The structural phases and optoelectronic properties of coevaporated CsPbI3 thin films with a wide range of CsI/PbI2 compositional ratios are investigated using high throughput experimentation and ...gradient samples. It is found that for CsI‐rich growth conditions, CsPbI3 can be synthesized directly at low temperature into the distorted perovskite γ‐CsPbI3 phase without detectable secondary phases. In contrast, PbI2‐rich growth conditions are found to lead to the non‐perovskite δ‐phase. Photoluminescence spectroscopy and optical‐pump THz‐probe mapping show carrier lifetimes larger than 75 ns and charge carrier (sum) mobilities larger than 60 cm2 V−1 s−1 for the γ‐phase, indicating their suitability for high efficiency solar cells. The dependence of the carrier mobilities and luminescence peak energy on the Cs‐content in the films indicates the presence of Schottky defect pairs, which may cause the stabilization of the γ‐phase. Building on these results, p–i–n type solar cells with a maximum efficiency exceeding 12% and high shelf stability of more than 1200 h are demonstrated, which in the future could still be significantly improved, judging on their bulk optoelectronic properties.
Stable inorganic perovskite CsPbI3 thin films and solar cells are obtained by low temperature vacuum deposition without the need for high‐temperature annealing steps. Intentional compositional gradients on the samples allow combinatorial evaluation of structure‐property relationships using high‐throughput experimentation techniques, indicating that the perovskite phase is stable for Cs‐rich conditions. Solar cells with efficiency > 12% are demonstrated.
Perovskite solar cells (PSC) have shown that under laboratory conditions they can compete with established photovoltaic technologies. However, controlled laboratory measurements usually performed do ...not fully resemble operational conditions and field testing outdoors, with day‐night cycles, changing irradiance and temperature. In this contribution, the performance of PSCs in the rooftop field test, exposed to real weather conditions is evaluated. The 1 cm2 single‐junction devices, with an initial average power conversion efficiency of 18.5% are tracked outdoors in maximum power point over several weeks. In parallel, irradiance and air temperature are recorded, allowing us to correlate outside factors with generated power. To get more insight into outdoor device performance, a comprehensive set of laboratory measurements under different light intensities (10% to 120% of AM1.5) and temperatures is performed. From these results, a low power temperature coefficient of −0.17% K−1 is extracted in the temperature range between 25 and 85 °C. By incorporating these temperature‐ and light‐dependent PV parameters into the energy yield model, it is possible to correctly predict the generated energy of the devices, thus validating the energy yield model. In addition, degradation of the tested devices can be tracked precisely from the difference between measured and modelled power.
In this paper, laboratory and rooftop performance of perovskite solar cells under changing temperature and irradiance is analyzed. By integrating laboratory data trends and measured weather data into optical energy yield model, the temperature‐dependent energy yield model is developed and validated, and can be used to predict generated energy of perovskite solar cells or track their degradation during field testing.
Formamidinium iodide (FAI) based perovskite absorbers have been shown to be ideal candidates for highly efficient and operationally stable perovskite solar cells (PSC). A major challenge for ...formamidinium lead iodide (FAPbI3) is to suppress the phase transition from the photoactive black phase into yellow nonperovskite δ‐phase. Several approaches to stabilize the black phase have been developed for solution‐based perovskites, whereas so far, vacuum‐deposited FAPbI3 has rarely been reported. This study demonstrates the preparation of FAPbI3 by co‐evaporation and discusses the influence of the subjacent hole transporting layer (HTL) on its phase stability. By using FAI excess in the evaporation process in combination with phosphonic acids groups from the HTL, the black perovskite phase is stabilized at room temperature. Further addition of 32–59% methylammonium iodide (MAI) during the co‐evaporation process leads to good absorption properties and high PSC efficiencies of 20.4%. In addition, excellent stability is achieved for optimized MAI to FAI ratios, maintaining 100% of the initial PSC performance after 1000 h under constant operation. This highly stable perovskite composition enables the first monolithic fully textured perovskite/silicon tandem solar cells with co‐evaporated perovskite absorbers. Due to the conformally covered pyramid texture, these tandem cells show minimal reflection losses and reach an efficiency of 24.6%.
