Search

The intriguing functionalities of emerging quasi-two-dimensional (2D) metal halide perovskites (MHPs) have led to further exploration of this material class for sustainable and scalable optoelectronic applications. However, the chemical complexities in precursors – primarily determined by the 2D:3D compositional ratio – result in uncontrolled phase heterogeneities in these materials, which compromises the optoelectronic performances. Yet, this phenomenon remains poorly understood due to the massive quasi-2D compositional space. To systematically explore the fundamental principles, herein, a high-throughput automated synthesis-characterization workflow is designed and implemented to formamidinium (FA)-based quasi-2D MHP system. It is revealed that the stable 3D-like phases, where the α-FAPbI3 surface is passivated by 2D spacer molecules, exclusively emerge at the compositional range (35-55% of FAPbI3), deviating from the stoichiometric considerations. A quantitative crystallographic study via high-throughput grazing-incidence wide-angle X-ray scattering (GIWAXS) experiments integrated with automated peak analysis function quickly reveals that the 3D-like phases are vertically aligned, facilitating vertical charge conduction that could be beneficial for optoelectronic applications. Together, this study uncovers the optimal 2D:3D compositional range for complex quasi-2D MHP systems, realizing desired optoelectronic performances and stability. The automated experimental workflow significantly accelerates materials discoveries and processing optimizations while providing fundamental insights into complex materials systems.

Preferred crystallographic orientation in polycrystalline films is desirable for efficient charge carrier transport in metal halide perovskites and semiconductors. However, the mechanisms that determine the preferred orientation of halide perovskites are still not well understood. In this work, we investigate crystallographic orientation in lead bromide perovskites. We show that the solvent of the precursor solution and organic A-site cation strongly affect the preferred orientation of the deposited perovskite thin films. Specifically, we show that the solvent, dimethylsulfoxide, influences the early stages of crystallization and induces preferred orientation in the deposited films by preventing colloidal particle interactions. Additionally, the methylammonium A-site cation induces a higher degree of preferred orientation than the formamidinium counterpart. We use density functional theory to show that the lower surface energy of the (100) plane facets in methylammonium-based perovskites, compared to the (110) planes, is the reason for the higher degree of preferred orientation. In contrast, the surface energy of the (100) and (110) facets is similar for formamidinium-based perovskites, leading to lower degree of preferred orientation. Furthermore, we show that different A-site cations do not significantly affect ion diffusion in bromine-based perovskite solar cells but impact ion density and accumulation, leading to increased hysteresis. Our work highlights the interplay between the solvent and organic A-site cation which determine crystallographic orientation and plays a critical role in the electronic properties and ionic migration of solar cells.

The impact of the bulky-cation-modified interfaces on halide perovskite solar cell stability is underexplored. In this work, the thermal instability of the bulky-cation interface layers used in the state-of-the-art solar cells is demonstrated. X-ray photoelectron spectroscopy and synchrotron-based grazing-incidence X-ray scattering measurements reveal significant changes in the chemical composition and structure at the surface of these films that occur under thermal stress. The changes impact charge-carrier dynamics and device operation, as shown in transient photoluminescence, excitation correlation spectroscopy, and solar cells. The type of cation used for surface treatment affects the extent of these changes, where long carbon chains provide more stable interfaces. These results highlight that prolonged annealing of the treated interfaces is critical to enable reliable reporting of performances and to drive the selection of different bulky cations.

