Hans Köbler

• Master of Science
• PhD Student at Helmholtz-Zentrum Berlin für Materialien und Energie

Perovskite solar cells (PSCs) are promising for high‐efficiency tandem applications, but their long‐term stability, particularly due to ion migration, remains a challenge. Despite progress in stabilizing PSCs, they still fall short compared to mature technologies like silicon. This study explores how different piperazinium salt treatments using iod...

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...

Developing efficient wide‐bandgap perovskites is critical to exploit the benefits of a multi‐absorber solar cell and engineering commercially attractive tandem solar cells. Here, a robust, additive‐free, methylammonium‐free triple halide composition for the fabrication of close‐to‐ideal wide‐bandgap perovskites (1.64 eV) is reported. The introducti...

Here, we report a detailed surface analysis of dry- and ambient air-annealed CsPbI3 filmsand their subsequent modified interfaces in perovskite solar cells. We revealed that annealing in ambientair does not adversely affect the optoelectronic properties of the semiconducting film; instead, ambientair-annealed samples undergo a surface modification,...

Nickel oxide (NiO 1+δ ) is a versatile material used in various fields such as optoelectronics, spintronics, electrochemistry, and catalysis which is prepared with a wide range of deposition methods. Herein, for the deposition of NiO 1+δ films, the reactive gas flow sputtering (GFS) process using a metallic Ni hollow cathode is developed. This tech...

The development of hole transport materials (HTMs) is a prolific area of research due to the application of these materials in various technologies such as organic light-emitting diodes (OLEDs) or perovskite solar cells (PSCs). HTMs have notably played a crucial role in the development of high-performance PSCs since in these devices, they not only...

In perovskite solar cells (PSCs) energy level alignment and charge extraction at the interfaces are the essential factors directly affecting the device performance. In this work, we present a modified interface between all-inorganic CsPbI3 perovskite and its hole-selective contact (spiro-OMeTAD), realized by the dipole molecule trioctylphosphine ox...

Inorganic metal halide perovskites such as CsPbI 3 are promising for high‐performance, reproducible and robust solar cells. However, inorganic perovskites are sensitive to humidity, which causes the transformation from the black phase to the yellow δ, non‐perovskite phase. Such phase instability has been a significant challenge to long‐term operati...

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...

In perovskite solar cells (PSCs) energy levels alignment and charge extraction at the interfaces are the essential factors directly affecting the device performance. In this work, we present a modified interface between all-inorganic CsPbI$_3$ perovskite and its hole selective contact (Spiro-OMeTAD), realized by a dipole molecule trioctylphosphine...

Improved stability and efficiency of two-terminal monolithic perovskite-silicon tandem solar cells will require reductions in recombination losses. By combining a triple-halide perovskite (1.68 electron volt bandgap) with a piperazinium iodide interfacial modification, we improved the band alignment, reduced nonradiative recombination losses, and e...

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...

Organic–inorganic hybrid halide perovskites are widely considered to be one the most promising material in photovoltaic technology, the use of this semiconductor as absorbent layer in solar cells has attracted considerable interest due to their excellent properties. It has been reported that the incorporation of potassium ion is a powerful strategy...

Metal halide perovskite solar cells may work for application in extreme temperatures, such as those experienced under extraterrestrial conditions. However, device performances in extreme temperatures are poorly investigated. This work systematically explores the performance of perovskite solar cells between −160 and 150 °C. In situ grazing‐incidenc...

Photostability is critical for long-term solar cell operation. While light-triggered defects are usually reported as evidence of material degradation, we reveal that the formation of certain defects in metal halide perovskites is crucial for protection against intense or prolonged light exposure. We identify an inherent self-regulating cycle of for...

In this research instrument article, the capabilities and details of a high‐throughput aging system for parallel maximum power point tracking (MPPT) of perovskite solar cells (PSCs), capable of assessing the operational stability of a large number of devices, are presented. The intention is to provide insights into the machine and the development p...

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...

Metal halide perovskites have attracted tremendous attention due to their excellent electronic properties. Recent advancements in device performance and stability of perovskite solar cells (PSCs) have been achieved with the application of self-assembled monolayers (SAMs), serving as stand-alone hole transport layers in the p-i-n architecture. Speci...