Co‐evaporation methylammonium formamidinium lead iodide perovskites are investigated and different aspects of stability are addressed. The influence of the perovskite composition on the performance and the long‐term stability of the resulting solar cells is studied. Monolithic fully textured perovskite/silicon tandem solar cells with co‐evaporated perovskite absorber are realized. These tandem cells reach an efficiency of 24.6% and exhibit minimal reflection losses.
The unprecedented emergence of perovskite‐based solar cells (PSCs) has been accompanied by an intensive search of suitable materials for charge‐selective contacts. For the first time a ...hole‐transporting self‐assembled monolayer (SAM) as the dopant‐free hole‐selective contact in p–i–n PSCs is used and a power conversion efficiency of up to 17.8% with average fill factor close to 80% and undetectable parasitic absorption is demonstrated. SAM formation is achieved by simply immersing the substrate into a solution of a novel molecule V1036 that binds to the indium tin oxide surface due to its phosphonic anchoring group. The SAM and its modifications are further characterized by Fourier‐transform infrared and vibrational sum‐frequency generation spectroscopy. In addition, photoelectron spectroscopy in air is used for measuring the ionization potential of the studied SAMs. This novel approach is also suitable for achieving a conformal coverage of large‐area and/or textured substrates with minimal material consumption and can potentially be extended to serve as a model system for substrate‐based perovskite nucleation and passivation control. Further gains in efficiency can be expected upon SAM optimization by means of molecular and compositional engineering.
A novel concept for the formation of the hole selective layer in efficient perovskite solar cells is presented. Carbazole‐based material is synthesized and used for the formation of a self‐assembled monolayer on top of the indium tin oxide transparent conductive substrate. Power conversion efficiency as high as 17.8% is achieved.
Halide perovskites are emerging as revolutionary materials for optoelectronics. Their ionic nature and the presence of mobile ionic defects within the crystal structure have a dramatic influence on ...the operation of thin‐film devices such as solar cells, light‐emitting diodes, and transistors. Thin films are often polycrystalline and it is still under debate how grain boundaries affect the migration of ions and corresponding ionic defects. Laser excitation during photoluminescence (PL) microscopy experiments leads to formation and subsequent migration of ionic defects, which affects the dynamics of charge carrier recombination. From the microscopic observation of lateral PL distribution, the change in the distribution of ionic defects over time can be inferred. Resolving the PL dynamics in time and space of single crystals and thin films with different grain sizes thus, provides crucial information about the influence of grain boundaries on the ionic defect movement. In conjunction with experimental observations, atomistic simulations show that defects are trapped at the grain boundaries, thus inhibiting their diffusion. Hence, with this study, a comprehensive picture highlighting a fundamental property of the material is provided while also setting a theoretical framework in which the interaction between grain boundaries and ionic defect migration can be understood.
The study presents the curious case of ionic defect migration in halide perovskites. Using photoluminescence in samples of different grain sizes coupled with molecular dynamic simulation, this study highlights the light‐induced ionic defect movement in relation to the material microstructure. In particular, it is shown that ionic defect migration is blocked by grain boundaries in methylammonium lead iodide perovskite.
The fullerene C60 is commonly applied as the electron transport layer in high‐efficiency metal halide perovskite solar cells and has been found to limit their open circuit voltage. Through ...ultra‐sensitive near‐UV photoelectron spectroscopy in constant final state mode (CFSYS), with an unusually high probing depth of 5–10 nm, the perovskite/C60 interface energetics and defect formation is investigated. It is demonstrated how to consistently determine the energy level alignment by CFSYS and avoid misinterpretations by accounting for the measurement‐induced surface photovoltage in photoactive layer stacks. The energetic offset between the perovskite valence band maximum and the C60 HOMO‐edge is directly determined to be 0.55 eV. Furthermore, the voltage enhancement upon the incorporation of a LiF interlayer at the interface can be attributed to originate from a mild dipole effect and probably the presence of fixed charges, both reducing the hole concentration in the vicinity of the perovskite/C60 interface. This yields a field effect passivation, which overcompensates the observed enhanced defect density in the first monolayers of C60.