Carlo A.R. Perini is a post-doctoral researcher at Georgia Institute of Technology, Energy Materials Lab. His studies focus on the development and understanding of interface passivation of 3D metal halide perovskites using vapor deposition routes. He has a PhD in Physics at Politecnico di Milano, in collaboration with the Italian Institute of Technology (IIT), focused on the study of energy efficient, scalable, and environmentally friendly deposition routes for lead halide perovskites. Tiarnan A. S. Doherty is a PhD student in the Cavendish laboratory at the University of Cambridge working on nanoscale structure property relationships in metal-halide perovskites. He received the gold graduate student award at the Fall Materials Research Society meeting. Samuel D. Stranks is a University Lecturer in Energy and Royal Society University Research Fellow at the University of Cambridge. His group's research focuses on the optical and electronic properties of emerging semiconductors for low-cost, transformative electronics applications including light-harvesting (e.g., photovoltaic) and light-emission (e.g., LED) devices. He received the 2018 Henry Moseley Award and Medal from the Institute of Physics, the 2019 Marlow Award from the Royal Society of Chemistry, and is a co-founder of Swift Solar, a startup developing lightweight perovskite PV panels. Juan-Pablo Correa-Baena is an Assistant Professor and Goizueta Junior Faculty Chair in the School of Materials Science and Engineering at Georgia Institute of Technology. His group focuses on the understanding and control of electronic dynamics at the nanoscale for low-cost semiconductors, such as halide perovskites. He completed his PhD at the University of Connecticut, followed by a postdoctoral fellowship at EPFL, Switzerland, then a US Department of Energy postdoctoral fellowship at MIT, USA. Robert L. Z. Hoye is a Lecturer (Assistant Professor) at Imperial College London. He leads the Energy Materials and Devices group, which is working on developing defect-tolerant semiconductors and their application in optoelectronic devices. This includes tandem photovoltaics, indoor solar cells, and light-emitting diodes. Robert has received the Young Engineer of the Year Award from the Royal Academy of Engineering, the Sir Henry Royce Medal from the Institution of Engineering and Technology, and the Rising Star Award from the Waterloo Institute for Nanotechnology.

The certified power conversion efficiency of state-of-the-art organic–inorganic hybrid perovskite solar cells has surpassed 25%, showing promising potential for commercialization. Compared with vol...

The commercial feasibility of perovskite solar cells (PSCs) is not guaranteed as long as lead (Pb) is present in the active material, halide perovskites. Mixed halide tin (Sn)-based alloyed perovsk...

Over the past decade, lead halide perovskite materials have emerged as a promising candidate for third-generation solar cells and have progressed extremely rapidly. The tunable band gap, strong absorption, high power conversion efficiency, and low cost of perovskite solar cells makes them highly competitive compared to current commercialized silicon-based and thin film-based photovoltaic technologies. However, commercial products unavoidably result in large amounts of waste and end-of-life devices which can cause serious environmental impacts. To address this issue, recycle and recovery technologies of perovskite solar cells should be researched and developed proactively. In this review, the development of perovskite solar cells and their necessary materials are first introduced. Subsequently, the potential environmental impacts of perovskite solar cells are discussed, including their stability and lifetime, use of critical materials (i.e., indium, tin, and lead), and toxicity. Accordingly, the present recycle and recovery technologies are reviewed, providing information and recommendations of key strategies for recycling and recovering. Finally, future works and strategies for recycling and recovering perovskite solar cells are proposed.

Metal halide perovskite solar cells (PSCs) are an emerging photovoltaic technology with the potential to disrupt the mature silicon solar cell market. Great improvements in device performance over the past few years, thanks to the development of fabrication protocols1-3, chemical compositions4,5 and phase stabilization methods6-10, have made PSCs one of the most efficient and low-cost solution-processable photovoltaic technologies. However, the light-harvesting performance of these devices is still limited by excessive charge carrier recombination. Despite much effort, the performance of the best-performing PSCs is capped by relatively low fill factors and high open-circuit voltage deficits (the radiative open-circuit voltage limit minus the high open-circuit voltage)11. Improvements in charge carrier management, which is closely tied to the fill factor and the open-circuit voltage, thus provide a path towards increasing the device performance of PSCs, and reaching their theoretical efficiency limit12. Here we report a holistic approach to improving the performance of PSCs through enhanced charge carrier management. First, we develop an electron transport layer with an ideal film coverage, thickness and composition by tuning the chemical bath deposition of tin dioxide (SnO2). Second, we decouple the passivation strategy between the bulk and the interface, leading to improved properties, while minimizing the bandgap penalty. In forward bias, our devices exhibit an electroluminescence external quantum efficiency of up to 17.2 per cent and an electroluminescence energy conversion efficiency of up to 21.6 per cent. As solar cells, they achieve a certified power conversion efficiency of 25.2 per cent, corresponding to 80.5 per cent of the thermodynamic limit of its bandgap.

