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Cost-effective production of perovskite solar cells on an industrial scale requires the utilization of exclusively inexpensive materials. However, to date, highly efficient and stable perovskite solar cells rely on expensive gold electrodes since other metal electrodes are known to cause degradation of the devices. Finding a low-cost electrode that can replace gold and ensure both efficiency and long-term stability is essential for the success of the perovskite-based solar cell technology. In this work, we systematically compare three types of electrode materials: multi-walled carbon nanotubes (MWCNTs), alternative metals (silver, aluminum, and copper), and transparent oxides [indium tin oxide (ITO)] in terms of efficiency, stability, and cost. We show that multi-walled carbon nanotubes are the only electrode that is both more cost-effective and stable than gold. Devices with multi-walled carbon nanotube electrodes present remarkable shelf-life stability, with no decrease in the efficiency even after 180 h of storage in 77% relative humidity (RH). Furthermore, we demonstrate the potential of devices with multi-walled carbon nanotube electrodes to achieve high efficiencies. These developments are an important step forward to mass produce perovskite photovoltaics in a commercially viable way. Published by AIP Publishing. The authors would also like to gratefully acknowledge Solliance for the financial support, the Initiating and Networking funding of the Helmholtz Association (HYIG of U. Paetzold), and the European Research Council (FP7 ERC StG HIENA - 337739 of M. de Volder). This research has received (partial) funding from the Flemish Government-Department of Economics, Science and Innovation.

We show an active artificial iris based on solely thin-film components, wherein several LCD elements are controlled a metal-oxide TFT and by powered by thin-film photovoltaics (TFPV). Key aspects for the driver are size and low power consumption. We demonstrate power consumption down to 25μW for the full iris.

This work describes a patterning technique for the photoactive layer of organic photovoltaic modules. We demonstrate the fabrication of efficient poly[3-(hexyl)thiophene-2,5-diyl]:[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) based organic photovoltaic modules through a specific surface treatment, based on the deposition of a fluorinated self assembled monolayer (SAM) on top of the bottom electric contact. Direct self-patterning of the photoactive layer is achieved by the high contact angle between the SAM and the polymer solution, while a smooth topography is created by combining two solvents with different surface tensions and boiling points in the polymer:PCBM solution. The resolution of the patterning is approximately 400 μm for modules based on a conventional cell architecture and 120 μm for an inverted architecture. As a result, we show 25 cm2 P3HT:PCBM based organic photovoltaic modules with 10 series-connected cells, fabricated via roll-to-roll compatible deposition and patterning techniques.

We report on the development and implementation of nanophotonic front electrodes for perovskite thin-film solar cells. An improvement in power conversion efficiency is demonstrated and explained based on three-dimensional electromagnetic simulations.

© The Royal Society of Chemistry 2016. Transitioning perovskite photovoltaics from the rapid progress in lab-scale devices to industrially viable large area modules is a key challenge for the economic breakthrough of the technology. In this work, we demonstrate ultrasonic spray coating as a scalable and versatile linear deposition technique for high efficiency perovskite photovoltaics. We show the versatility of concurrently pumped ultrasonic spray coating by rapidly and precisely optimizing precursor ratios based on PbCl2, Pb(CH3CO2)2·3H2O, PbBr2, CH3NH3Br, and CH3NH3I to achieve highly crystalline and pinhole-free layers. Initial power conversion efficiencies of 15.7% for small scale devices and 11.7% for 3.8 cm2modules were achieved with current-voltage sweeps and tracked to 13.4% for devices and 10.4% for modules under continuous illumination and bias at the maximum power point. Process versatility is further demonstrated with the in situ bandgap control in CH3NH3PbIxBr3-xlayers. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal history: Received 25 January 2016; Accepted 4 February 2016; Accepted Manuscript published 4 February 2016; Advance Article published 15 February 2016; Version of Record published 1 March 2016 ispartof: Journal of Materials Chemistry A vol:4 issue:10 pages:3792-3797 status: published

