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Using advanced near UV photoemission spectroscopy PES in constant final state mode CFSYS with very high dynamic range, we investigate the triple cation lead halide perovskite Cs0.05 MA0.17FA0.83 0.95Pb I0.83Br0.17 3 and gain detailed insights into the density of occupied states DOS in the valence band and band gap. A valence band model is established which includes the parabolic valence band edge and an exponentially decaying band tail in a single equation. This allows to precisely determine two valence band maxima VBM at different k vectors in the angle integrated spectra, where the highest one, resulting from the VBM at the R point in the Brillouin zone, is found between 1.50 eV to 1.37 eV relative to the Fermi energy EF. We investigate quantitatively the formation of defect states in the band gap up to EF upon decomposition of the perovskites during sample transfer, storage, and measurements During near UV based PES, the density of defect states saturates at a value that is around four orders of magnitude below the density of states at the valence band edge. However, even short air exposure, or 3h of X ray illumination, increased their density by almost a factor of six and 40, respectively. Upon prolonged storage in vacuum, the formation of a distinct defect peak is observed. Thus, near UV CFSYS with modelling as shown here is demonstrated as a powerful tool to characterize the valence band and quantify defect states in lead halide perovskites

Light management strategies can increase the efficiency of perovskite single-junction and tandem solar cells. In this study, we present perovskite solar cells deposited on different shallow nanotex...

A quantitative analysis of the thermally induced degradation of various device relevant multi cation hybrid perovskite films is performed using spectroscopic ellipsometry, for temperatures between 80 and 120 C. The studied compositions are a triple cation perovskite Cs0.05 MA0.17FA0.83 0.95Pb Br0.17I0.83 3, a Rb containing variant Rb0.05Cs0.05 MA0.17FA0.83 0.90Pb Br0.17I0.83 3, and a methylammonium free Rb0.05Cs0.10FA0.85PbI3 composition. A very wide combined spectral range of 200 nm to 25 amp; 956;m is covered by combining the data from two separate instruments. The relative changes in organic cation concentrations are quantified from the middle infrared molecular absorption bands, leveraging the use of point by point fitting for increased sensitivity. Additionally, the formation of PbI2 and non perovskite amp; 948; CsPbI3 phases is evidenced from Bruggemann effective medium fits to the visible and ultraviolet complex refractive indices. Methylammonium is almost completely depleted from the relevant compositions within 100 to 285 min of thermal annealing. The MA free perovskite degrades faster at intermediate temperatures, which is attributed to phase instability due to the formation of amp; 948; CsPbI3 in addition to PbI2

This work focuses on 2D device simulation for perovskite/tandem solar cells, aiming to reproduce the experimental current-voltage curves and to explore further steps for efficiency improvements. The results demonstrate that a reasonable J-V curve can be obtained when the indium tin oxide (ITO) layer that interconnects both subcells is treated as either a semiconductor or conductor. In both cases, band to band tunneling and/or additional built-in voltage governed by proper work functions of ITO and tin oxide (SnOx) films are required to obtain the high experimental FFs of >80%. Optical and electrical losses in the tandem device are also addressed by quantum efficiencies (EQE, IQE) and reflectance simulation.

The power conversion efficiency (PCE) of perovskite/silicon tandem solar cells (PSTSCs) is expected to increase with optimized light management. In this work, we report on PSTSCs containing nanostructures enabling PCEs exceeding 26%. A hexagonal sinusoidal nanostructure with 750nm period was used. The structure was transferred into silicon by nanoimprint lithography and reactive ion etching. Perovskite top cells were deposited by spin-coating resulting in a full coverage of the nanostructure. PSTSC comprising these nanostructures yielded a steady-state PCE of 26.1% and a short-circuit current density of 19.5mA·cm−2.