One of the organic components in the perovskite photo-absorber, the methylammonium cation, has been suggested to be a roadblock to the long-term operation of organic–inorganic hybrid perovskite-based solar cells. In this work we systematically explore the crystallographic and optical properties of the compositional space of mixed cation and mixed halide lead perovskites, where formamidinium (FA+) is gradually replaced by cesium (Cs+), and iodide (I−) is substituted by bromide (Br−), i.e., CsyFA1−yPb(BrxI1−x)3. Higher tolerance factors lead to more cubic structures, whereas lower tolerance factors lead to more orthorhombic structures. We find that while some correlation exists between the tolerance factor and structure, the tolerance factor does not provide a holistic understanding of whether or not a perovskite structure will fully form. By screening 26 solar cells with different compositions, our results show that Cs1/6FA5/6PbI3 delivers the highest efficiency and long-term stability among the I-rich compositions. This work sheds light on the fundamental structure–property relationships in the CsyFA1−yPb(BrxI1−x)3 compositional space, providing vital insight to the design of durable perovskite materials. Our approach provides a library of structural and optoelectronic information for this compositional space.

This review focuses on the advancements in stability of perovskite solar cells under stress from ambient moisture, high temperatures, and UV light exposure. Moisture stability has been improved by utilizing several polymeric encapsulation methods, moisture-resistant hole transport layers (HTLs), CF4 plasma treatments, and perovskite grain crosslinking. Fluorinated encapsulation methods have proven especially successful, producing cells that maintained their PCE after 75 days at 50% RH and 5 mW cm−2 of UV radiation. Temperature destabilization has been hypothesized to occur as a result of perovskite phase transitions and the HTL dopant migration to the mesoporous TiO2 surface. Temperature-sensitive perovskites have been stabilized by tuning the Goldschmidt tolerance factor and introducing thermally resistant HTLs embedded in a polymeric matrix with polycarbonate acting as an effective thermal insulating matrix. UV light instabilities have also been shown to occur due to the photocatalysis of TiO2 and the TiO2 perovskite interface. The introduction of a Sb2S3 buffer or CsBr clusters as interface modifiers can stabilize the interface of TiO2 perovskite. Herein, we aim at highlighting the main processes that prevent perovskite degradation using polymers and interfacial modifiers.

Atomic layer deposition (ALD) allows for a great level of control over the thickness and stoichiometry of materials. ALD provides a suitable route to deposit lead halides, which can further be converted to perovskite for photovoltaics, photoemission, and photodetection, among other applications. Deposition of lead halides by ALD has already begun to be explored; however, the precursors used in published processes are highly hazardous, require expensive fabrication processes, or contain impurities that can jeopardize the optoelectronic properties of metal halide perovskites after conversion. We sought to deposit lead iodide (PbI2) by a facile ALD process involving only two readily accessible, low-cost precursors and without involving any unwanted impurities that could act as recombination centers once the PbI2 is later converted to perovskite. Crystalline PbI2 nanocrystals were grown on soda-lime glass (SLG), silicon dioxide support grids, and silicon wafer substrates and provide the groundwork for further investigation into developing lead halide perovskite processes by ALD. The ALD-grown PbI2 was characterized by annular dark field scanning transmission electron microscopy (ADF-STEM), atomic force microscopy (AFM), and x-ray photoemission spectroscopy (XPS), among other methods. This work presents the first step to synthesize lead halide perovskites with atomic control for applications such as interfacial layers in photovoltaics and for deposition in microcavities for lasing.

