Mark Khenkin

• PhD
• PostDoc Position at Helmholtz-Zentrum Berlin für Materialien und Energie

Photoluminescence (PL) spectroscopy is a valuable tool fordegradation studies of perovskite‐based photovoltaic materials. The wavelength‐sensitive nature of the photo‐induced processes implies a preference for sunlight as the photo‐excitation source for such PL studies. This study reports on the design and experimental validation of a new setup for...

Perovskite solar cells (PSCs) are expected to transform the photovoltaic market; however, their unproven operational stability requires urgent attention, particularly accelerated aging tests. Currently, illumination is the primary stressor in such tests. In this work, we present an accelerated aging procedure consisting of prolonged forward biasing...

Encapsulation is a critical topic to ensure the successful implementation of perovskite photovoltaics. Recently, vacuum lamination has been shown as a promising approach that combines compatibility with current industrial processes in conventional photovoltaic (PV) manufacturing and suitability to achieve good results with perovskites. Here, we exp...

The stability of perovskite‐based tandem solar cells (TSCs) is the last major scientific/technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si/perovskite and...

For the commercialization of perovskite solar cells (PSCs), detection of associated degradation mechanisms and mitigation of their effect is of paramount importance. The former requires outdoor and indoor stability tests to detect these mechanisms under real operation conditions and to accelerate them under controlled environments. Herein, the ther...

Perovskite solar cells have shown a strong increase in efficiency over the last 15 years. With a record power conversion efficiency on small area above 34%, perovskite/silicon tandem solar cells already exceed the efficiency limit of silicon solar cells and their efficiency is expected to increase further. While predicted to take large markets shar...

Perovskite‐based solar cells exhibit peculiar outdoor performance which is not yet fully understood. The results of outdoor tests may contain hidden, but valuable information that cannot be fully extracted from measurements alone. One such phenomenon is the effect of nighttime degradation and the subsequent light‐soaking recovery, which can take fr...

Halide perovskite is a material that shows great promise in producing renewable energy. It offers one of the most efficient forms of photovoltaics for large-scale production. However, while perovskite solar cell devices are more efficient than many established technologies, their long-term stability outdoors is still being determined. Most studies...

While perovskite solar cells have reached competitive efficiency values during the last decade, stability issues remain a critical challenge to be addressed for pushing this technology towards commercialisation. In this study, we analyse a large homogeneous dataset of Maximum Power Point Tracking (MPPT) operational ageing data that we collected wit...

When PV is installed in the field, the module technologies are rated according to their output energy yield under local operating conditions rather than at standard test conditions (STC), where the spectrum is set to AM1.5G. Care must be taken as this standard is not optimal for all latitudes and the solar spectral distribution variations are one p...

Perovskite solar cells represent one of the most promising emerging photovoltaic technologies due to their high power conversion efficiency. However, despite of the huge progress made not only in terms of the efficiency achieved, but also fundamental understanding of relevant physics of the devices and issues which affect their efficiency and stabi...

This article provides datasets containing three years worth of solar spectra for the optimum installation angle of 35° and the building-integrated-photovoltaics relevant vertical angle of 90°. These datasets were obtained by measuring the spectrally resolved solar spectra using a five minute interval, where two sets of spectrometers, which measure...

Perovskite solar cells are the most dynamic emerging photovoltaic technology and attracts the attention of thousands of researchers worldwide. Recently, many of them are targeting device stability issues–the key challenge for this technology–which has resulted in the accumulation of a significant amount of data. The best example is the “Perovskite...

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...

Forecasting the real-world stability of perovskite solar cells (PSCs) using indoor accelerated tests is a significant challenge on the way to commercialising this highly anticipated PV technology. The lack of...

Operational stability keeps perovskite photovoltaics from being massively introduced in the energy market. Stability assessment studies can last for months or even years. Concentrated solar light to accelerate degradation of perovskite thin films (PTF) [1] and solar cells (PSC) [2] has already been demonstrated. Photoluminescence (PL) can be the mo...

Perovskite solar cells (PSCs) have shown great potential for next-generation photovoltaics. One of the main barriers to their commercial use is their poor long-term stability under ambient conditions and, in particular, their sensitivity to moisture and oxygen. Therefore, several encapsulation strategies are being developed in an attempt to improve...

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 sola...

Over the past decade, perovskite solar cells have travelled an amazing way towards high efficiency. However, a major roadblock remaining is the operational stability, while achieving technological maturity and proving real-world stability is crucial to gain trust among investors. In that sense, it is of high interest to be able to predict the opera...

Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep u...

The research on halide perovskites is in its peak activity at the moment due to the material's potential application in photovoltaics. It is well known that slow processes, from seconds to minutes, are very significant in perovskite films and devices as compared to conventional photovoltaic materials. The kinetics of photo-luminescence (PL) is info...