Replacing toxic solvents with nonhazardous solvents is one of the key challenges for industrial scale commercialization of thin film perovskite photovoltaics. Here, nonhazardous solvent/alcohol/acid systems are presented for the single-step deposition of pinhole-free perovskite layers with combined lead halide precursors of Pb(CH3CO2)(2), 3H(2)O, PbCl2, and CH3NH3I. Comparable performance to standard hazardous inks is achieved: devices with 15.1% power conversion efficiency are demonstrated and maintain 13.5% tracked for 5 min at maximum power point. Blade coated 4 cm 2 solar modules fabricated with highest performing device ink attain 11.9% in power conversion efficiency. K.L.G. and J.G.T. contributed equally to this work. The work of K.L.G. was supported by the Roger Van Overstraeten Society. The work of J.G.T. was partially supported by the Natural Science and Engineering Research Council of Canada. The work of U.W.P. was supported by the German Academic Exchange Service. This work has been partially supported by Solliance, a partnership of R&D organizations from Belgium, the Netherlands, and Germany working in thin film photovoltaic solar energy.

We perform optical loss analyses and energy yield modelling of perovskite/silicon multijunction solar cells to elucidate the superiority of different architectures, e.g., 4-terminal solar cells and 2-terminal solar cell.

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Stability is one of the key challenges for industrial scale commercialization of perovskite solar cells. In this work, a degradation mechanism that depends on materials and bias conditions of the device during light-soaking is proposed. The observed degradation is linked to the additive 4-tert-butyl pyridine (tBP), crucial to the hole transport layer of most perovskite solar cells, and gold. This conclusion is reached through the statistical analysis of multiple compositional profiles of light-soaked and nonlight-soaked devices and by selective replacement of material layers of the device. Moreover, the rate of the light-induced degradation is enhanced by operation at forward bias, which is required for power generation. Thus, this work stresses the need for the development of transport layers that do not require tBP, and to replace gold to produce high-performing devices that are also stable under operating conditions. ispartof: ADVANCED ENERGY MATERIALS vol:8 issue:23 status: published

We show the impact of lateral structuring on the optical properties of organic thin films in microcavities. The active material tris-(8-hydroxy quinoline) aluminium (Alq3) was deposited using shadow mask evaporation, resulting in various micron sized shapes. A simplified box model is employed to describe the steady state electric field distribution in these mesa cavities. The complex mode structure measured in transmission and photoluminescence is confirmed by a transfer matrix calculation and a Fourier transform of the internal electric field distribution.

We report on the dynamics of laser emission from an anisotropic organic microcavity filled with the guest-host composite of tris-(8-hydroxy quinoline) aluminium (Alq3) and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). In a single microcavity, a linesplitting of 0.18 THz between two perpendicularly polarized laser modes is observed. We ascribe this effect to an optical anisotropy in the distributed Bragg reflectors surrounding the organic layer. The temporal behavior of the electromagnetic field is studied by an up-conversion technique and shows an optical beating of 0.18 THz. Two modeling approaches are used to gain insight in the temporal evolution and phase behavior of the two modes. Both point towards the presence of a phase-coupling mechanism in this system.

The need for scalable and environmentally friendly deposition of organic semiconductors is mounting, as lab-scale solution processed organic photovoltaic (OPV) devices have been certified with 10.8% efficiency. The replacement of toxic halogenated solvents is a priority in the commercialization of solution processed OPV. Here we introduce several solvent systems based on thiophene, tetraline, 1,2,4-trimethylbenzene, xylene, and anisole for the blade coating of diketopyrrolopyrrole-based polymer: fullerene OPV devices. These devices attain 6.1% efficiency, greater than the commonly used chloroform:ortho-dichlorobenzene solvent systems for the same polymers, and without involving the post-deposition annealing treatments nor additives typically implemented for non-halogenated inks. Furthermore, the solubility of the material was investigated with Hansen Solubility Parameters, and coatability on a variety of substrates was probed via contact angle measurements. This work enables a new non-halogenated solvent route for the scalable fabrication of organic electronics.

