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Nanostructured tin oxide (SnO2) is a very promising electron transport layer (ETL) for perovskite solar cells (PSCs) that allows low-temperature processing in the planar n–i–p architecture. However, minimizing current–voltage (J–V) hysteresis and optimizing charge extraction for PSCs in this architecture remains a challenge. In response to this, we study and optimize different types of single- and bilayer SnO2 ETLs. Detailed characterization of the optoelectronic properties reveals that a bilayer ETL composed of lithium (Li)-doped compact SnO2 (c(Li)-SnO2) at the bottom and potassium-capped SnO2 nanoparticle layers (NP-SnO2) at the top enhances the electron extraction and charge transport properties of PSCs and reduces the degree of ion migration. This results in an improved PCE and a strongly reduced J–V hysteresis for PSCs with a bilayer c(Li)-NP-SnO2 ETL as compared to reference PSCs with a single-layer or undoped bilayer ETL. The champion PSC with c(Li)-NP-SnO2 ETL shows a high stabilized PCE of up to 18.5% compared to 15.7%, 12.5% and 16.3% for PSCs with c-SnO2, c(Li)-SnO2 and c-NP-SnO2 as ETL, respectively.

Perovskite solar cells (PSCs) are among the most promising emerging photovoltaic technologies, demonstrating power conversion efficiencies (PCEs) close to 24%. The major challenge hampering commercialization of this technology is the low stability toward inevitable stress factors of PV modules such as temperature variations. Temperature variations are reported to induce a decline in photocurrent of up to 80%, depending on the device architecture, the charge transport layers, and the perovskite absorber material. The effect is particularly pronounced in methylammonium lead iodide-based PSCs, with TiO2 as the electron transport layer (ETL) and spiro-MeOTAD as the hole transport layer (HTL). This article reports on three different strategies to overcome the temperature-variation-induced degradation by altering the interfaces. The charge selective transport layers, the perovskite absorber layer composition, and the perovskite deposition technique are varied. We find that the interface between the ETL and the perovskite layer is the key to temperature-variation-induced degradation. We demonstrate stable PSCs with regard to temperature variations with PCEs as high as 19.5%. Finally, the relevance of the temperature-variation-induced degradation for outdoor applications is shown by stressing PSCs with real outdoor temperature profiles (between 21 and 75 °C).

Defect states are known to trigger trap-assisted nonradiative recombination, restricting the performance of perovskite solar cells (PSCs). Here, we investigate the trap states in long-term thermally stressed methylammonium lead iodide (MAPbI

Hybrid lead halide perovskite solar cells (PSCs) in tandem application with copper indium gallium diselenide (CIGS) solar cells represent one of the most promising all-thin-film technologies for ne...

Vacuum-based deposition techniques are a common route for the fabrication of high-quality optoelectronic devices on an industrialized scale at low cost and high yield. In the field of perovskite-based photovoltaics, however, vacuum deposition methods are less researched in the community today. Even though the fundamental concept of thermal evaporation of perovskite-based solar cells has been demonstrated, the number of reports about efficient upscalable all-evaporated approaches employing inexpensive raw materials is still limited. In this contribution, a novel architecture for efficient all-evaporated perovskite solar cells in pin -architecture based on a co-evaporated CH3NH3PbI3 absorber deposited on top of an electron-beam evaporated NiOx hole transport layer is reported. Stabilized power conversion efficiencies as high as 16.1% are achieved, resulting in the most efficient thermally evaporated perovskite solar cells employing a pin -architecture. Moreover, it is the first time in the literature that a co-evaporated perovskite absorber deposited directly on top of a metal oxide exceeeds a stable power conversion efficiency above 15%. Next to efficient devices, a remarkable stability against temperature variations up to 80 °C is demonstrated, highlighting the promising thermal stability of the employed charge extracting layers. Replacing the expensive gold rear electrode by copper reduces the material costs of the approach significantly while maintaining a good device performance and stability. The homogeneity and ease of upscaling of the all-evaporated approach toward industrial relevant areas is demonstrated by light-beam induced current mapping. Finally, a homogeneous deposition of the functional layers of the approach on top of a textured silicon wafer is shown.

