more intricate triplet sensitization mechanism. In particular, this highlights that only a small fraction of charges created in the perovskite upon photon absorption is extracted, despite the long-lived nature of free carriers. I will discuss the current view of the triplet sensitization mechanism and address the possible role of localized charge-transfer states, surface and bulk trap states, long-lived defect states or hot carriers.

High environmental stability and surprisingly high efficiency of solar cells based on 2D perovskites have renewed interest in these materials. These natural quantum wells consist of planes of metal-halide octahedra, separated by organic spacers.  Remarkably the organic spacers play crucial role in optoelectronic properties of these compounds. The characteristic for ionic crystal coupling of excitonic species to lattice vibration became particularly important in case of soft perovskite lattice. The nontrivial mutual dependencies between lattice dynamics, organic spacers and electronic excitation manifest in a complex absorption and emission spectrum which detailed origin is subject of ongoing controversy. First, I will discuss electronic properties of 2D perovskites with different thicknesses of the octahedral layers and two types of organic spacer.  I will demonstrate that the energy spacing of excitonic features depends on organic spacer but very weakly depends on octahedral layer thickness. This indicates the vibrionic progression scenario which is confirmed by high magnetic fields studies up to 67T. Furthermore, I will show that in 2D perovskites, the distortion imposed by the organic spacers governs the effective mass of the carriers.  As a result, and unlike in any other semiconductor, the effective mass in 2D perovskites can be easily tailored.  Finally,   I will discuss the exciton fine structure, which result from the exchange interaction between the electron and hole spins leading to a splitting of the bright and dark states.  This splitting can have catastrophic consequences for light emitters which rely on exciton recombination, since the lowest excitonic state is typically dark. I will demonstrate magnetic field induced brightening  of the dark exciton. I will show, that we observe non-Boltzmann distribution of the bright-dark exciton populations, which we attribute to the phonon bottle-neck, which results from the weak exciton-acoustic phonon coupling in soft 2D perovskites. Hot photoluminescence is responsible for the strong emission observed in these materials, despite the significant bright-dark exciton splitting.

In this presentation I will discuss our studies of controlling the charge carrier dynamics, light/matter interactions, and spin populations in these novel hybrid systems. In one effort we are exploring the use of novel organic hybrid systems at and near interfaces to control the carrier dynamics and reduce surface recombination but also to protect grain boundary surfaces from degradation. With respect to controlling spins we have recently studied and developed a novel class of chiral hybrid semiconductors based upon layered metal-halide perovskite 2D Ruddlesden-Popper type structures. These systems exhibit chiral induced spin selectivity whereby only one spin sense can transport across the film and the other spin sense is blocked. From these systems we can achieve a high degree of spin current polarization and injection when used as a contact layer. We have developed novel spin-based LEDs using mixed NCs as the light emitting layer that promotes light emission at a highly spin-polarized interface. The LED spin-polarization is limited by spin-depolarization within the MHP NCs. In a separate effort we have explored the use of chiral copper-halide hybrid systems for circular light polarized detection. Chiral based copper-halide systems combined with highly conductive carbon nanotube networks can be employed to detect circular polarized light with the use of polarizers. Our chiral heterostructure shows high photoresponsivity of 452 A/W, a competitive anisotropy factor of up to 21%, a current response in microamperes, and low working voltage down to 0.01 V. These results demonstrate that the emergent properties of organic−inorganic hybrid systems offer unique opportunities in controlling light, charge and spin..

In another effort we are studying NCs of metal-halide perovskite semiconductors as photocatalysts for light-driven chemical transformations. For photocatalytic applications these NCs are highly photoactive, support charge-separation and migration and have low surface defect densities. We have studied their use as photo-redox systems to drive C-C bond formation reactions. Recently we are taking advantage of the ease of cation substitution at the surface of the NCs to develop a photocatalyst that undergoes multiple sequential inner-sphere photo-oxidation events. A diamine substrate is bound to surface Cu+1 cations, which attract holes from the valence band of the NCs and promotes sequential oxidization of the bound diamine to form a N-N heterocycle.