et al., Large datasets are now ubiquitous as technology enables higher-throughput experiments, but rarely can a research field truly benefit from the research data generated due to inconsistent formatting, undocumented storage or improper dissemination. Here we extract all the meaningful device data from peer-reviewed papers on metal-halide perovskite solar cells published so far and make them available in a database. We collect data from over 42,400 photovoltaic devices with up to 100 parameters per device. We then develop open-source and accessible procedures to analyse the data, providing examples of insights that can be gleaned from the analysis of a large dataset. The database, graphics and analysis tools are made available to the community and will continue to evolve as an open-source initiative. This approach of extensively capturing the progress of an entire field, including sorting, interactive exploration and graphical representation of the data, will be applicable to many fields in materials science, engineering and biosciences., Open access funding provided by Helmholtz-Zentrum Berlin für Materialien und Energie GmbH., The core funding of the project has been received from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 787289. We acknowledge the following sources for individual funding. Cambridge India Ramanujan Scholarship, China Scholarship Council, Deutscher Akademischer Austauschdienst (DAAD), EPSRC (grant no. EP/S009213/1), European Union’s Horizon 2020 research and innovation programme (grant no. 764787, EU Project ‘MAESTRO’), (grant no. 756962, ERC Project ‘HYPERION’), (grant no. 764047, EU Project ‘ESPResSo’ and grant no. 850937), GCRF/EPSRC SUNRISE (EP/P032591/1), German Federal Ministry for Education and Research (BMBF), HyPerFORME, NanoMatFutur (grant no. 03XP0091). PEROSEED (ZT-0024), Helmholtz Energy Materials Foundry, The Helmholtz Innovation Laboratory HySPRINT. BMBF (grant nos. 03SF0540, 03SF0557A), HyPerCells graduate school, Helmholtz Association, Helmholtz International Research School (HI-SCORE), the Erasmus programme (CDT-PV, grant no. EP/L01551X/1), the European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie grant agreement nos. 841386, 795079 and 840751), Royal Society University Research Fellowship (grant no. UF150033). SNaPSHoTs (BMBF), SPARC II, German Research Foundation (DFG, grant no. SPP2196), The National Natural Science Foundation of China (grant no. 51872014), the Recruitment Programme of Global Experts, Fundamental Research Funds for the Central Universities and the ‘111’ project (grant no. B17002), the US Department of Energy’s Office of Energy Efficiency and Renewable Energy under Solar Energy Technologies Office (SETO) agreement no. DE-EE0008551, the Colombia Scientific Programme in the framework of the call Ecosistema Cientifíco (Contract no. FP44842-218-2018), the committee for the development of research (CODI) of the Universidad de Antioquia (grant no. 2017-16000), Spanish MINECO (Severo Ochoa programme, grant no. SEV‐2015‐0522), the Swedish research council (VR, grant no. 2019-05591) and the Swedish Energy Agency (grant no. 2020-005194).

The exploration of the compositional space of halide perovskites is prohibitively costly using traditional experimental research strategies. Sun and colleagues demonstrated a physics-informed, machine-learning-guided, experimental approach that overturns this limitation enabling a rapid and efficient maximization of stability in mixed-cation perovskites.