Interfaces play a crucial role in determining perovskite solar cells, (PSCs) performance and stability. It is therefore of great importance to constantly work toward improving their design. This study shows the advantages of using a hole‐transport material (HTM) that can anchor to the perovskite surface through halogen bonding (XB). A halo‐function...

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...

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 t...

Approaches to boost the efficiency and stability of perovskite solar cells often address one singular problem in a specific device configuration. In this work, we utilize a poly(ionic-liquid) (PIL) to...

Current perovskite solar cell efficiency is close to silicon's record values. Yet, the roadblock for industrialization of this technology is its stability. The stability of the solar cell not only depends on the stability of the perovskite material itself but also notably on its contact layers and their interface with the perovskite, which plays a...

Dendritic‐like hole transporting materials for perovskite solar cells have been prepared by functionalization of a clickable pillar[5]arene core with triarylamine dendrons. Importantly, the apparent structural complexity of the resulting compounds is not associated to a difficult synthesis which is a major advantage for applications in the field of...

“The preparation of novel hole transporting materials able to compete with the reference spiro‐OMeTAD, has been a hot topic in photovoltaics in the last years. In the present paper, we have proposed a new design principle for the preparation of hole transporting materials for perovskite solar cells. Our approach relies on the functionalization of a...

Multi‐branched molecules have recently demonstrated interesting behaviour as charge‐transporting materials within the fields of perovskite solar cells (PSCs). For this reason, extended triarylamine dendrons have been grafted onto a pillar[5]arene core to generate dendrimer‐like compounds, which have been used as hole‐transporting materials (HTMs) f...

Through the optimization of the perovskite precursor composition and interfaces to selective contacts, we achieved a p-i-n-type perovskite solar cell (PSC) with a 22.3% power conversion efficiency (PCE). This is a new performance record for a PSC with an absorber bandgap of 1.63 eV. We demonstrate that the high device performance originates from a...

Recent advancements in perovskite solar cell performance were achieved by stabilizing the α-phase of FAPbI3 in nip-type architectures. However, these advancements could not be directly translated to pin-type devices. Here, we fabricated a high-quality double cation perovskite (MA0.07FA0.93PbI3) with low bandgap energy (1.54 eV) using a two-step app...

Solar cells incorporating metal‐halide perovskite (MHP) semiconductors are continuing to break efficiency records for solution‐processed solar cell devices. Scaling MHP‐based devices to larger area prototypes requires the development and optimization of scalable process technology and ink formulations that enable reproducible coating results. It is...

For several years, scientists have been trying to understand the mechanisms that reduce the long‐term stability of perovskite solar cells. In this work, we examined the effect of water and photon flux on the stability of CH3NH3PbI3 perovskite films and solar cells using in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS), field...

The operation of halide perovskite optoelectronic devices, including solar cells and LEDs, is strongly influenced by the mobility of ions comprising the crystal structure. This peculiarity is particularly true when considering the long‐term stability of devices. A detailed understanding of the ion migration‐driven degradation pathways is critical t...

Inorganic perovskites with caesium (Cs⁺) as the cation have great potential as photovoltaic material if their phase purity and stability can be addressed. In this work, we studied a series of inorganic perovskites, and we found that the power conversion efficiency of solar cells with compositions CsPbI1.8Br1.2, CsPbI2.0Br1.0, and CsPbI2.2Br0.8 exhi...

Inorganic perovskites with cesium (Cs+) as the cation have great potential as photovoltaic materials if their phase purity and stability can be addressed. Herein, a series of inorganic perovskites is studied, and it is found that the power conversion efficiency of solar cells with compositions CsPbI1.8Br1.2, CsPbI2.0Br1.0, and CsPbI2.2Br0.8 exhibit...

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...

Halide perovskites are a strong candidate for the next generation of photovoltaics. Chemical doping of halide perovskites is an established strategy to prepare the highest efficient and the most stable perovskite-based solar cells. In this study, we unveil the doping mechanism of halide perovskites using the series of alkaline earth metals. We find...

Mixed cation/halide perovskites have led to a significant increase in the efficiency and stability of perovskite solar cells. However, mobile ionic defects inevitably exacerbate the photoinduced phase segregation and self‐decomposition of the crystal structure. Herein, ultrathin 2D nanosheets of oxo‐functionalized graphene/dodecylamine (oxo‐G/DA) a...