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 synergy between 1 an improved perovskite absorber quality when introducing formamidinium chloride FACl as an additive in the triple cation Cs0.05FA0.79MA0.16PbBr0.51I2.49 Cs MAFA perovskite precursor ink, 2 an increased open circuit voltage, VOC, due to reduced recombination losses when using a lithium fluoride LiF interfacial buffer layer, and 3 high quality hole selective contacts with a self assembled monolayer SAM of [2 9H carbazol 9 yl ethyl]phosphonic acid 2PACz on ITO electrodes. While all devices exhibit a high performance after fabrication, as determined from current density voltage, J V, measurements, substantial differences in device performance become apparent when considering longer term stability data. A reduced long term stability of devices with the introduction of a LiF interlayer is compensated for by using FACl as an additive in the metal halide perovskite thin film deposition. Optimized devices maintained about 80 of the initial average PCE during maximum power point MPP tracking for gt;700 h. We scaled the optimized device architecture to larger areas and achieved fully laser patterned series interconnected mini modules with a PCE of 19.4 for a 2.2 cm2 active area. A robust device architecture and reproducible deposition methods are fundamental for high performance and stable large area single junction and tandem modules based on PSCs

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 amp; 948; 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

We present enhanced optical performance in perovskite/silicon tandem solar cells with smooth periodic nanotextures. Reflection losses in experimental devices are reduced by 1 mA/cm², enabling a power conversion efficiency >26%.

Summary Identification of electronic processes at buried interfaces of charge-selective contacts is crucial for photovoltaic and photocatalysis research. Here, transient surface photovoltage (SPV) is used to study the passivation of different hole-selective carbazole-based SAMs. It is shown that transient SPV and transient photoluminescence provide complementary information on charge transfer kinetics and trapping/de-trapping mechanisms, and that trap-assisted non-radiative recombination losses originate from electron trapping at the SAM-modified ITO/perovskite interface. The hole transfer rates and the density of interface electron traps, obtained by fitting SPV transients with a minimalistic kinetic model, depended strongly on the SAM's chemical structure, and densities of interface traps as low as 109 cm−2, on par with highly passivated c-Si surfaces, were reached for Me-4PACz, previously used in record perovskite/silicon tandem solar cells. The extracted hole transfer rate constants and interface trap densities correlated well with the corresponding fill factors and open-circuit voltages of high-efficiency solar cells.

Multi-junction solar cells provide an avenue to overcome fundamental efficiency limits of single-junction devices. The facile bandgap tunability of metal-halide perovskite solar cells renders them attractive building blocks for multi-junction architectures. Combinations with crystalline silicon and copper indium gallium selenide (CIGS) cells have been reported. All-perovskite tandem cells have likewise shown promising results. Meanwhile, narrow-gap non-fullerene acceptors (NFA) have revived the area of organic solar cells (OSCs) and unlocked skyrocketing efficiencies. Organic and perovskite semiconductors share similar processing technologies, which renders them attractive partners in multi junction architectures. As of yet, perovskite/organic tandem cells show subpar efficiencies of 20 per cent, limited by the low open circuit voltage (Voc) of wide-gap perovskite cells and losses introduced by the interconnect between the sub-cells. Here, we demonstrate two-terminal p-i-n perovskite/organic tandem cells with an efficiency of 23.5 per cent and a high Voc of 2.15 volts, operating near the levels predicted by a semi-empirical model. The perovskite sub-cells with optimized charge extraction layers afford an unsurpassed combination of a high Voc and fill-factor. The organic back-cells provide a high external quantum efficiency in the near-infrared. In surprising contrast to paradigmatic concerns about limited photostability of non-fullerene cells, we evidence an outstanding operational stability if excitons are predominantly generated on the NFA, which is the case in a tandem cell, where the illumination is spectrally filtered by the perovskite cell. A novel interconnect based on an ultra-thin (1.5 nanometers) metal like indium oxide layer offers unprecedented low optical/electrical losses. This work sets a new milestone for perovskite/organic tandem devices, that outperform the best p-i-n perovskite single junctions and are at par with perovskite/CIGS and all-perovskite multi-junctions. Perovskite/organic tandem architectures bear a realistic potential to reach an efficiency above 31%.

We show a monolithic perovskite/CIGS tandem solar cell with a certified PCE of 24.2% and a high V OC of 1.77 V, enabled by reduction of interface recombination. Using optical simulations, we further optimize the structure of the cell and compare it to perovskite/silicon tandem solar cells. The yearly energy yield of the perovskite/CIGS tandem is only 6% lower than that of the perovskite/silicon tandem, showing great potential of the perovskite/CIGS technology.