One of the organic component in the perovskite photo-absorber, the methylammonium cation, has been suggested to be a roadblock to long-term operation of organic-inorganic hybrid perovskite-based solar cells. Methylammonium-free perovskites thus represent a possible direction for more stable photo-absorbers that are also compatible with multijunction solar cells. However, most work on methylammonium-free perovskites involves cesium and formamidinium as the A-site cations, which are thermodynamically less stable than the methylammonium-based materials. In this work we systematically explore the crystallographic and optical properties of the compositional space of mixed cation and mixed halide lead perovskites, where formamidinium (FA+) is gradually replaced by cesium (Cs+), and iodide (I-) is substituted by bromide (Br-), i.e., CsyFA1–yPb(BrxI1–x)3. The crystal phases, which could be tuned by changing the tolerance factor for mixed perovskite alloys, are qualitatively determined and the composition–structure relationship is established in the CsyFA1–yPb(BrxI1–x)3 compositional space. We find that higher tolerance factors lead to more cubic structures, whereas lower tolerance factors lead to more orthorhombic. We also find that while some correlation exists between tolerance factor and structure, tolerance factor does not provide a holistic understanding of whether a perovskite structure will fully form. Given the wide range of bandgaps produced by this compositional space, an empirical expression is devised to predict the optical bandgap of CsyFA1–yPb(BrxI1–x)3 perovskites – which changes as a function of composition –, conducive to the design of absorbers with bandgaps tailor-made for specific tandem and single-junction applications. By screening 26 solar cells with different compositions, we find that Cs1/6FA5/6PbI3 delivers the highest efficiency and long-term stability among I-rich compositions. This work sheds light on the fundamental structure-property relationships in the CsyFA1–yPb(BrxI1–x)3 compositional space, providing vital insight to the design of durable perovskite materials. Our approach provides a library of structural and optoelectronic information of this compositional space.

One of the organic component in the perovskite photo-absorber, the methylammonium cation, has been suggested to be a roadblock to long-term operation of organic-inorganic hybrid perovskite-based solar cells. Methylammonium-free perovskites thus represent a possible direction for more stable photo-absorbers that are also compatible with multijunction solar cells. However, most work on methylammonium-free perovskites involves cesium and formamidinium as the A-site cations, which are thermodynamically less stable than the methylammonium-based materials. In this work we systematically explore the crystallographic and optical properties of the compositional space of mixed cation and mixed halide lead perovskites, where formamidinium (FA+) is gradually replaced by cesium (Cs+), and iodide (I-) is substituted by bromide (Br-), i.e., CsyFA1–yPb(BrxI1–x)3. The crystal phases, which could be tuned by changing the tolerance factor for mixed perovskite alloys, are qualitatively determined and the composition–structure relationship is established in the CsyFA1–yPb(BrxI1–x)3 compositional space. We find that higher tolerance factors lead to more cubic structures, whereas lower tolerance factors lead to more orthorhombic. We also find that while some correlation exists between tolerance factor and structure, tolerance factor does not provide a holistic understanding of whether a perovskite structure will fully form. Given the wide range of bandgaps produced by this compositional space, an empirical expression is devised to predict the optical bandgap of CsyFA1–yPb(BrxI1–x)3 perovskites – which changes as a function of composition –, conducive to the design of absorbers with bandgaps tailor-made for specific tandem and single-junction applications. By screening 26 solar cells with different compositions, we find that Cs1/6FA5/6PbI3 delivers the highest efficiency and long-term stability among I-rich compositions. This work sheds light on the fundamental structure-property relationships in the CsyFA1–yPb(BrxI1–x)3 compositional space, providing vital insight to the design of durable perovskite materials. Our approach provides a library of structural and optoelectronic information of this compositional space.

The impact on device stability of the bulky cation-modified interfaces in halide perovskite solar cells is not well-understood. We demonstrate the thermal instability of the bulky cation interface layers used in some of the highest performing solar cells to date. X-ray photoelectron spectroscopy and synchrotron-based grazing incidence X-ray scattering measurements reveal significant changes under thermal stress in the chemical composition and structure at the surface of these films. The changes impact charge carrier dynamics and device operation, as shown in transient photoluminescence, excitation correlation spectroscopy, and solar cells. The type of cation used for passivation affects the extent of these changes, where long carbon chains provide more stable interfaces and thus longer durability (more than 1000 hrs at 55ºC). Such findings highlight that annealing the treated interfaces before characterization is critical to enable reliable reporting of performances and to drive the selection between different cations.

Perovskite solar cells have been at the center of intense research over the past decade. Efficiencies have gone from single digits to a certified 25.2%, an unprecedented improvement for any solar cell technology. At this stage, stability remains a concern regarding the suitability of these solar cells for commercialization. Here, we review recent developments in the use of carbon materials to improve the stability of perovskite solar cells. Incorporating carbon materials into perovskite solar cells promises to be revolutionary in the solar cell field, as degradation mechanisms are alleviated to achieve long-term stability making them attractive for commercialization.

