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The lack of thermal stability of perovskite solar cells is hindering the progress of this technology towards adoption in the consumer market. Different pathways of thermal degradation are activated at different temperatures in these complex nanostructured hybrid composites. Thus, it is essential to explore the thermal response of the mesosuperstructured composite device to engineer materials and operating protocols. Here we produce devices according to four well-established recipes, and characterize their photovoltaic performance as they are heated within the operational range. The devices are analysed using transmission electron microscopy as they are further heated in situ , to monitor changes in morphology and chemical composition. We identify mechanisms for structural and chemical changes, such as iodine and lead migration, which appear to be correlated to the synthesis conditions. In particular, we identify a correlation between exposure of the perovskite layer to air during processing and elemental diffusion during thermal treatment. The thermal degradation of perovskite solar cells is an obstacle to their commercialization. Now, the mechanisms for thermally induced structural and chemical changes are identified by in situ measurements in a transmission electron microscope.

Fully printed wearable electronics based on two-dimensional (2D) material heterojunction structures also known as heterostructures, such as field-effect transistors, require robust and reproducible printed multi-layer stacks consisting of active channel, dielectric and conductive contact layers. Solution processing of graphite and other layered materials provides low-cost inks enabling printed electronic devices, for example by inkjet printing. However, the limited quality of the 2D-material inks, the complexity of the layered arrangement, and the lack of a dielectric 2D-material ink able to operate at room temperature, under strain and after several washing cycles has impeded the fabrication of electronic devices on textile with fully printed 2D heterostructures. Here we demonstrate fully inkjet-printed 2D-material active heterostructures with graphene and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet-printed flexible and washable field-effect transistors on textile, reaching a field-effect mobility of ~91 cm 2  V −1  s −1 , at low voltage (<5 V). This enables fully inkjet-printed electronic circuits, such as reprogrammable volatile memory cells, complementary inverters and OR logic gates. Heterojunction structures based on 2D materials show promise for wearable and textile electronics. Here, the authors demonstrate fully inkjet-printed hetero junctions of graphene and h-BN as a platform for FET-based smart electronics on wearable and washable textile substrates.

Over the last few years organic - inorganic halide perovskite-based solar cells have exhibited a rapid evolution, reaching certified power conversion efficiencies now surpassing 20%. Nevertheless the understanding of the optical and electronic properties of such systems on the nanoscale is still an open problem. In this work we investigate two model perovskite systems (based on iodine - CH3NH3PbI3 and bromine - CH3NH3PbBr3), analysing the local elemental composition and crystallinity and identifying chemical inhomogeneities.

Hybrid solar cells based on 1,2 methanofullerene (C61) capped CdSe and poly (3-hexylthiophene) (P3HT) were been investigated through a range of techniques. High resolution transmission electron microscopy (HRTEM) was used to characterize size, morphology and crystal structure of as-grown and C61-capped CdSe quantum dots. Cross sectional lamellar specimens were prepared from full photovoltaic devices using a focused ion beam milling approach. The sections were analysed by high angle annular dark field imaging in scanning TEM mode to determine the morphology of the device, in particular the intermixing of P3HT and capped quantum dots.

Hybrid solar cells based on 1,2 methanofullerene (C sub(61)) capped CdSe and poly (3-hexylthiophene) (P3HT) were been investigated through a range of techniques. High resolution transmission electron microscopy (HRTEM) was used to characterize size, morphology and crystal structure of as-grown and C sub(61)-capped CdSe quantum dots. Cross sectional lamellar specimens were prepared from full photovoltaic devices using a focused ion beam milling approach. The sections were analysed by high angle annular dark field imaging in scanning TEM mode to determine the morphology of the device, in particular the intermixing of P3HT and capped quantmn dots.

Interface engineering through passivating agents, in the form of organic molecules, is a powerful strategy to enhance the performance of perovskite solar cells. Despite its pivotal function in the development of a rational device optimization, the actual role played by the incorporation of interfacial modifications and the interface physics therein remains poorly understood. Here, we investigate the interface and device physics, quantifying charge recombination and charge losses in state-of-the-art inverted solar cells with power conversion efficiency beyond 23% - among the highest reported so far - by using multidimensional photoluminescence imaging. By doing that we extract physical parameters such as quasi-Fermi level splitting (QFLS) and Urbach energy enabling us to assess that the main passivation mechanism affects the perovskite/PCBM ([6,6]-phenyl-C 61 -butyric acid methyl ester) interface rather than surface defects. In this work, by linking optical, electrical measurements and modelling we highlight the benefits of organic passivation, made in this case by phenylethylammonium (PEAI) based cations, in maximising all the photovoltaic figures of merit. In this work, charge recombination and losses in inverted solar cells with dual organic cations interfacial passivation are quantified by mapping physical parameters obtained via continuous wave and time resolved photoluminescence imaging techniques.