Summary Monolithic [Cs0.05(MA0.17FA0.83)0.95]Pb(I0.83Br0.17)3/Cu(In,Ga)Se2 (perovskite/CIGS) tandem solar cells promise high performance and can be processed on flexible substrates, enabling cost-efficient and ultra-lightweight space photovoltaics with power-to-weight and power-to-cost ratios surpassing those of state-of-the-art III-V semiconductor-based multijunctions. However, to become a viable space technology, the full tandem stack must withstand the harsh radiation environments in space. Here, we design tailored operando and ex situ measurements to show that perovskite/CIGS cells retain over 85% of their initial efficiency even after 68 MeV proton irradiation at a dose of 2 × 1012 p+/cm2. We use photoluminescence microscopy to show that the local quasi-Fermi-level splitting of the perovskite top cell is unaffected. We identify that the efficiency losses arise primarily from increased recombination in the CIGS bottom cell and the nickel-oxide-based recombination contact. These results are corroborated by measurements of monolithic perovskite/silicon-heterojunction cells, which severely degrade to 1% of their initial efficiency due to radiation-induced recombination centers in silicon., Graphical Abstract, Highlights • Halide perovskite sub-cells exhibit strong proton irradiation resiliency • Novel operando characterization distinguishes degradation of individual sub-cells • Perovskite/CIGS tandem solar cells retain 85% of their initial efficiency after irradiation • Perovskite/SHJ tandem solar cells degrade to 1% of their initial efficiency after irradiation, Context & Scale Monolithic perovskite/silicon and perovskite/CIGS tandem solar cells could facilitate large-scale decarbonization of the power sector, provided their long-term stability is proven. In this work, we test the stability of both technologies under high-energy proton irradiation. While this mimics the radiation environment in space, our versatile operando and ex situ methodology is also suitable for studying the long-term stability of multijunction solar cells for terrestrial applications. We find that perovskite/silicon tandem solar cells are unsuitable for space, whereas perovskite/CIGS tandems are radiation-hard, promising cheap, flexible, and ultra-lightweight space photovoltaics. Both the growing demand for smaller, cheaper satellites and the privatization of space exploration are revolutionizing space economics, providing an ideal niche for the commercialization of this new technology until the levelized cost-of-electricity can compete with current terrestrial photovoltaics., We propose and test monolithic perovskite/CIGS tandem solar cells for readily stowable, ultra-lightweight space photovoltaics. We design operando and ex situ measurements to show that perovskite/CIGS tandem solar cells retain over 85% of their initial power-conversion efficiency after high-energy proton irradiation. While the perovskite sub-cell is unaffected after this bombardment, we identify increased non-radiative recombination in the CIGS bottom cell and nickel-oxide-based recombination layer. By contrast, monolithic perovskite/silicon-heterojunction cells degrade to 1% of their initial efficiency due to radiation-induced defects in silicon.

Perovskite based tandem solar cells can increase the power conversion efficiency PCE of conventional single junction photovoltaic devices. Here, we present monolithic perovskite CIGSe tandem solar cells with a perovskite top cell fabricated directly on an as grown, rough CIGSe bottom cell. To prevent potential shunting due to the rough CIGSe surface, a thin NiOx layer is conformally deposited via atomic layer deposition on the front contact of the CIGSe bottom cell. The performance is further improved by an additional layer of the polymer PTAA at the NiOx perovskite interface. This hole transport bilayer enables a 21.6 stabilized PCE of the tandem device at amp; 8764;0.8 cm2 active area. We use TEM EDX measurements to investigate the deposition uniformity and conformality of the NiOx and PTAA layers. By absolute photoluminescence measurements, the contribution of the individual subcells to the tandem VOC is determined, revealing that further fine tuning of the recombination layers might improve the tandem VOC. Finally, on the basis of the obtained results, we give guidelines to improve monolithic perovskite CIGSe tandems toward predicted PCE estimates above 30

Metal halide perovskites show great promise to enable highly efficient and low cost tandem solar cells when being combined with silicon. Here, we combine rear junction silicon heterojunction bottom cells with p-i-n perovskite top cells into highly efficient monolithic tandem solar cells with a certified power conversion efficiency (PCE) of 25.0%. Further improvements are reached by reducing the current mismatch of the certified device. The top contact and perovskite thickness optimization allowed increasing the J SC above 19.5 mA cm -2, enabling a remarkable tandem PCE of 26.0%, however with a slightly limited fill factor (FF). To test the dependency of the FF on the current mismatch between the sub-cells, the tandems' J-V curves are measured under various illumination spectra. Interestingly, the reduced J SC in unmatched conditions is partially compensated by an enhancement of the FF. This finding is confirmed by electrical simulations based on input parameters from reference single junction devices. The simulations reveal that especially the FF in the experiment is below the expected value and show that with improved design we could reach 29% PCE for our monolithic perovskite/silicon tandem device and 31% PCE if record perovskite and silicon cell single junctions could be combined in tandem solar cells.