© 2015 AIP Publishing LLC. The charge carrier transport in thin film hybrid solar cells is analyzed and correlated with device performance and the mechanisms responsible for recombination loss. The hybrid bulk heterojunction consisted of a blend of poly(3-hexylthiophene) (P3HT) and small size (2.4 nm) PbS quantum dots (QDs). The charge transport in the P3HT:PbS blends was determined by measuring the space-charge limited current in hole-only and electron-only devices. When the loading of PbS QDs exceeds the percolation threshold, a significant increase of the electron mobility is observed in the blend with PbS QDs. The hole mobility, on the other hand, only slightly decreased upon increasing the loading of PbS QDs. We also showed that the photocurrent is limited by the low shunt resistance rather than by space-charge effects. The significant reduction of the fill factor at high light intensity suggests that under these conditions the non-geminate recombination dominates. However, at open-circuit conditions, the trap-assisted recombination dominates over non-geminate recombination. ispartof: Journal of Applied Physics vol:117 issue:095503 pages:3-10 status: published

The optical properties of microcavities (MCs) are strongly dependent on both polarization of incident and emitted light and its angle of observation. Here we report the measurements of cw- and time-resolved photoluminescence (PL) observed at negative detuning and at resonance for s- and p-polarization in the strong coupling regime of a planar MC containing J-aggregates of a cyanine dye. Following non-resonant excitation, the emission spectra consist of three types of features: direct J-aggregate exciton emission, polariton emission, and uncoupled monomer emission through the transmission maxima of the distributed Bragg reflector beyond the stop-band. We compare our experimental results with a transfer-matrix calculation of the transmission for s- and p-polarization and explain the different positions of the polariton branches, the stop-band width, and the high- and low energy transmission maxima of the MC. Time-resolved PL experiments show an increase in the decay lifetime of the exciton-like mode when it is positioned far from the cavity mode. Close to resonance, the lower polariton branch decays with the natural lifetime of the J-aggregates.

The fabrication of high-quality cesium (Cs)/formamidinium (FA) double-cation perovskite films through a two-step interdiffusion method is reported. CsxFA1-xPbI3-y(1-x)Bry(1-x) films with different compositions are achieved by controlling the amount of CsI and formamidinium bromide (FABr) in the respective precursor solutions. The effects of incorporating Cs+ and Br− on the properties of the resulting perovskite films and on the performance of the corresponding perovskite solar cells are systematically studied. Small area perovskite solar cells with a power conversion efficiency (PCE) of 19.3% and a perovskite module (4 cm2) with an aperture PCE of 16.4%, using the Cs/FA double cation perovskite made with 10 mol% CsI and 15 mol% FABr (Cs0.1FA0.9PbI2.865Br0.135) are achieved. The Cs/FA double cation perovskites show negligible degradation after annealing at 85 °C for 336 h, outperforming the perovskite materials containing methylammonium (MA).

Multijunction solar cells employing perovskite and crystalline-silicon (c-Si) light absorbers bear the exciting potential to surpass the efficiency limit of market-leading single-junction c-Si solar cells. However, scaling up this technology and maintaining high efficiency over large areas are challenging as evidenced by the small-area perovskite/c-Si multijunction solar cells reported so far. In this work, a scalable four-terminal multijunction solar module design employing a 4 cm2 semitransparent methylammonium lead triiodide perovskite solar module stacked on top of an interdigitated back contact c-Si solar cell of identical area is demonstrated. With a combination of optimized transparent electrodes and efficient module design, the perovskite/c-Si multijunction solar modules exhibit power conversion efficiencies of 22.6% on 0.13 cm2 and 20.2% on 4 cm2 aperture area. Furthermore, a detailed optoelectronic loss analysis along with strategies to enhance the performance is discussed.

The authors present experimental results on mechanically stacked organic solar modules and their advantage over standard tandem architectures. A four-terminal configuration of two single junction modules with complementary absorbing active layers uses the more efficient energy conversion of a tandem structure without the necessity of matching currents or voltages of electrically connected subcells. The presented combination of semitransparent and opaque solar cells consists of solution processed polymer-fullerene blends as active materials. A cost-effective mechanical scribing process is applied for the patterning of the deposited layers. The best devices have an efficiency of over 6.5% on an aperture area of 16 cm2 which equals a gain of 30% over the best single junction module fabricated by the same process. Optical simulations demonstrate a 32% increased annual energy output of a mechanically stacked device in comparison to a monolithic tandem structure using an equivalent geometry. © 2013 SPIE.