One of the great challenges of hybrid organic–inorganic perovskite photovoltaics is the material’s stability at elevated temperatures. Over the past years, significant progress has been achieved in the field by compositional engineering of perovskite semiconductors, e.g., using multiple-cation perovskites. However, given the large variety of device architectures and nonstandardized measurement protocols, a conclusive comparison of the intrinsic thermal stability of different perovskite compositions is missing. In this work, we systematically investigate the role of cation composition on the thermal stability of perovskite thin films. The cations in focus of this study are methylammonium (MA), formamidinium (FA), cesium, and the most common mixtures thereof. We compare the thermal degradation of these perovskite thin films in terms of decomposition, optical losses, and optoelectronic changes when stressed at 85 °C for a prolonged time. Finally, we demonstrate the effect of thermal stress on perovskite thin films with respect to their performance in solar cells. We show that all investigated perovskite thin films show signs of degradation under thermal stress, though the decomposition is more pronounced in methylammonium-based perovskite thin films, whereas the stoichiometry in methylammonium-free formamidinium lead iodide (FAPbI₃) and formamidinium cesium lead iodide (FACsPbI₃) thin films is much more stable. We identify compositions of formamidinium and cesium to result in the most stable perovskite compositions with respect to thermal stress, demonstrating remarkable stability with no decline in power conversion efficiency when stressed at 85 °C for 1000 h. Thereby, our study contributes to the ongoing quest of identifying the most stable perovskite compositions for commercial application.

Vacuum-based deposition of optoelectronic thin films has a long-standing history. However, in the field of perovskite-based photovoltaics, these techniques are still not as advanced as their solution-based counterparts. Although high-efficiency vacuum-based perovskite solar cells reaching power conversion efficiencies (PCEs) above 20% are reported, the number of studies on the underlying physical and chemical mechanism of the co-evaporation of lead iodide and methylammonium iodide is low. In this study, the impact of one of the most crucial process parameters in vacuum processes���the substrate material���is studied. It is shown that not only the morphology of the co-evaporated perovskite thin films is significantly influenced by the surface polarity of the substrate material, but also the incorporation of the organic compound into the perovskite framework. Based on these studies, a selection guide for suitable substrate materials for efficient co-evaporated perovskite thin films is derived. This selection guide points out that the organic vacuum-processable hole transport material 2,2���,7,7���-tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene is an ideal candidate for the fabrication of efficient all-evaporated perovskite solar cells, demonstrating PCEs above 19%. Furthermore, building on the insights into the formation of the perovskite thin films on different substrate materials, a basic crystallization model for co-evaporated perovskite thin films is suggested.

Wide-bandgap the organo-metal halide perovskite solar cells (PSCs) are key for high performance perovskite-based tandem photovoltaics. One key aspect limiting the overall power conversion efficiency (PCE) in the 4-terminal tandem architecture is the imperfect transmission of the incident light below the bandgap of top PSCs. Here, we present periodic and disordered nanostructured ITO electrodes as new strategies to reduce reflection losses and transmission of PSCs. Using the nanostructured ITO, the short-circuit current-density is improved compared to planar references and as a result, an increase in the overall PCE of the solar cells is achieved.

Reducing non-radiative recombination losses by advanced passivation strategies is pivotal to maximize the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Previously, polymers such as poly(methyl methacrylate), poly(ethylene oxide), and polystyrene were successfully applied in solution-processed passivation layers. However, controlling the thickness and homogeneity of these ultra-thin passivation layers on top of polycrystalline perovskite thin films is a major challenge. In response to this challenge, this work reports on chemical vapor deposition (CVD) polymerization of poly(p-xylylene) (PPX) layers at controlled substrate temperatures (14–16 °C) for efficient surface passivation of perovskite thin films. Prototype double-cation PSCs using a ∼1 nm PPX passivation layer exhibit an increase in open-circuit voltage (V$_{OC}$) of ∼40 mV along with an enhanced fill factor (FF) compared to a non-passivated PSC. These improvements result in a substantially enhanced PCE of 20.4% compared to 19.4% for the non-passivated PSC. Moreover, the power output measurements over 30 days under ambient atmosphere (relative humidity ∼40–50%) confirm that the passivated PSCs are more resilient towards humidity-induced degradation. Considering the urge to develop reliable, scalable and homogeneous deposition techniques for future large-area perovskite solar modules, this work establishes CVD polymerization as a novel approach for the passivation of perovskite thin films.

The rise in the power conversion efficiency (PCE) of perovskite solar cells has triggered enormous interest in perovskite-based tandem photovoltaics. One key challenge is to achieve high transmission of low energy photons into the bottom cell. Here, nanostructured front electrodes for 4-terminal perovskite/crystalline-silicon (perovskite/c-Si) tandem solar cells are developed by conformal deposition of indium tin oxide (ITO) on self-assembled polystyrene nanopillars. The nanostructured ITO is optimized for reduced reflection and increased transmission with a tradeoff in increased sheet resistance. In the optimum case, the nanostructured ITO electrodes enhance the transmittance by ∼7% (relative) compared to planar references. Perovskite/c-Si tandem devices with nanostructured ITO exhibit enhanced short-circuit current density (2.9 mA/cm2 absolute) and PCE (1.7% absolute) in the bottom c-Si solar cell compared to the reference. The improved light in-coupling is more pronounced for elevated angle of incidence. Energy yield enhancement up to ∼10% (relative) is achieved for perovskite/c-Si tandem architecture with the nanostructured ITO electrodes. It is also shown that these nanostructured ITO electrodes are also compatible with various other perovskite-based tandem architectures and bear the potential to improve the PCE up to 27.0%.