Solution-processed metal halide perovskites have been recognized as one of the most promising semiconductors, with applications in light-emitting diodes (LEDs), solar cells and lasers. Various additives have been widely used in perovskite precursor solutions, aiming to improve the formed perovskite film quality through passivating defects and controlling the crystallinity. The additive's role of defect passivation has been intensively investigated, while a deep understanding of how additives influence the crystallization process of perovskites is lacking. Here, we reveal a general additive-assisted crystal formation pathway for FAPbI₃ perovskite with vertical orientation, by tracking the chemical interaction in the precursor solution and crystallographic evolution during the film formation process. The resulting understanding motivates us to use a new additive with multi-functional groups, 2-(2-(2-Aminoethoxy)ethoxy)acetic acid, which can facilitate the orientated growth of perovskite and passivate defects, leading to perovskite layer with high crystallinity and low defect density and thereby record-high performance NIR perovskite LEDs (~800 nm emission peak, a peak external quantum efficiency of 22.2% with enhanced stability).

An ongoing demand toward lead-free all-inorganic cesium metal halide perovskites has presented Sn(II) as an ideal substitute of Pb(II) for applications in optoelectronic devices. The major concern regarding Sn(II) is the instability due to the ambient oxidation to Sn(IV). To expand the scope of traditional perovskite and analogues, herein the synthesis and optical performance of Sn(II)-doped CsBr, a new material formed by interstitial doping of Sn(II) into the CsBr matrix, are reported for the first time. This material is prepared following an antisolvent-mediated recrystallization method using a continuous flow reactor, which is beneficial for scaling up the production compared to traditional batch reactors. Sn(II)-doped CsBr exhibits broadband orange emission with full-width-half-maximum of 180 nm and a photoluminescence quantum yield of 21.5 %. The emission turned to be highly stable over 7 months despite containing Sn(II). It is suggested that this is due to the interstitial location of Sn(II) atoms in bulk of microcrystals. A broadband emission and high aerobic stability are attractive properties of the material for white-light emitting applications.

The structural tunability of perovskites has paved the way for applications such as photovoltaics, light-emitting devices, and lasing. Some 2D perovskites are also ferroelectric, making such materials attractive for resistive memory devices. 2D perovskites are of interest for light emission because the emission color of 2D perovskites can be tuned across the visible spectrum. Emission profiles of 2D perovskites typically fall into two categories: “narrow” emission, in which the linewidth of the emitter is < 100 nm, and “broad” emission, for which a single peak can span hundreds of nm. While there is consensus that narrow emission comes from free excitons, the origins of broad emission are under debate. Proposed origins include self-trapped excitons (STEs), phonon replicas, and coupling of STEs to specific point defects. Regardless, many broad-emitting features appear to have strong exciton-phonon coupling. Because perovskite devices typically employ polycrystalline thin films, it is crucial to understand how such light-matter interactions are affected by thin film growth.

Here, we investigate thin film growth of the broad-emitting and ferroelectric perovskite (EA)₄Pb₃Br₁₀. [1] This phase exhibits three emission features; we find that two of them are phonon-coupled. Notably, film strain turns off the broad, phonon-coupled emission. This broad emission can be recovered by slowing the growth kinetics of the thin film and eliminating strains. Photothermal deflection spectroscopy shows that strain increases electronic disorder near the free exciton absorbance onset. In addition, the challenge of making phase-pure films in low-dimensional Ruddlesden-Popper structure ((A’)2(A)n−1BnX3n+1) is overcome by using a single A/A’-site cation, ethylammonium (EA), whose optimal size also prohibits formation of off-target phases. These results reveal 1) a way to tune phonon-coupled emission in films that is not available to bulk crystals, 2) that care should be taken to account for the effects of strain when studying exciton-phonon coupling in thin films and 3) that such film strain should be accounted for when making resistive memory devices, as ferroelectric domains can be affected by strain.

[1] Kennard, R.M., Dahlman, C.J., Chung, J., Cotts, B.L., Mikhailovsky, A.A, Mao, L., DeCrescent, R.A., Stone, K.H., Venkatesan, N.R., Mohtashami, Y., Assadi, S., Salleo, A., Schuller, J.A., Seshadri, R. and Chabinyc, M.L. Growth-Controlled Broad Emission in Phase-Pure Two-Dimensional Hybrid Perovskite Films. Accepted to Chemistry of Materials, 2021.