Field effect passivation is identified as the origin of the voltage enhancement upon inserting a LiF interlayer at the electron selective contact of perovskite solar cells by high sensitivity near‐UV photoelectron spectroscopy. LiF increases the defect density in the C60, however, the minority charge carrier density in the vicinity of the interface is lowered, resulting in an overall reduction in the non‐radiative recombination.
The performance of five hole‐transporting layers (HTLs) is investigated in both single‐junction perovskite and Cu(In, Ga)Se2 (CIGSe)‐perovskite tandem solar cells: nickel oxide (NiOx,), copper‐doped ...nickel oxide (NiOx:Cu), NiOx+SAM, NiOx:Cu+SAM, and SAM, where SAM is the 2‐(3,‐6Dimethoxy‐9H‐carbazol‐9yl)ethylphosphonic acid (MeO‐2PACz) self‐assembled monolayer. The performance of the devices is correlated to the charge‐carrier dynamics at the HTL/perovskite interface and the limiting factors of these HTLs are analyzed by performing time‐resolved and absolute photoluminescence ((Tr)PL), transient surface photovoltage (tr‐SPV), and X‐ray/UV photoemission spectroscopy (XPS/UPS) measurements on indium tin oxide (ITO)/HTL/perovskite and CIGSe/HTL/perovskite stacks. A high quasi‐Fermi level splitting to open‐circuit (QFLS‐Voc) deficit is detected for the NiOx‐based devices, attributed to electron trapping and poor hole extraction at the NiOx‐perovskite interface and a low carrier effective lifetime in the bulk of the perovskite. Simultaneously, doping the NiOx with 2% Cu and passivating its surface with MeO‐2PACz suppresses the electron trapping, enhances the holes extraction, reduces the non‐radiative interfacial recombination, and improves the band alignment. Due to this superior interfacial charge‐carrier dynamics, NiOx:Cu+SAM is found to be the most suitable HTL for the monolithic CIGSe‐perovskite tandem devices, enabling a power‐conversion efficiency (PCE) of 23.4%, Voc of 1.72V, and a fill factor (FF) of 71%, while the remaining four HTLs suffer from prominent Voc and FF losses.
Monolithic Cu(In,Ga)Se2 (CIGSe)‐perovskite tandem solar cells (23.4%‐efficient) manufactured on CIGSe absorbers with a non‐negligible surface roughness is demonstrated. Conformal coverage of the bottom sub‐cell, shunt prevention and high effective lifetime in the top cell, and fast hole extraction, favorable band alignment, and suppressed electron trapping at the HTL‐perovskite interface are achieved by using copper‐doped nickel oxide NiOx:Cu + 2‐(3,‐6Dimethoxy‐9H‐carbazol‐9yl)ethylphosphonic acid (MeO‐2PACz) as a hole‐transporting bi‐layer.
Outstanding optoelectronic properties of mixed tin‐lead perovskites are the cornerstone for the development of high‐efficiency all‐perovskite tandems. However, recombination losses in Sn‐Pb ...perovskites still limit the performance of these perovskites, necessitating more fundamental research. Here, rubidium iodide is employed as an additive for methylammonium‐free Sn‐Pb perovskites. It is first investigated the effect of the RbI additive on the perovskite composition, crystal structure, and element distribution. Quasi‐Fermi level splitting and transient photoluminescence measurements reveal that the RbI additive reduces recombination losses and increases carrier lifetime of the perovskite films. This finding is attributed to an approximately ten‐fold reduction in the defect density following RbI treatment, as probed using constant final state yield photoelectron spectroscopy. Additionally, the concentration of Sn vacancies is also reduced, and the perovskite film becomes less p‐type both in the bulk and at the interface towards the electron contact. Thus, the conductivity for electrons increases, improving carrier extraction. As a result, the open‐circuit voltage of RbI‐containing solar cells improves by 61 mV on average, with the best efficiency >20%. This comprehensive study demonstrates that RbI is effective at reducing recombination losses and carrier trapping, paving way for a new approach to Sn‐Pb perovskite solar cell research.
