We propose and test monolithic perovskite/CIGS tandem solar cells for readily stowable, ultra-lightweight space photovoltaics. We design operando and ex situ measurements to show that perovskite/CIGS tandem solar cells retain over 85% of their initial power-conversion efficiency after high-energy proton irradiation. While the perovskite sub-cell is unaffected after this bombardment, we identify increased non-radiative recombination in the CIGS bottom cell and nickel-oxide-based recombination layer. By contrast, monolithic perovskite/silicon-heterojunction cells degrade to 1% of their initial efficiency due to radiation-induced defects in silicon.

Mixed lead–tin halide perovskites have sufficiently low bandgaps (∼1.2 eV) to be promising absorbers for perovskite–perovskite tandem solar cells. Previous reports on lead–tin perovskites have typically shown poor optoelectronic properties compared to neat lead counterparts: short photoluminescence lifetimes (<100 ns) and low photoluminescence quantum efficiencies (<1%). Here, we obtain films with carrier lifetimes exceeding 1 μs and, through addition of small quantities of zinc iodide to the precursor solutions, photoluminescence quantum efficiencies under solar illumination intensities of 2.5%. The zinc additives also substantially enhance the film stability in air, and we use cross-sectional chemical mapping to show that this enhanced stability is because of a reduction in tin-rich clusters. By fabricating field-effect transistors, we observe that the introduction of zinc results in controlled p-doping. Finally, we show that zinc additives also enhance power conversion efficiencies and the stability of solar cells. Our results demonstrate substantially improved low-bandgap perovskites for solar cells and versatile electronic applications.

Perovskite-based tandem solar cells are of increasing interest as they approach commercialization. Here we use experimental parameters from optical spectroscopy measurements to calculate the limiting efficiency of perovskite–silicon and all-perovskite two-terminal tandems, employing currently available bandgap materials, as 42.0% and 40.8%, respectively. We show luminescence coupling between subcells (the optical transfer of photons from the high-bandgap to low-bandgap subcell) relaxes current matching when the high-bandgap subcell is a luminescent perovskite. We calculate that luminescence coupling becomes important at charge trapping rates (≤10 6 s –1 ) already being achieved in relevant halide perovskites. Luminescence coupling increases flexibility in subcell thicknesses and tolerance to different spectral conditions. For maximal benefit, the high-bandgap subcell should have the higher short-circuit current under average spectral conditions. This can be achieved by reducing the bandgap of the high-bandgap subcell, allowing wider, unstable bandgap compositions to be avoided. Lastly, we visualize luminescence coupling in an all-perovskite tandem through cross-section luminescence imaging.

cells, lasers, detectors, and light-emitting diodes (LEDs) owing to their exceptional optical and electronic properties such as long charge-carrier diffusion lengths, high absorption coefficients, tunable bandgaps, and facile processing. [1-4] For bulk polycrystalline perovskite thin films, one of the key approaches to boost the stability and optoelectronic properties is through employing mixtures of A-site cations, such as methylammonium (MA), formamidinium (FA), and cesium (Cs) [5,6] as well as mixtures of X-site anions, such as bromide (Br) and iodide (I). [7,8] Recently, rapid progress has been made in improving the performances of perovskite light-emitting diodes (PeLEDs), [9-14] yet their practical commercial implementation is still severely hindered by poor operational lifetimes. [10,15-19] Although the sensitivity of the devices to atmospheric effects such as oxygen and water can be mitigated through effective packaging techniques, [20] there is also an intrinsic instability in the devices with the high electric fields experienced under LED operation. [21] This instability appears to be caused by a combination of ionic migration and Joule heating, [20,22-26] which ultimately leads to degradation of the device performance. In order to overcome these degradation

Photon recycling has received increased attention in recent years following its observation in halide perovskites. It has been shown to lower the effective bimolecular recombination rate and thus increase excitation densities within a material. Here we introduce a general framework to quantify photon recycling which can be applied to any material. We apply our model to idealized solar cells and light-emitting diodes based on halide perovskites. By varying controllable parameters which affect photon recycling, namely thickness, charge trapping rate, non-ideal transmission at interfaces, and absorptance, we quantify the effect of each on photon recycling. In both device types, we demonstrate that maximizing absorption and emission processes remains paramount for optimizing devices, even if this is at the expense of photon recycling. Our results provide new insight into quantifying photon recycling in optoelectronic devices and demonstrate that photon recycling cannot always be seen as a beneficial process. Main Photon recycling has been reported in luminescent semiconductors including GaAs, InP and, more recently, halide perovskites such as methylammonium lead iodide (MAPbI3) [1-4]. It is a direct consequence of the reciprocity between absorption and emissionif a material can emit a photon at a wavelength it can also absorb a photon at that wavelength [5,6]. The role of photon recycling in decreasing radiative recombination rates in perovskites has been discussed [7,8]. Recently, Brenes et al. explored the effect of photon recycling on the maximum power point voltage in idealized perovskite solar cells with variable charge trapping rates [9] and demonstrated an increase in maximum power point voltage of 77 mV can be attributed to photon recycling. Similarly, Cho et al. recently showed photon recycling to be of importance in perovskite light-emitting diodes [4].