Summary We investigate the rubrene triplet sensitization by perovskite thin films based on methylammonium formamidinium lead triiodide (MAFA) of varying thicknesses. The power-law dependence of both the MAFA photoluminescence (PL) intensity and upconverted emission is tracked as a function of the incident power density. Bimolecular triplet-triplet annihilation (TTA) exhibits a unique power-law dependence with a slope change from quadratic-to-linear at the threshold Ith. The underlying MAFA PL power-law dependence dictates the power law of the upconverted PL: (1) below Ith, the slope of the upconverted PL is twice the value of the MAFA PL; (2) above Ith, it follows the same power law as the underlying recombination of mobile electrons and holes in the MAFA films. We find that the Ith shifts to subsolar incident laser powers when increasing the MAFA thickness above 30 nm. For the thickest MAFA film of 380 nm we find an upconversion threshold of Ith = 7.1 mW/cm2.

Summary Accelerating the experimental cycle for new materials development is vital for addressing the grand energy challenges of the 21st century. We fabricate and characterize 75 unique perovskite-inspired compositions within a 2-month period, with 87% exhibiting band gaps between 1.2 and 2.4 eV, which are of interest for energy-harvesting applications. We utilize a fully connected deep neural network to classify compounds based on experimental X-ray diffraction data into 0D, 2D, and 3D structures, more than 10 times faster than human analysis and with 90% accuracy. We validate our methods using lead-halide perovskites and extend the application to lead-free compositions. The wider synthesis window and faster cycle of learning enables the realization of a multi-site lead-free alloy series, Cs3(Bi1-xSbx)2(I1-xBrx)9. We reveal the non-linear band-gap behavior and transition in dimensionality upon simultaneous alloying on the B-site and X-site of Cs3Bi2I9 with Sb and Br.

The mechanism and elemental composition that form the basis for the improved optical and electronic properties in mixed-ion lead halide perovskite solar cells are still not well understood compared...

The role electron-transport layers (ETLs) play in perovskite solar cells (PSCs) is still widely debated. Conduction band alignment at the perovskite/ETL interface has been suggested to be an import...

Perovskite solar cells promise to yield efficiencies beyond 30% by improving the quality of the materials and devices. Electronic defect passivation and suppression of detrimental charge-carrier recombination has been used as a strategy to achieve high performance perovskite solar cells. This strategy often relies on interlayers that may also hinder carrier transfer across interfaces. In addition to interfacial charge transport, very little is known about the role of crystallographic structure on charge carrier transport through the bulk of the material. In this presentation, I will discuss how different crystallographic phases of the perovskite affect charge carrier transport. Interfacial transport across interfaces will be further studied to understand whether crystalline structures or amorphous phases are able to efficiently allow transport out the device. Synchrotron-based characterization techniques, such as grazing incidence x-ray spectroscopy and x-ray fluorescence will be used to understand the structural and chemical composition of the films, whereas intensity-modulated photocurrent spectroscopy will be used to understand transport processes in the devices. We show that the orthorhombic phase of the methylammonium lead iodide perovskite forms along with the tetragonal phase and hinders carrier transport and thus short circuit currents. We also show that the crystal structure of the 2D perovskite used as an interlayer in the perovskite solar cell is crucial to efficient charge extraction.

Halide perovskites are a strong candidate for the next generation of photovoltaics. Chemical doping of halide perovskites is an established strategy to preparethe highest efficiency andmost stable perovskite-based solar cells. In this study, we unveil the doping mechanism of halide perovskites using a series of alkaline earth metals. We find that low doping levels enable the incorporation of the dopant within the perovskite lattice, whereas high doping concentrations induce surface segregation. The threshold from low to high doping regime correlates to the size of the doping element. We show that the low doping regime results in a more n-typematerial, while the high doping regime induces a less n-type doping character. Our work provides a comprehensive picture of the unique doping mechanism of halide perovskites, which differs fromclassical semiconductors. We proved the effectiveness of the low doping regime for the first time, demonstrating highly efficient methylammonium lead iodide based solar cells in both n-i-p and p-i-n architectures.