Rubidium iodide as an additive improves properties of methylammonium‐free tin‐lead perovskite films, including larger grain size. It further reduces nonradiative recombination losses, increases carrier lifetime, reduces defect densities, and suppresses Sn (IV) vacancy formation. Therefore, the open‐circuit voltage of RbI‐containing tin‐lead perovskite solar cells increases by 61 mV on average with best power conversion efficiencies of up to 20.12%.
The next technological step in the exploration of metal‐halide perovskite solar cells is the demonstration of larger‐area device prototypes under outdoor operating conditions. The authors here ...demonstrate that when slot‐die coating the halide perovskite layers on large areas, ribbing effects may occur but can be prevented by adjusting the precursor ink's rheological properties. For formamidinium lead triiodide (FAPbI3) precursor inks based on 2‐methoxyethanol, the ink viscosity is adjusted by adding acetonitrile (ACN) as a co‐solvent leading to smooth FAPbI3 thin‐films with high quality and layer homogeneity. For an optimized content of 46 vol% of the ACN co‐solvent, a certified steady‐state performance of 22.3% is achieved in p‐i‐n FAPbI3‐perovskite solar cells. Scaling devices to larger areas by making laser series‐interconnected mini‐modules of 12.7 cm2, a power conversion efficiency of 17.1% is demonstrated. A full year of outdoor stability testing with continuous maximum power point tracking on encapsulated devices is performed and it is demonstrated that these devices maintain close to 100% of their initial performance during winter and spring followed by a significant performance decline during warmer summer months. This work highlights the importance of the real‐condition evaluation of larger area device prototypes to validate the technological potential of halide perovskite photovoltaics.
With the introduction of a low‐viscosity solvent (acetonitrile), the ribbing effect in slot‐die coated films is reduced and the morphology of films improved. A certified perovskite solar cell with steady state power conversion efficiency of 22.35% is achieved by slot die coating. Finally, the encapsulated devices are subjected to outdoor conditions for a one‐year stability test.
Radiation‐resistant but cost‐efficient, flexible, and ultralight solar sheets with high specific power (W g−1) are the “holy grail” of the new space revolution, powering private space exploration, ...low‐cost missions, and future habitats on Moon and Mars. Herein, this study investigates an all‐perovskite tandem photovoltaic (PV) technology that uses an ultrathin active layer (1.56 µm) but offers high power conversion efficiency, and discusses its potential for high‐specific‐power applications. This study demonstrates that all‐perovskite tandems possess a high tolerance to the harsh radiation environment in space. The tests under 68 MeV proton irradiation show negligible degradation (<6%) at a dose of 1013 p+ cm−2 where even commercially available radiation‐hardened space PV degrade >22%. Using high spatial resolution photoluminescence (PL) microscopy, it is revealed that defect clusters in GaAs are responsible for the degradation of current space‐PV. By contrast, negligible reduction in PL of the individual perovskite subcells even after the highest dose studied is observed. Studying the intensity‐dependent PL of bare low‐gap and high‐gap perovskite absorbers, it is shown that the VOC, fill factor, and efficiency potentials remain identically high after irradiation. Radiation damage of all‐perovskite tandems thus has a fundamentally different origin to traditional space PV.
Efficient all‐perovskite‐based tandem photovoltaics (PV) are shown to be radiation hard, surpassing state‐of‐the‐art industry‐standard space PV. Combining high specific power with good resilience to the harsh radiation environment in space, they promise a next‐generation of lightweight and cost‐efficient solutions to power private space exploration, low‐cost missions as well as future habitats on the Moon and Mars.
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