Degradation rates in perovskite solar cells (PSC) were previously shown to be bias‐dependent, however little is known about the mechanisms and driving factors that account for such degradation. Herein we demonstrate that stability study under concentrated sunlight is a powerful experimental methodology to investigate bias‐dependent PSC degradation...

Initial stages of photo‐degradation of CH3NH3PbI3 (MAPbI3) thin films prior to any significant change in light absorption are studied in experiments with independent control of sample temperature and intensity of concentrated sunlight from 50 to 500 suns. Photo‐stability of the MAPbI3 film is revealed to be extremely sensitive to the sample tempera...

We report on utilizing free-standing hybrid perylenediimide/carbon nanotube (PDI /CNT) films fabricated in air as back contacts for fully inorganic perovskite solar cells (Glass/FTO/dense TiO2/mesoporous TiO2/CsPbBr3/back electrode). The back contact electrode connection is performed by film transfer rather than by vacuum deposition or by wet proce...

Understanding device instability mechanisms in halide perovskite solar cells (PSCs) is the key aspect to achieve a breakthrough in photovoltaics. One of the puzzling questions in this regard is electrical bias-dependent degradation of PSCs. Several mechanisms have been suggested to explain the effect, but none are sufficient to embrace all observat...

Photo-luminescence (PL) of the perovskite is a sensitive optical property directly linked to the performance of solar cells. Although it has been traditionally used to probe and monitor carrier recombination under laser excitation, photovoltaic operation intuitively implies the sun for photo-excitation. For this reason, we have developed a new conf...

The development of hybrid organic-inorganic halide perovskite solar cells (PSCs) that combine high performance and operational stability is vital for implementing this technology. Recently, reversible improvement and degradation of PSC efficiency have been reported under illumination-darkness cycling. Quantifying the performance and stability of ce...

The operational stability of perovskite solar cells (PSCs) remains one of the limiting factors of their commercial implementation. We studied the long-term outdoor stability, as well as the dynamics of the cells' degradation, under constant, simulated sunlight indoor and their recovery in the dark, of ITO/SnO2/ Cs0.05((CH3NH3)0.15(CH(NH2)2)0.85)0.9...

Two types of independent anisotropic structures have been formed simultaneously in amorphous hydrogenated films by applying a femtosecond laser pulse to them, i.e., a structure with a period of several micrometers to several tens of micrometers and a structure with a period of several hundred nanometers. The formation mechanisms of these strictures...

Halide perovskites are widely studied due to their potential applications in solar cells. Despite the remarkable success in increasing perovskite solar cell efficiency, the underlying photophysical processes remain unclear. To cover this gap, we studied temperature,spectral, and light intensity dependence of photoconductivity of CH3NH3PbI3 films in...

In this work, we present new results on the plasma processing and structure of hydrogenated polymorphous silicon (pm-Si:H) thin films. pm-Si:H thin films consist of a low volume fraction of silicon nanocrystals embedded in a silicon matrix with medium range order, and they possess this morphology as a significant contribution to their growth comes...

The optical and photoelectric properties of present-day photosensitive polymers are of particular interest due to their prospects for use in various photoelectric applications. Here the absorption edge is studied by the constant photocurrent method which is widely used for studies of inorganic materials. For the objects to be studied, PCDTBT and PT...

Crystallization of amorphous hydrogenated silicon films with femtosecond laser pulses is one of the promising ways to produce nanocrystalline silicon for photovoltaics. The structure of laser treated films is the most important factor determining materials' electric and photoelectric properties. In this work we investigated the effect of femtosecon...

We have studied structural, electrical and photoluminescence properties of hydrogenated nanocrystalline silicon films with different crystalline volume fractions (from 0—pristine amorphous silicon—to 55%). The crystalline volume fraction and the average diameter of Si nanocrystals were estimated using the position and the intensity of the peaks in...

Ultrafast laser processing of semiconductors is a rapidly developing field of material science at the moment. In particular, femtosecond laser crystallization of amorphous hydrogenated silicon thin films has a big potential in photovoltaics. However laser treatment causes dehydrogenation process which decreases materials' photosensitivity and thus...

Optical and photoelectric properties of modern photosensitive polymers are of great interest due to their prospects for photovoltaic applications. In particular, an investigation of absorption and photoconductivity edge of these materials could provide valuable information. For these purpose we applied the constant photocurrent method which has pro...

Amorphous and microcrystalline hydrogenated silicon is an important material in modern thinfilm electronics. In some cases, the electrical parameters of silicon film samples depend on the ambient environment, in particular, the air. In this work we studied the effect of air exposure on the electrical properties of two-phase silicon films with a vol...