Efficient light management in monolithic perovskite/silicon tandem solar cells is one of the prerequisites for achieving high power conversion efficiencies (PCEs). Textured silicon wafers can be utilized for light management, however, this is typically not compatible with perovskite solution processing. Here, we instead employ a textured light management (LM) foil on the front-side of a tandem solar cell processed on a wafer with a planar front-side and textured back-side. This way the PCE of monolithic, 2-terminal perovskite/silicon-heterojunction tandem solar cells is significantly improved from 23.4% to 25.5%. Furthermore, we validate an advanced numerical model for our fabricated device and use it to optically optimize a number of device designs with textures at different interfaces with respect to the PCE and energy yield. These simulations predict a slightly lower optimal bandgap of the perovskite top cell in a textured device as compared to a flat one and demonstrate strong interdependency between the bandgap and the texture position in the monolithic stack. We estimate the PCE potential for the best performing both-side textured device to be 32.5% for a perovskite bandgap of 1.66 eV. Furthermore, the results show that under perpendicular illumination conditions, for optimized designs, the LM foil on top of the cell performs only slightly better than a flat anti-reflective coating. However, under diffuse illumination, the benefits of the LM foil are much greater. Finally, we calculate the energy yield for the different device designs, based on true weather data for three different locations throughout the year, taking direct as well as diffuse illumination fully into account. The results further confirm the benefits of front-side texture, even more for BIPV applications. Overall, devices built on a both-side textured silicon wafer perform best. However, we show that devices with textured LM foils on the cell's front-side are a highly efficient alternative.

Funder: European Research Council; Id: http://dx.doi.org/10.13039/501100000781, Funder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266, Funder: European Union's Horizon 2020, 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 (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.

For methylammonium lead iodide perovskite solar cells prepared by co-evaporation, power conversion efficiencies of over 20% have been already demonstrated, however, so far, only in n-i-p configuration. Currently, the overall major challenges are the complex evaporation characteristics of organic precursors that strongly depend on the underlying charge selective contacts and the insufficient reproducibility of the co-evaporation process. To ensure a reliable co-evaporation process, it is important to identify the impact of different parameters in order to develop a more detailed understanding. In this work, we study the influence of the substrate temperature, underlying hole-transport layer (polymer PTAA versus self-assembling monolayer molecule MeO-2PACz), and perovskite precursor ratio on the morphology, composition, and performance of co-evaporated p-i-n perovskite solar cells. We first analyze the evaporation of pure precursor materials and show that the adhesion of methylammonium iodide (MAI) is significantly reduced with increased substrate temperature, while it remains almost unaffected for lead iodide (PbI

Efficiency from hole-selective contacts Perovskite/silicon tandem solar cells must stabilize a perovskite material with a wide bandgap and also maintain efficient charge carrier transport. Al-Ashouri et al. stabilized a perovskite with a 1.68–electron volt bandgap with a self-assembled monolayer that acted as an efficient hole-selective contact that minimizes nonradiative carrier recombination. In air without encapsulation, a tandem silicon cell retained 95% of its initial power conversion efficiency of 29% after 300 hours of operation. Science , this issue p. 1300

The development of the simple synthesis schemes of organic semiconductors can have an important contribution to the advancement of related technologies. In particular, one of the fields where the high price of the hole amp; 8208;transporting materials may become an obstacle toward successful commercialization is perovskite solar cells. Herein, enamine amp; 8208;based materials that are capable of undergoing cross amp; 8208;linking due to the presence of two vinyl groups are synthesized. It is shown that new compounds can be thermally polymerized, making the films resistant to organic solvents. This can allow the use of a wet amp; 8208;coating process for the deposition of the perovskite absorber film, without the need for orthogonal solvents. Cross amp; 8208;linked films are used in perovskite solar cells, and, upon optimization of the film thickness, the highest power conversion efficiency of 18.1 is demonstrated