The impact on device stability of the bulky cation-modified interfaces in halide perovskite solar cells is not well-understood. We demonstrate the thermal instability of the bulky cation interface layers used in some of the highest performing solar cells to date. X-ray photoelectron spectroscopy and synchrotron-based grazing incidence X-ray scattering measurements reveal significant changes under thermal stress in the chemical composition and structure at the surface of these films. The changes impact charge carrier dynamics and device operation, as shown in transient photoluminescence, excitation correlation spectroscopy, and solar cells. The type of cation used for passivation affects the extent of these changes, where long carbon chains provide more stable interfaces and thus longer durability (more than 1000 hrs at 55oC). Such findings highlight that annealing the treated interfaces before characterization is critical to enable reliable reporting of performances and to drive the selection between different cations.

Here we highlight 35 researchers approximately under the age of 35. Age, of course, is just a number—our target was emerging early-career academics. Contributors were recruited in a self-propagating “pay-it-forward” manner, with each invitee being suggested by a peer who had already contributed. The final collection is an inspiring look at the challenges the current generation of materials researchers are tackling.

A small amount of alkali metals goes a long way toward improving hybrid perovskites for hot carrier solar cells., Successful implementation of hot carrier solar cells requires preserving high carrier temperature as carriers migrate through the active layer. Here, we demonstrated that addition of alkali cations in hybrid organic-inorganic lead halide perovskites led to substantially elevated carrier temperature, reduced threshold for phonon bottleneck, and enhanced hot carrier transport. The synergetic effects from the Rb, Cs, and K cations result in ~900 K increase in the effective carrier temperature at a carrier density around 1018 cm−3 with an excitation 1.45 eV above the bandgap. In the doped thin films, the protected hot carriers migrate 100 s of nanometers longer than the undoped sample as imaged by ultrafast microscopy. We attributed these improvements to the relaxation of lattice strain and passivation of halide vacancies by alkali cations based on x-ray structural characterizations and first principles calculations.

Degradation due to electron beam exposure has posed a challenge in the use of electron microscopy to probe halide perovskite materials and devices. In this study, the interaction between the electron beam and the perovskite across acceleration voltages and at low probe currents is investigated in a scanning electron microscope (SEM) by monitoring the electron-beam-induced current (EBIC) response in perovskite solar cells in a plan-view configuration. SEM probe conditions are identified where dozens of repeated scans over a single region of the perovskite solar cell induce minimal electronic degradation. Overall, the induced current response of the perovskite device is found to strongly depend upon the beam condition: Rapid decay occurs at high beam powers, the current activates at the lowest beam powers, and a newfound quasi-steady response is revealed at intermediate beam conditions. A quantitative window for the successful conduction of e-beam studies with minimal electronic degradation is revealed by evaluating induced current response over a wide range of perovskite devices, which invites broader use of SEM-based characterization techniques, including EBIC, as powerful techniques for correlative microscopy investigations.

Summary Perovskite solar cells (PSCs) are one of the emerging solar cell technologies with high conversion efficiency. Several deposition methods had been applied for preparing their hole transport layer (HTL). However, there are few direct evidences to demonstrate whether HTL and its interfaces in PSCs have been influenced by the deposition methods. In this study, the 3D morphology of PSCs has been reconstructed by focused ion beam-scanning electron microscopy from the PSCs in which HTLs are deposited by different methods. The compositional distribution of HTLs is unveiled as well. All these associated layers and interfaces display obvious morphological and compositional differences that are attributed to the HTL components’ solubility differences in the precursor solvent. Our investigation demonstrates the PSCs that HTL fabricated by dynamic spin-coating method have higher efficiency, better film uniformity, and less interfacial roughness than the static spin-coating-based devices.