Wide bandgap mixed-halide perovskites as the top absorbers in tandem solar cells typically exhibit a larger voltage deficit in contrast to their corresponding tri-iodide-based perovskites. With this work we are tackling the challenge of directly correlating the multi-stage synthesis of bromide-containing perovskites with optoelectronic properties and consequently device performance. Our results show that the incorporation of bromide occurs via a halide homogenization process where the perovskite composition transitions from an initial bromide-rich phase to the final target stoichiometry. In situ photoluminescence measurements during synthesis reveal that bromide inclusion alters the formation dynamics. By combining experiments with first-principle calculations we suggest that the formation of FAMACsPb(I_0.8Br_0.2)₃ starts with the nucleation of a bromide-rich phase from solution during supersaturation followed by a retarded growth stage. The retarded growth stage is associated with a halide homogenization process that brings the composition of crystallized material to the target stoichiometry. This homogenization process not only changes the formation dynamics of mixed-halide perovskites but also promotes defect formation, which consequently leads to increased non-radiative recombination losses in the final perovskite film and thus, could contribute to the larger voltage deficit.

Metal halide perovskites are mixed electronic-ionic semiconductors with an extraordinary rich optoelectronic behavior and the capability to function very efficiently as active layers in solar cells, with a record efficiency surpassing 24 percent nowadays.

In this talk you are watching,  I review recent work of our group in which we apply experimental protocols and drift-diffusion modeling to provide a consistent interpretation of the signals observed in the impedance spectrum. Based on that, I will present procedures to extract relevant information from the spectra, such us charge collection efficiencies, ideality factors and recombination mechanisms, ionic diffusion coefficient and ion vacancy concentrations.

Among several intriguing properties of soft lead halide perovskite crystals, viscoelasticity describes well the mechanical response of the material. In this work we show a close connection between viscoelasticity and trap dynamics in lead halide perovskites. We studied PL fluctuation kinetics of MAPbI3 sub-micrometer crystals employing statistically correct power spectral density (PSD) estimation method which reveals 0.5-10 s as the working timescale of the intrinsic PL quenchers. This is also the maximal timescale of the reversible trap activation and deactivation in these crystals. Among many popular semiconductor materials (e.g., conjugated polymers, traditional quantum dots) only halide perovskites are found to possess such characteristic timescale which matches very well with its viscoelastic response time. Super-resolution Localization analysis demonstrates that this timescale is intrinsic to the material and polycrystalline nature of the microcrystals has negligible effect on it. Moreover, we reveal presence of photoinduced nonradiative recombination channels which work in faster timescale (>0.3 s).

In a film, grains and crystallites are spatially close or interconnected through grain boundaries. Consequently, carrier recombination and trap dynamics are found to be even more complex than that of an isolated crystal. We developed an advanced mapping method based on correlation of the PL signal to identify different regions in a film having variation in recombination behavior. Direct comparison of the PL fluctuation of each cluster in the map with electron microscopy image provides important insight about microscopic domains of the nonradiative traps. PSD of the PL fluctuation reveals that a large fraction of spatially isolated clusters has common timescale of fluctuation (0.3 s) which is again closely matching with the viscoelastic response time of the material.

In this study, hyperbolic metamaterials (HMM) are properly designed, simulated and fabricated as an outstanding photonic structure able to control the emission rate of lead halide perovskite nanocrystals (PNCs) deposited on the top. Geometrical parameters (thicknesses of the metal and the dielectrics layer) are optimized to enhance coupling between the HMM and the exciton confined in the PNCs. The device is tested for CsPbI₃ PNCs which demonstrate an increase of the exciton radiative recombination rate by more than a factor of 3 together with the 8nm red shift of the emission spectra when the PMMA spacer is 10 nm. The appearance of this redshift exhibits a strong correlation with the coupling of perovskite emitters to the HMM modes. However, the emitter-HMM coupling also produces a decrease of the PL intensity, due to the preferential emission of light into the high-k HMM modes. This negative effect can be overcome by modifying the HMM with diffraction effects or light scattering centers. The second strategy can be easily implemented by simultaneously dispersing onto the HMM/PMMA substrate TiO₂ nanospheres together with the perovskite NCs. We saw two distinct beneficial outcomes as a result of this: (i) a significant rise in PL intensity, and (ii) further Purcell enhancement. After deconvolution of the system response, we find that the exciton lifetime is reduced from 0.75 ns (only perovskite NCs) to 0.45 ns (perovskite NCs and TiO₂ nanospheres on top of the HMM structure). This results in a Purcell factor increase from 2 (considering here we used a 20 nm PMMA spacer) to greater than 3.3, which is significantly higher than the NC-HMM system's calculated value. This additional Purcell enhancement can be attributed to the Mie resonant effect of the TiO₂ nanospheres near the HMM surface. Furthermore, the significant rise in PL intensity in these samples containing TiO₂ nanospheres may be attributed to emitter radiative rate enhancement and changes in emission directionality.