High‐efficiency perovskite‐based solar cells can be fabricated via either solution‐processing or vacuum‐based thin‐film deposition. However, both approaches limit the choice of materials and the accessible device architectures, due to solvent incompatibilities or possible layer damage by vacuum techniques. To overcome these limitations, the lamination of two independently processed half‐stacks of the perovskite solar cell is presented in this work. By laminating the two half‐stacks at an elevated temperature (≈90 °C) and pressure (≈50 MPa), the polycrystalline perovskite thin‐film recrystallizes and the perovskite/charge transport layer (CTL) interface forms an intimate electrical contact. The laminated perovskite solar cells with tin oxide and nickel oxide as CTLs exhibit power conversion efficiencies of up to 14.6%. Moreover, they demonstrate long‐term and high‐temperature stability at temperatures of up to 80 °C. This freedom of design is expected to access both novel device architectures and pairs of CTLs that remain usually inaccessible.

In this work, passivation interlayers are investigated that enable high open-circuit voltage (V OC ) in wide-bandgap perovskite (WBP) solar cells. The interlayers are fabricated by processing a thin film of a large cation precursor on top of a 3D WBP thin-film (E G ~ 1.72 eV). The large cations n-butylammonium bromide (BABr) and ethylammonium bromide (EABr) show promising performance in WBP solar cells with stable power output conversion efficiencies of up to 19.4% and 17.9%, respectively. The corresponding V OC of these devices reaches values up to 1.31 V and 1.27 V for BABr and EABr, respectively. Compared to the reference devices without passivation interlayer (V OC ~ 1.23 V), this corresponds to an improvement in V OC of up to around 80 meV (BABr) and 40 meV (EABr), respectively. This enhancement in V OC originates from a reduction in non-radiative recombination losses. For the case of BABr, we reported already in a previous publication that a hybrid 2D/3D perovskite heterostructures is formed. Building on these results, in this proceeding paper we compare the performance of WBP solar cells using the large cation BABr and EABr for the processing of a passivation interlayers.

High power conversion efficiency (PCE) perovskite solar cells (PSCs) rely on optimal alignment of the energy bands between the perovskite absorber and the adjacent charge extraction layers. However, since most of the materials and devices of high performance are prepared by solution‐based techniques, a deposition of films with thicknesses of a few nanometers and therefore a detailed analysis of surface and interface properties remains difficult. To identify the respective photoactive interfaces, photoelectron spectroscopy measurements are performed on device stacks of methylammonium‐lead‐iodide (MAPI)‐based PSCs in classical and inverted architectures in the dark and under illumination at open‐circuit conditions. The analysis shows that vacuum‐deposited MAPI perovskite absorber layers are n‐type, independent of the architecture and of the charge transport layer that it is deposited on (n‐type SnO$_{2}$ or p‐type NiO$_{x}$). It is found that the majority of the photovoltage is formed at the n‐MAPI/p‐HEL (hole extraction layer) junction for both architectures, highlighting the importance of this interface for further improvement of the photovoltage and therefore also the PCE. Finally, an experimentally derived band diagram of the completed devices for the dark and the illuminated case is presented.

The power conversion efficiency (PCE) of lead-halide perovskite solar cells (PSCs) is reported to increase over a period of days after their fabrication while they are stored in the dark. The effects underlying this spontaneous enhancement thus far are not understood. This work investigates the phenomenon for a variety of multi-cation-halide PSCs with different perovskite compositions and architectures. The observations reveal that spontaneous enhancement is not restricted to specific charge transport layers or perovskite compositions. The highest PCE observed in this study is an enhanced stable PCE of 19% (increased by 4% absolute). An increased open-circuit voltage is the primary contributor to the improved efficiency. Using time-resolved photoluminescence measurements, the initially present low-energy states are identified which disappear over a storage period of a few days. Furthermore, trap states probed by the thermally stimulated current technique exist in pristine PSCs and strikingly decrease for stored devices. In addition, the ideality factor approaches unity and X-ray diffraction analyses show lattice strain relaxation over the same period of time. These observations indicate that spontaneous enhancement of the PCE of PSCs is based on a reduction in trap-assisted non-radiative recombination possibly due to strain relaxation. Considering the demonstrated generality of spontaneous enhancement for different compositions of multi-cation-halide PSCs, our results highlight the importance of determining the absolute PCE increase initiated by spontaneous enhancement for developing high-efficiency PSCs.