A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure.

We report on three-dimensional numerical optical simulations of the emission extraction efficiency in light emitting devices with field effect carrier transport. The finite difference time domain (FDTD) method is applied for organic thin film structures on silicon substrates with metal and metal oxide electrodes. Simulations are performed for Au, Ag and indium tin oxide electrodes in bottom gate, bottom contact geometries. Special attention is paid on the dependence on electrode thickness and contact shape. It is demonstrated that in unipolar driven devices with Si gate, silicon dioxide insulator and 40 nm-thick organic films the maximum out-coupling efficiency is below 10 %. This value can be doubled by an implementation of metal reflecting layers on the Si substrate. Furthermore, the emission efficiency in the ambipolar regime is investigated. The results present the dependence of light extraction on the distance between light source and electrode. Additionally, the influence of the contact edge shape is investigated for two different designs with rectangular and wedge electrodes. Interference effects cause an oscillation in the distance dependence.

We investigate the optical properties of laterally confined organic microcavities. For preparation, a shadow mask deposition technique is used, which results in laterally shaped organic dots with micrometer size as the cavity layer. To describe the steady state electric field distribution in these structures, a simplified box model is applied. The complex mode structure measured in transmission and photoluminescence is simulated by transfer matrix calculations and a Fourier transform of the internal electric field distribution.

We present a study of time-resolved transmission and emission properties of optically anisotropic planar micro-cavity structures. The structures consist of /4-layers of SiO 2 and TiO 2 for the dielectric mirrors and a cavitylayer of either SiO 2 or the organic dye composite AlQ 3 /DCM. For the SiO 2 cavity, we observe a polarizationsplitting at normal incidence leading to terahertz oscillations of transmitted coherent light. The polarizationsplitting is explained by an optical anisotropy of the dielectric layers caused by the fabrication process. Weapply an up-conversion setup for temporally and spectrally resolved transmission measurements and obtain acorresponding beating of 1.25 THz. Time resolved measurements yield a Q-value of 1600, corresponding to acavity photon lifetime of 0.65 ps. We explain our observations with a transfer-matrix model and introduce aFourier-transform based analytical algorithm. The cavity “lled with the organic dye composite can act as anorganic microcavity laser. The birefringence of the distributed Bragg re”ectors leads to lasing in two perpen-dicularly polarized modes. Investigations of the ultrafast dynamics of this laser system show a phase couplingof the two laser modes leading to the generation of a terahertz optical beat. The oscillation frequency can bewidely tuned by variations in the fabrication process.Keywords: Terahertz oscillation, Polarization splitting, Microcavity, Dielectric layer anisotropy, Organic laser

We report on the experimental observation of polarization splitting and terahertz oscillations in transmission and laser emission from optically anisotropic microcavities. A guest-host composite of tris-(8-hydroxyquinoline) aluminium (Alq3) and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) serves as active laser material. The anisotropy is attributed to oblique columnar structures in the distributed Bragg reflector mirrors of our microcavity, resulting from sample fabrication. A splitting of 0.2 nm occurs in the laser emission from an organic vertical cavity surface emitting laser at a wavelength of 612.6 nm, and a splitting of 2.5nm is obtained from a sample for Ti-Sapphire laser transmission at 781 nm. Split modes are perpendicularly polarized. An upconversion setup allows temporally resolved studies of transmission and emission behavior, showing an oscillation at a frequency of 1.25THz in transmission, and 0.18THz in emission, respectively. The temporal behavior of laser emission is modelled by a set of rate-equations and extended to account for the resulting oscillations. Our observations suggest that a phase-coupling mechanism between both occuring modes is present in the laser emission from our microcavity.