Self-assembled monolayers as hole-transporting materials for increasing the performance of Perovskite CsPbBr₃ Quantum Dot Light Emitting Diodes

S. Kumari* , E. Martinez-Ferrero and E. Palomares

Institut Catala d'investigacio Química (ICIQ), Tarragona-43007 Spain

^* skumari@iciq.es

Abstract: PEDOT:PSS is one of the most commonly used hole transport material in optoelectronic devices due to its noble behavior like quality film making capability, thermal stability and high conductivity. However, due to its hygroscopic and acidic nature, PEDOT: PSS strongly compromises the stability of the devices. In the same field, other commonly used alternative for HTM is PTAA which being very expensive makes its application less benefitting. Therefore, we need to find an alternative for these popular and solution-processed materials. Self-assembled monolayers (SAMs) formed by organic molecules are an interesting alternative for common hole transport materials (HTMs). The assembly of the molecules results in films of less than 5 nm that are enough to modify the physicochemical properties of the anode, like the wettability and the work function. SAMs have a definite dipole moment which can shift the work function of anode by forming covalent bonds at the interface. Its low cost, less material usage, and the ease of tuning the molecular structure make SAMs attractive for HTM when compared with PEDOT: PSS/PTAA assembly.

In the present work, we report our results of quantum dot light emitting diodes (QDLEDs) prepared with two carbazole-based molecules, EADR03 and EADR04, as self-assembled monolayers as HTM in the Perovskite CsPbBr₃ -based QDLEDs. We have studied the device performance of the QDLEDs with SAM molecules and compared with the reference devices containing PEDOT:PSS/PTAA and PTAA. The luminance from the devices with EADR04 and EADR03 HTL has increased, when compared with PEDOT:PSS/PTAA and PTAA  devices. Interestingly, lifetime of the devices at constant applied bias has also increased.

The new thin HTLs based on SAM molecules can open a new pathway for LEDs industries, due to its ease of processing and thin-size devices possibilities.

Keywords: SAMs, Perovskite, Quantum dots, Light emission, Materials

References:

E. Aktas, E Phung et al, Energy Environ. Sci., 2021,14, 3976-3985

E. Yalçin et al, Energy Environ. Sci., 2019, 12, 230-237

Leimeng Xu et al, Nature Communications , 2020, 11, 1-12

Cesium Lead Iodide perovskite (CsPbI₃) is the most suitable fully inorganic perovskite for optoelectronic applications due to its proper band gap around 1.77 eV. However, it only concerns for the “black” optically active phase (α) which is only stable at temperatures above 310ºC with a subsequent degradation to the β and γ active phases and eventually to the “yellow” non-optically active orthorhombic phase (δ) which is the most stable phase at room temperature.

Here, we propose a scaffold assisted synthesis of CsPbI3 nanocrystals with “black” optically active phase. The synthesis does not require ligands nor additives. Simply using a porous network that consists in a stack of SiO2 nanospheres, we create a mesoporous scaffold with a 50% porosity which allows a further infiltration of a CsPbI3 precursor solution. After a mild thermal treatment, we obtain nanocrystals thanks to the strain conferred by the matrix during crystal growth. Nanocrystals optical properties can be tuned by means of quantum confinement effects either as a consequence of a variation in the precursor concentration solution but also by means of Iodine/Lead ratio alteration. Furthermore, the careful filling of the matrix enables an efficient charge transport between q-dots by percolation mechanism. This allow us to fabricate solar cells or deep-red emission devices