Interlayers can strongly influence the interfaces of perovskite solar cells (PSCs), and significantly increase the cells’ stabilized power conversion efficiencies (PCEs). This study compares for the first time the fabrication of C60 interlayers, deposited either by solution-processing or vacuum-based thermal evaporation, at the interface between a SnO2 electron transport layer (ETL) and the perovskite (MAPbI3-xClx) absorber layer in a n-i-p architecture. We evaluate the influence of the C60 deposition method on the perovskite crystallization dynamics and relate it to the device performance. With an optimized C60 layer, the devices exhibit an improvement in the stabilized PCE along with reduced hysteresis. As a result, we achieve improvement from 12.5% to 17.3% on the stabilized PCE of the PSCs. Furthermore, we investigate the influence of the C60 layer thickness on the transport dynamics through time-resolved photoluminescence and transient absorption measurements. Finally, we demonstrate that the C60 interlayers stabilize the constant power output of the solar cells over time due to the reduction in charge carrier accumulation at the ETL/Perovskite interface. Our results indicate that the ETL/perovskite interface is a governing factor in the reduction of hysteresis and in the extension of the stability in the PSCs.

With demonstrated power conversion efficiencies close to 23%, perovskite-based photovoltaics is already able to compete with established technologies like silicon, CdTe and CIGS. However, next to high efficiencies, the potential low-cost fabrication of devices with sufficient stability under real-world conditions is of key importance for the future economic prospects of the perovskite technology. In this contribution, we report on a novel inexpensive architecture for efficient and highly reproducible, all-evaporated perovskite solar cells. Our evaporated CH3NH3PbI3 absorber is sandwiched between nickel oxide as hole transport material and C60 as electron transport material. By replacing the highly expensive hole transport layer Spiro-MeOTAD by electron-beam deposited nickel oxide and the gold back electrode by copper, we reduce the cost of materials on the lab-scale to one third of the price of the common stack based on Spiro-MeOTAD. At the same time, extraordinary stable devices even at operating temperatures of 80°C are achieved. Stabilized power conversion efficiencies under standard test conditions exceed values of 14%. Moreover, the vacuum deposition combines the ease of controlled deposition and a simple upscaling, making it a favorable process for industry. A homogenous and reproducible deposition on substrates with an area of up to 8x8 cm² is demonstrated by light beam induced current mapping, which is a fundamental requirement for the fabrication of larger prototype modules. Finally, as an inverted architecture with the anode deposited on top of the substrate the investigated layer stack is a promising candidate for two-terminal tandem devices on top of CIGS or p-type silicon.

Perovskite solar cells (PSCs) demonstrate excellent power conversion efficiencies (PCEs) but face severe stability challenges. One key degradation mechanism is exposure to ultraviolet (UV) light. However, the impact of different UV bands is not yet well established. Here, we systematically study the stability of PSCs on the basis of a methylammonium lead iodide (CH3NH3PbI3) absorber exposed to (i) 310–317 (UV-B range) and (ii) 360–380 nm (UV-A range), under accelerated conditions. We demonstrate that the investigated UV-B band is detrimental to the stability of PSCs, resulting in PCE degradation by more than 50% after an exposure period >1700 sun-hours. This finding is valid for architectures with a range of electron transport layers, including SnO2, compact-TiO2, electron-beam TiO2, and nanoparticle-TiO2. We also show that photodegradation is apparent for high, as well as for low illumination intensities of UV-B light, but not for illumination with UV-A wavelengths. Finally, we show that degradation of P...

Perovskite solar cells (PSCs) are one of the most promising emerging photovoltaic technologies, demonstrating high efficiencies and low fabrication costs. This work reports on the stability of high-efficient PSCs stressed with realistic temperature variations. The photocurrent is found to reversibly decline below 20% of the initial value in the most common device architecture based on a TiO 2 electron transport layer, upon cycling the temperature between 10°C and 60°C. In contrast, the photocurrent stabilizes for constant temperatures. The degradation can be prevented by replacing the electron transport layer with more stable materials. Finally, the impact of this degradation for outdoor application is shown by stressing PSCs with a real outdoor temperature profile.