Organic light-emitting diodes (OLEDs) usually exhibit a low light-outcoupling efficiency of only 20%. Typically, more than 30% of the available power is lost to surface plasmons (SPs). Consequently, the overall efficiency could be strongly enhanced by recovering SP losses. Therefore, three suitable techniques for extracting SPs-index coupling, prism coupling, and grating coupling-are discussed from a theoretical point of view and investigated experimentally in simplified OLED-like structures. The basic physical processes are clarified by systematic variations of the involved layer thicknesses and by excited state lifetime measurements. In addition, the analysis of the results is supported by optical simulations based on a dipole model. Finally, the advantages and disadvantages of each method, their potential efficiency for recovering SP losses, as well as the applicability in OLEDs are compared.

Organic light-emitting diodes (OLEDs) usually exhibit a low light outcoupling efficiency because a large fraction of power is lost to surface plasmons (SPs) and waveguide modes. In this paper it is demonstrated that periodic grating structures with almost µm-scale can be used to extract SPs as well as waveguide modes and therefore enhance the outcoupling efficiency in light-emitting thin film structures. The gratings are fabricated by nanoimprint lithography using a commercially available diffraction grating as a mold which is pressed into a polymer resist. The outcoupling of SPs and waveguide modes is detected in fluorescent organic films adjacent to a thin metal layer in angular dependent photoluminescence measurements. Scattering up to 5th-order is observed and the extracted modes are identified by comparison to the SP and waveguide dispersion obtained from optical simulations. In order to demonstrate the low-cost, high quality and large area applicability of grating structures in optoelectronic devices, we also present SP extraction using a grating structure fabricated by a common DVD stamp.

The authors report on color controllable white light emission from a unipolar organic light emitting transistor. We demonstrate light emission with two distinct peaks: a spectrally narrow blue emission from monomers and a yellow broadband emission created close to the interface of the organic film and SiO2. Due to the functionality of Mg/Au stacked electrodes, we are able to position the recombination zone via gate voltage control. Therefore, we are able to shift the spectral peak position and change the emission intensity independently by the drain voltage. The emission color is tunable from CIE coordinates (0.27, 0.28) to (0.40, 0.41).

The authors report on blue light emitting unipolar organic light emitting transistors (OLETs) with external quantum efficiency up to 0.2% by using multifunctional Mg/Au electrodes formed in combination with an efficient light emitting fluorene derivative. A mobility up to 6×10−6 cm2 V−1 s−1 has been achieved, which is comparable to previous results from time of flight mobility measurements. An anomalous light emission behavior is observed in unipolar OLETs. The phenomenon is discussed in light of the effects of electron injection and outcoupling efficiency, respectively. Our results show that the multifunctional electrodes are useful for implementing highly efficient unipolar OLETs.

The authors report on three-dimensional numerical optical simulations of the emission outcoupling efficiency in light-emitting devices with a field-effect carrier transport. The finite difference time domain method is applied to organic thin film structures on a silicon substrate with metal and metal oxide electrodes. Simulations are performed for Au, Ag, and indium tin oxide electrodes in a bottom gate, bottom contact geometry. Additional attention is paid to the dependence on electrode thickness and contact shape. We demonstrate that in unipolar driven devices with Si gate, silicon dioxide insulator, and 40 nm thick organic films, the maximum outcoupling efficiency is below 10%. This value can be increased by the implementation of a metal reflecting layer on the Si substrate. In further studies, the emission efficiency in the ambipolar regime is investigated. The result presents the dependence of light extraction on the light source-electrode distance for rectangular and wedge shaped contacts.

We report on the optical mode structure of laterally confined organic microcavities. For preparation, an organic semiconductor is evaporated through a mask with square sized holes, resulting in photonic dots with approximately 5μm diameter. Using a microscope setup, we observe a complex mode structure in transmission and photoluminescence. From the mode mapping, we conclude a strong three-dimensional optical confinement. The near and far field spectra are modeled by transfer matrix calculations and a Fourier transform of the internal electric field distribution, respectively.

The authors present time-resolved studies of laser emission from an organic microcavity filled with a guest-host composite of tris(8-hydroxy quinoline) aluminium and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran. A line splitting of 0.18THz between two perpendicularly polarized lines is observed, resulting from an optical anisotropy in the distributed Bragg reflectors. This particular behavior is attributed to oblique columnar structures shaped by off-axial preparatory conditions. By means of an upconversion setup an oscillation at 5.5ps period time and phase coupling of the modes are observed. A rate-equation-based approach is utilized for modeling the temporal behavior.