Halide perovskite/crystalline silicon (c-Si) tandem solar cells promise power conversion efficiencies beyond the limits of single-junction cells. However, the local light-matter interactions of the perovskite material embedded in this pyramidal multijunction configuration, and the effect on device performance, are not well understood. Here, we characterize the microscale optoelectronic properties of the perovskite semiconductor deposited on different c-Si texturing schemes. We find a strong spatial and spectral dependence of the photoluminescence (PL) on the geometrical surface constructs, which dominates the underlying grain-to-grain PL variation found in halide perovskite films. The PL response is dependent upon the texturing design, with larger pyramids inducing distinct PL spectra for valleys and pyramids, an effect which is mitigated with small pyramids. Further, optimized quasi-Fermi level splittings and PL quantum efficiencies occur when the c-Si large pyramids have had a secondary smoothing etch. Our results suggest that a holistic optimization of the texturing is required to maximize light in- and out-coupling of both absorber layers and there is a fine balance between the optimal geometrical configuration and optoelectronic performance that will guide future device designs.

A method for improving the efficiency of solar cells is combining a low-band-gap semiconductor with a singlet fission material (which converts one high-energy singlet into two low-energy triplets following photoexcitation). Here, we present a study of the interface between singlet fission molecules and low-band-gap halide pervoskites. We briefly present 150 experiments screening for triplet transfer into a halide perovskite. However, in all cases, triplet transfer was not observed. This motivated us to understand the halide perovskite–singlet fission interface better by carrying out first-principles calculations using tetracene and cesium lead iodide. We found that tetracene molecules/thin films preferentially orient themselves parallel to/perpendicular to the halide perovskite’s surface. This result is in agreement with simulations of tetracene (and other rodlike molecules) on a wide range of inorganic semiconductors. We present formation energies of all interfaces, which are significantly less favorable than for bulk tetracene, indicative of weak interaction at the interface. It was not possible to calculate excitonic states at the full interface due to computational limitations, so we instead present highly speculative toy interfaces between tetracene and a halide-perovskite-like structure. In these models, we focus on replicating tetracene’s electronic states correctly. We find that tetracene’s singlet and triplet energies are comparable to that of bulk tetracene, and the triplet is strongly localized on a single tetracene molecule, even at an interface. Our work provides new understanding of the interface between tetracene and halide perovskites, explores the potential for modeling excitons at interfaces, and begins to explain the difficulties in extracting triplets directly into inorganic semiconductors.

Recombination rates in optoelectronic semiconductors are typically recorded using timeintensive and expensive measurements. Here we present a method to extract decay rate ratios in a facile and rapid manner using only photoluminescence quantum efficiency measurements, which we demonstrate on halide perovskite thin film samples. We combine these ratios with time-resolved photoluminescence data to extract absolute recombination rates, with excellent agreement when our approach is benchmarked against the more time-and infrastructureintensive technique of transient absorption spectroscopy. This approach also enables direct quantification of the ratio between total second order and radiative second order recombination rates. We demonstrate that radiative recombination is only a fraction of total second order recombination in the range of halide perovskite samples relevant for photovoltaics. We showcase the implications of rapid extraction of decay rates by extracting decay rate ratios on a microscale and by calculating the expected maximum efficiency of a solar cell fabricated from the measured perovskite films. We show that reducing first order losses will significantly improve solar cell efficiency for our samples until time-resolved photoluminescence lifetimes are longer than ~ 1 µs (at low excitation pulse intensity), but at this point second order nonradiative recombination limits the efficiency of perovskite solar cells. This work represents a framework for rapidly screening optoelectronic semiconductors with techniques widely accessible to many research groups, identifies decay processes which would otherwise be missed, and directly relates the extracted values to predicted device performance metrics.