Transient photoluminescence (trPL) characterization experiments allow to analyze charge carrier dynamics and identify the recombination channels of the device structure under investigation. Useful information that can be extracted includes the quantification of radiative and non-radiative lifetimes,^[1] charge carrier extraction from differential lifetime computation^[2], and the influence of the interfaces on the recombination mechanism.^[3]
Fitting the experimental results with simulations further supports the analysis of the obtained data. However, qualitatively comparable fittings can be obtained with different sets of simulation parameters. In fact, in the trPL decay, the radiative and non-radiative recombination processes follow a quadratic and linear dependence on the photogenerated carriers, respectively. The carriers also depend on the incident light intensity and the doping of the emitting material. This interdependence can lead to erroneous conclusions and a robust approach to obtain simulations that are independent of the user proficiency is necessary. 
Using the fully-coupled, 1-dimensional optoelectronic simulation software setfos, the trPL signal of a simple glass/perovskite structure was simulated and a routine is suggested to ascertain the reliability of the results. This routine is based on experimentally measured material properties and the analysis of the band diagram evolution during the photoluminescence transient. The validity of the simulated trPL is also recursively verified by fitting the decay with a bi-exponential function to extract the lifetimes of the recombination mechanisms.
This approach is not limited to bare perovskite and eventually, a first analysis of the influence of layer interfaces on trPL will be presented.
The mentioned routine for trPL simulation can be further extended with the inclusion of the photon recycling phenomenon.^[4]

[1] Kirchartz, T.; Márquez, J. A.; Stolterfoht, M.; Unold, T. Photoluminescence‐Based Characterization of Halide Perovskites for Photovoltaics. Adv. Energy Mater. 2020, 10, 1904134.

[2] Staub, F.; Hempel, H.; Hebig, J.-C.; Mock, J.; Paetzold, U. W.; Rau, U.; Unold, T; Kirchartz, T. Beyond Bulk Lifetimes: Insights into Lead Halide Perovskite Films from Time-Resolved Photoluminescence. Phys. Rev. Appl. 2016, 6, 044017.

[3] Haddad, J.; Krogmeier, B.; Klingebiel, B.; Krückemeier, L.; Melhem, S.; Liu, Z.; Hüpkes, J.; Mathur, S.; Kirchartz, T. Analyzing Interface Recombination in Lead‐Halide Perovskite Solar Cells with Organic and Inorganic Hole‐Transport Layers. Adv. Mater. Interfaces 2020, 7, 2000366.

[4] Aeberhard, U.; Zeder, S.; Ruhstaller, B. Reconciliation of dipole emission with detailed balance rates for the simulation of luminescence and photon recycling in perovskite solar cells Opt. Express 2021, 29, 14773.

Perovskite photovoltaics are slated to revolutionize terrestrial power generation by providing a low cost, higher performance alternative to existing technology. Perovskite solar cells also offer distinct advantages for generation of electricity in space due in addition to the properties listed above but also light weight packing, radiation tolerance, better performance under LILT conditions, and more. NREL and NASA recently launched a batch of perovskite solar cells to experience the space environment for a year on the side of the international space station as part of MISSE-15. In this talk I will discuss the design criteria to develop perovskites specifically for space operation. Additional considerations include the device architecture (whether tandem or single junction), packaging, thermal coefficients, radiation testing for various environments, and operation under the solar spectrum AM0. I will discuss in detail radiation interactions with Perovskite absorbers and compare this to traditional semiconductors.

Halide perovskites are poised to realize the next generation of inexpensive yet high-performance optoelectronic devices, yet our understanding of key photophysical processes is still emerging. Here, I will cover our group's latest work on understanding photons in and photons out of these fascinating semiconductors, as well as the recombination processes occurring in between. I will cover our efforts on neat films as well as integrated perovskite/silicon tandem cells, perovskite/perovskite tandem cells and LEDs, covering both modelling and experimental imaging. I will cover important effects including light coupling between multi-layered stacks and non-radiative recombination processes. These efforts are pushing forward our understanding and leading to new strategies to optimise performance. 

Perovskite LEDs are an exploding field, with high performance red and green devices demonstrated by many groups. Blue LEDs, however, have lagged significantly behind these two colors in both efficiency and stability. Here, we identify material and device improvements that allow these blue materials to be more competitive with their red and green cousins. We demonstrate that the addition of a small amount of a Mn dopant improves the photoluminescence efficiency by a factor of 3, an improvement that translates directly to blue and white devices, leading to efficiency and stability enhancements. Finally, we will detail recent measurements into the source of this improvement.