We report the experimental observation of polarization splitting at normal incidence and terahertz oscillations of transmitted light from a single planar microcavity. Optical anisotropy in the SiO2∕TiO2-dielectric mirrors leads to two perpendicularly polarized transmission modes. We ascribe the anisotropy to oblique columnar structures in the dielectrics resulting from off-axial growth of the microcavity structure. We apply an up-conversion setup for temporally and spectrally resolved measurements and obtain a corresponding beating of 1.25THz. Time resolved measurements yield a cavity photon lifetime of 0.65ps, corresponding to a Q value of 1600. To explain our observations we introduce a Fourier-transform based analytical model.

We investigate the dynamics of the organic laser guest-host composite of tris-(8-hydroxy quinoline) aluminium and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran embedded in a high-Q (Q≈4500) double distributed Bragg reflector microcavity using subpicosecond up-conversion techniques. Lasing is observed at a threshold of 0.4nJ∕20μJcm−2 with a linewidth of 0.05 nm (resolution limit). We observe a strongly nonlinear intensity-dependent delay of the emitted radiation burst. All experimental results are successfully modeled by a set of nonlinear rate equations, emphasizing the importance of a feedback mechanism for lasing.

Organometallic halide perovskites are non-epitaxial low-temperature semiconductors that show great promise in light-emission applications due to their favorable optoelectronic properties. Though high external quantum efficiencies exceeding 20% have been shown for perovskite LEDs, this is usually achieved at low current densities, and hence corresponds to low brightness. To reach high brightness, it is important to make strides in stability and quantum efficiency at high current density. In this work, we scale the active area of methylammonium lead iodide perovskite LEDs from 1000 μm in diameter down to tens of microns dimensions, relevant for emissive displays and laser devices that require high brightness. We systematically examine active-area-dependent perovskite LED performance from mA cm−2 up to kA cm−2 current density regimes by means of quasi-DC, DC, and sub-μs pulsed driving. For perovskite LEDs with diameters of 50 μm on glass substrates, we achieve T50 stability above 10 h under continuous operation at 500 mA cm−2 and above 5 h at 1000 mA cm−2, respectively. By using short electrical pulses, we significantly reduce the amount of dissipated thermal energy and show that this leads to reliable electrical operation up to 5 kA cm−2 for such small perovskite LEDs fabricated on sapphire substrates.

The perovskite solar cell is considered a promising candidate as the top cell for high-efficiency tandem devices with crystalline silicon (c-Si) bottom cells, contributing to the cost reduction of photovoltaic energy. In this contribution, a simulation method, involving optical and electrical modelling, is established to calculate the performance of 4-terminal (4T) perovskite/c-Si tandem devices on a mini-module level. Optical and electrical characterization of perovskite and c-Si solar cells are carried out to verify the simulation parameters. With our method, the influence of transparent conductive oxide (TCO) layer thickness of perovskite top cells on the performance of tandem mini-modules is investigated in case of both tin-doped indium oxide (ITO) and hydrogen-doped indium oxide (IO:H). The investigation shows that optimization of TCO layer thickness and replacement of conventional ITO with highly transparent IO:H can lead to an absolute efficiency increase of about 1%. Finally, a practical assessment of the efficiency potential for the 4T perovskite/c-Si tandem mini-module is carried out, indicating that with a relatively simple 4T tandem module structure the efficiency of a single-junction c-Si mini-module (19.3%) can be improved by absolute 4.5%.

We present variable-size circular micro methylammonium lead iodide PeLEDs and systematically examine their performance in moderate and high current density regimes. We demonstrate the beneficial influence of device downscaling on the internal heat generation and its positive impact on lifetime. For micron size glass-based devices with external quantum efficiencies (EQE) of around 5.5 %, we achieve a T50 > 5 h at 1000 mA·cm-2 at room temperature. The scaling-down approach and device architecture optimizations allowed for pulsed driving of the PeLEDs as short as 250 ns, reaching exceptionally large current densities above 5 kA·cm-2 and radiance values above 30000 W·m-2·sr-1.