The development of high efficiency solar cells relies on the management of electronic and optical properties that need to be accurately measured. As the conversion efficiencies increase, there is a concomitant electronic and photonic contribution that affects the overall performances. Here we show an optical method to quantify several transport properties of semiconducting materials and the use of multidimensional imaging techniques allows decoupling and quantifying the electronic and photonic contributions. Example of application is shown on halide perovskite thin film for which a large range of transport properties is given in the literature. We therefore optically measure pure carrier diffusion properties and evidence the contribution of optical effects such as the photon recycling as well as the photon propagation where emitted light is laterally transported without being reabsorbed. This latter effect has to be considered to avoid overestimated transport properties such as carrier mobility, diffusion length or diffusion coefficient. The electronic and photonic contributions to the power conversion efficiency in solar cell devices are often hard to disentangle. Here Bercegol et al. develop a purely optical method to quantitatively decouple and assess the electronic and photonic processes in halide perovskite solar cells.

Modifying the surfaces and grain boundaries of perovskites with passivating potassium halide layers can mitigate non-radiative losses and photoinduced ion migration, increasing luminescence yields and improving charge transport and interfaces with device electrodes. Potassium passivation improves perovskite luminescence Metal halide perovskites have excellent optoelectronic properties and are cheap and easy to manufacture, making them potential rivals for leading optoelectronic technologies. Solar cells are one promising direction, with efficiencies greater than 20% already achieved within just a few years. Despite this, luminescence yields in state-of-the-art perovskite solar cells are still far below 100%, so there is room for improvement. Samuel Stranks and colleagues decorate the surfaces and grain boundaries of perovksites with passivating potassium halide layers. This reduced parasitic non-radiative losses and photo-induced ion migration—two key causes of low luminescence yields. They applied this approach to a wide range of mixed halide perovskites, which not only yielded luminescence approaching the efficiency limits, but also improved the charge transport and interfaces with device electrodes. Metal halide perovskites are of great interest for various high-performance optoelectronic applications 1 . The ability to tune the perovskite bandgap continuously by modifying the chemical composition opens up applications for perovskites as coloured emitters, in building-integrated photovoltaics, and as components of tandem photovoltaics to increase the power conversion efficiency 2 , 3 , 4 . Nevertheless, performance is limited by non-radiative losses, with luminescence yields in state-of-the-art perovskite solar cells still far from 100 per cent under standard solar illumination conditions 5 , 6 , 7 . Furthermore, in mixed halide perovskite systems designed for continuous bandgap tunability 2 (bandgaps of approximately 1.7 to 1.9 electronvolts), photoinduced ion segregation leads to bandgap instabilities 8 , 9 . Here we demonstrate substantial mitigation of both non-radiative losses and photoinduced ion migration in perovskite films and interfaces by decorating the surfaces and grain boundaries with passivating potassium halide layers. We demonstrate external photoluminescence quantum yields of 66 per cent, which translate to internal yields that exceed 95 per cent. The high luminescence yields are achieved while maintaining high mobilities of more than 40 square centimetres per volt per second, providing the elusive combination of both high luminescence and excellent charge transport 10 . When interfaced with electrodes in a solar cell device stack, the external luminescence yield—a quantity that must be maximized to obtain high efficiency—remains as high as 15 per cent, indicating very clean interfaces. We also demonstrate the inhibition of transient photoinduced ion-migration processes across a wide range of mixed halide perovskite bandgaps in materials that exhibit bandgap instabilities when unpassivated. We validate these results in fully operating solar cells. Our work represents an important advance in the construction of tunable metal halide perovskite films and interfaces that can approach the efficiency limits in tandem solar cells, coloured-light-emitting diodes and other optoelectronic applications.

This study explores the potential of Cu(In,Ga)Se2 (CIGS) absorbers, commonly used in high-efficiency solar cells, as photocathodes to improve solar-to-fuel conversion efficiency. CIGS’s exceptional light absorption, tunable band gaps, and stability make it an ideal candidate for this application. We examined the performance of bare CIGS and CIGS|CdS pn junctions in photoelectrochemical (PEC) CO2 reduction, emphasizing the crucial role of interface engineering. Additionally, we assessed the impact of additional ultra-thin functional oxide layers (TiO2, NiO, Al2O3, and SnO2) and inorganic nanostructured co-catalysts (ZnO and Cu2O). Our findings reveal that while bare CIGS can reduce CO2 to CO, the introduction of a pn junction significantly enhances current density and selectivity. A well-optimized photoelectrode based on a CIGS|CdS pn junction can achieve remarkable performance despite its instability, attaining up to 98.5% CO2 reduction selectivity and photocurrent densities of approximately 8 mA cm–2 at –1.3 V vs SCE under 1-sun illumination. However, protective layers, while improving stability, often led to decreased photocurrent. These insights highlight that combining CIGS absorber layers with appropriate charge transport and catalytic layers is essential for developing efficient and stable PEC systems for CO2 reduction.