This paper reports on the impact of outdoor temperature variations on the performance of organo metal halide perovskite solar cells (PSCs). It shows that the open-circuit voltage (VOC) of a PSC decreases linearly with increasing temperature. Interestingly, in contrast to these expected trends, the current density (JSC) of PSCs is found to decline strongly below 20% of the initial value upon cycling the temperatures from 10 to 60 °C and back. This decline in the current density is driven by an increasing series resistance and is caused by the fast temperature variations as it is not apparent for solar cells exposed to constant temperatures of the same range. The effect is fully reversible when the devices are kept illuminated at an open circuit for several hours. Given these observations, an explanation that ascribes the temperature variation-induced performance decline to ion accumulation at the contacts of the solar cell because of temperature variation-induced changes of the built-in field of the PSC is...

All-perovskite multijunction photovoltaics, combining a wide-bandgap (WBG) perovskite top solar cell (EG ≈1.6–1.8 eV) with a low-bandgap (LBG) perovskite bottom solar cell (EG 33%. While the research on WBG perovskite solar cells has advanced rapidly over the past decade, LBG perovskite solar cells lack PCE as well as stability. In this work, vacuum-assisted growth control (VAGC) of solution-processed LBG perovskite thin films based on mixed Sn–Pb perovskite compositions is reported. The reported perovskite thin films processed by VAGC exhibit large columnar crystals. Compared to the well-established processing of LBG perovskites via antisolvent deposition, the VAGC approach results in a significantly enhanced charge-carrier lifetime. The improved optoelectronic characteristics enable high-performance LBG perovskite solar cells (1.27 eV) with PCEs up to 18.2% as well as very efficient four-terminal all-perovskite tandem solar cells with PCEs up to 23%. Moreover, VAGC leads to promising reproducibility and potential in the fabrication of larger active-area solar cells up to 1 cm².

A key challenge for the commercialization of perovskite photovoltaics is the transfer of high‐quality spin coated perovskite thin‐films toward applying industry‐scale thin‐film deposition techniques, such as slot‐die coating, spray coating, screen printing, or inkjet printing. Due to the complexity of the formation of polycrystalline perovskite thin‐films from the precursor solution, efficient strategies for process transfer require advancing the understanding of the involved dynamic processes. This work investigates the fundamental interrelation between the drying dynamics of the precursor solution thin‐film and the quality of the blade coated polycrystalline perovskite thin‐films. Precisely defined drying conditions are established using a temperature‐stabilized drying channel purged with a laminar flow of dry air. The dedicated channel is equipped with laser reflectometry at multiple probing positions, allowing for in situ monitoring of the perovskite solution thin‐film thickness during the drying process. Based on the drying dynamics as measured at varying drying parameters, namely at varying temperature and laminar air flow velocity, a quantitative model on the drying of perovskite thin‐films is derived. This model enables process transfer to industry‐scale deposition systems beyond brute force optimization. Via this approach, homogeneous and pinhole‐free blade coated perovskite thin‐films are fabricated, demonstrating high power conversion efficiencies of up to 19.5% (17.3% stabilized) in perovskite solar cells.

Photoluminescence (PL) spectra of atomically thin 2D lead iodide perovskite films are shown to depend on excited-state density, especially at cryogenic temperatures. At high excited-state densities and low temperatures, free exciton (FE) emission is so suppressed by exciton-exciton annihilation (EEA) that other-normally much weaker-emissions dominate the PL spectrum, such as emission from bound excitons (BEs) or PbI, 2 inclusions. In the Ruddlesden-Popper perovskite with phenethylammonium (PEA) ligands (PEA, 2PbI, 4, PEPI), FE emission dominates at all temperatures at the excited-state densities reached with continuous wave excitation. At higher excited state densities reached with femtosecond pulsed excitation, the PL at temperatures under 100K is dominated by BE emission redshifted from that of FE by 40.3meV. Weak emission from PbI, 2 inclusions 170meV higher in energy than FE PL is also observable under these conditions. Equilibrium between BE and FE states explains why FE emission first increases with decreasing temperature from 290 until 140K and then decreases with decreasing temperature as the BEs become stable. A Dion-Jacobson (DJ) material based on 1,4-phenyl-enedimethanammonium (PDMA) supports the reduction of FE emission by EEA at cryogenic temperatures. However, in the PDMA-based DJ material, BE emission is never as pronounced. At low temperatures and high-excited state densities caused by pulsed excitation, a broad emission redshifted by 390meV from the FE dominates. Based on comparison with temperature-dependent measurements of PbI, 2 films, this emission is suggested to arise from PbI, 2 inclusions in the material. Possible avenues for improving PL at room temperature are discussed concerning these findings.