We demonstrate femto- and picosecond laser assisted nanostructuring of hydrogenated amorphous silicon (a-Si:H). The laser-induced periodic sub-wavelength structures exhibit the dichroism and giant form birefringence giving extra dimensions to the polarization sensitive image recording.

A femto- and picosecond laser assisted periodic nanostructuring of hydrogenated amorphous silicon (a-Si:H) is demonstrated. The grating structure with the subwavelength modulation of refractive index shows form birefringence (Δn ≈ −0.6) which is two orders of magnitude higher than commonly observed in uniaxial crystals and femtosecond laser nanostr...

Femtosecond laser processing of hydrogenated amorphous silicon is a perspective method for thin film solar cells production. It allows to make local crystallization and surface texturing of the films which results in the enhancement of their light absorption and stability of parameters. Thickness of modified material depends strongly on a laser wav...

Conventional optics (e.g. lenses or mirrors) manipulates the phase via optical path difference by controlling thickness or refractive index of material. Recently, a promising type of optics emerged which exploits geometric phase shift, when a lightwave is transformed by parameter other than optical path difference, e.g. polarization. Here, wavefron...

Spectral dependences of photoconductivity in thin layers of polyconjugated polymers (PCDTBT, PTB7) and their composites with a fullerene derivative (PC70BM), which are promising for the development of organic solar cells, have been studied. It was found that the photoconductivity in the polymeric composite exceeds that in the polymer in the whole s...

The crystallization of hydrogenated amorphous silicon films with femtosecond laser pulses is one of the promising ways to produce nanocrystalline silicon for photovoltaics. The structure of laser treated films and their hydrogen content are the most important factors for determining the photoelectric properties of materials. In this work we investi...

Thin film technology based on hydrogenated amorphous silicon (a-Si:H) has been playing a significant role in thin-film photovoltaics. However, a-Si:H based solar cells suffer from a low carrier mobility and light-induced degradation. In order to diminish these effects, tandem solar cells based on amorphous and nanocrystalline silicon (nc-Si) are de...

Crystallization of amorphous hydrogenated silicon thin films with femtosecond laser pulses is a currently developable technique for nanocrystalline silicon production for optoelectronics applications. The significant drawback of this technology is the hydrogen losses upon laser treatment of the film, while certain hydrogen concentration is essentia...

Femtosecond laser assisted crystallization is used to produce nanocrystalline silicon from hydrogenated amorphous silicon. Changes in structural, optical, electrical and photoelectric properties of laser modified amorphous silicon were investigated. Laser treated films were characterized using atomic force microscopy, Raman spectroscopy, constant p...

We have studied the Raman spectra of initially amorphous hydrogenated silicon (a-Si:H) films upon their exposure to femtosecond laser-radiation pulses with the fluence varied within 30–155 mJ/cm2. The distribution of the volume fraction of a crystalline phase over the surface of processed films is determined for the first time and a correlation is...

The structural, optical, and photoelectric properties of polymorphous silicon films produced by plasma-enhanced chemical vapor deposition from a mixture of monosilane and hydrogen at high pressure are studied. Variations in the pressure of the gas mixture used for film production barely change the Raman spectra of the films, but induce changes in t...

The structural and electronic properties of thin hydrogenated polymorphous silicon films obtained by plasma-enhanced chemical vapor deposition from hydrogen (H2) and monosilane (SiH4) gas mixture have been studied by means of transmission electron microscopy, electron paramagnetic resonance (EPR) spectroscopy, and Raman spectroscopy. It has been es...

We have studied structural, electrical, photoelectric and optical properties of two series of polymorphous silicon thin films deposited by PECVD with variation of silane and hydrogen gas mixture pressure and substrate temperature. The change of gas pressure did not affect substantially films' Raman spectra, but resulted in changes of photoconductiv...

Исследованы спектральные зависимости коэффициента поглощения в тонких пленках аморфного гидрированного кремния, полученных разложением смеси моносилана и водорода при относительной доле водорода в газовой смеси, соответствующей условиям начала формирования нанокристаллической фазы в структуре пленок. Для измерения спектральных зависимостей коэффици...

Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabri...

The effect of the femtosecond laser treatment of hydrogenated amorphous silicon (a-Si:H) films on their structural, optical, and photoelectric properties is studied. Under the experimental conditions applied in the study, laser treatment of the film with different radiation intensities induces structural changes that are nonuniform over the film su...

This paper studies the effect of femtosecond laser treatment in air of hydrogenated amorphous silicon thin films (a-Si:H) on their structural, electrical and photoelectric properties. The possibility of laser-induced crystallization of a-Si:H films with controlled crystalline volume fraction was shown. A sufficient increase of dark conductivity was...

Photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from a monosilane-hydrogen mixture have been studied at a fraction of hydrogen in the mixture that corresponds to the onset of formation of a nanocrystalline phase in the structure of the films obtained. A behavior untypical of amorpho...