Solar cells based on metal halide perovskites have attracted tremendous attention due to the rapid increase in performance of single junctions and tandem solar cells. Recently, highest perovskite silicon tandem efficiencies are realized with front side polished silicon wafers or adapted microstructure of textured silicon solar cells. One way to integrate perovskite top cells on typical micrometer sized pyramidal structures, is conformal vacuum based perovskite deposition. Herein, fully vacuum based perovskite solar cells are developed on top of random pyramidal microtextured glass substrates with a pyramid size up to 9 mu m. This method allows improvement of the light management of the textured perovskite solar cell and resembles the typical pyramid topography of silicon solar cells as a step toward monolithic tandem integration. Moreover, to improve the quality of the perovskite on the textured substrates, three different methylammonium lead iodide MAPbI 3 films are tested by adjusting the rate ratio of the precursors. Optimized ratios for textured substrates with higher PbI2 rates enable a transient photoluminescence decay time above 0.75 mu s approaching that of planar substrates at around 1.2 mu s. Finally, a efficiency over 15 is achieved, which is, to the best of our knowledge, the first reported device on microscopically textured glass by co evaporated ion

The effect of sodium doping in NiO as a contact layer for perovskite solar cells is investigated. A combined X-ray diffraction and X-ray photoelectron spectroscopy analysis reveals that Na+ mostly segregates as NaOx/NaCl species around NiO crystallites, with the effect of reducing interface capacitance as revealed by impedance spectroscopy. Inspired by this finding, the NiO/perovskite interface in perovskite solar cells is modified via insertion of an ultrathin NaCl interlayer, which increases the NiO work-function by 0.3 eV. This leads to an increase of power conversion efficiency, approaching 18%, and open-circuit voltage due to a remarkable suppression of surface recombination, as revealed by photoluminescence analysis and light intensity–dependent electrical measurements.

The rapid rise of perovskite solar cells (PSCs) is increasingly limited by the available charge-selective contacts. This work introduces two new hole-selective contacts for p–i–n PSCs that outperform all typical p-contacts in versatility, scalability and PSC power-conversion efficiency (PCE). The molecules are based on carbazole bodies with phosphonic acid anchoring groups and can form self-assembled monolayers (SAMs) on various oxides. Besides minimal material consumption and parasitic absorption, the self-assembly process enables conformal coverage of arbitrarily formed oxide surfaces with simple process control. The SAMs are designed to create an energetically aligned interface to the perovskite absorber without non-radiative losses. For three different perovskite compositions, one of which is prepared by co-evaporation, we show dopant-, additive- and interlayer-free PSCs with stabilized PCEs of up to 21.1%. Further, the conformal coverage allows to realize a monolithic CIGSe/perovskite tandem solar cell with as-deposited, rough CIGSe surface and certified efficiency of 23.26% on an active area of 1 cm2. The simplicity and diverse substrate compatibility of the SAMs might help to further progress perovskite photovoltaics towards a low-cost, widely adopted solar technology.

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 structural phases and optoelectronic properties of coevaporated CsPbI 3 thin films with a wide range of [CsI]/[PbI 2 ] compositional ratios are investigated using high throughput experimentation and gradient samples. It is found that for CsI-rich growth conditions, CsPbI 3 can be synthesized directly at low temperature into the distorted perovskite γ-CsPbI 3 phase without detectable secondary phases. In contrast, PbI 2 -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 cm 2 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.

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 mole cule 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 tex tured 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

We present a new strategy for highly efficient perovskite/CIGSe monolithic tandem solar cells, fabricated directly on top of a rough CIGSe surface. This was enabled by conformally depositing the metal oxide NiOx by atomic layer deposition, as confirmed by TEM/EDX measurements. The resulting limiting NiOx/perovskite interface was improved by spin-coating additional thin layer of p-type polymer PTAA, thus forming a NiOx/PTAA hole selective bilayer. The fabricated tandem device has a 21.6% power conversion efficiency on 0.778 cm2, stable over 10 minutes of maximum power point tracking. The device performance is further analyzed by absolute photoluminescence measurements from which a VOC contribution of each subcell to the tandem VOC can be estimated.