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We discuss the generation and the long-time persistence of entanglement in open two-qubit systems whose reduced dissipative dynamics is not a priori engineered but is instead subjected to filtering and Markovian feedback. In particular, we analytically study (1) whether the latter operations may enhance the environment capability of generating entanglement at short times and (2) whether the generated entanglement survives in the long-time regime. We show that, in the case of particularly symmetric Gorini–Kossakowski–Sudarshan–Lindblad it is possible to fully control the convex set of stationary states of the two-qubit reduced dynamics, therefore the asymptotic behaviour of any initial two-qubit state. We then study the impact of a suitable class of feed-back operations on the considered dynamics.

y High specific power, high stowed packing efficiency, low processing cost, and high tolerance against environmental threats (high energy and charged particle radiation) make perovskite solar cell (PSC) a promising candidate for power generation in space. However, vacuum, as encountered in space, causes perovskite outgassing, raising concern for its long-term stability. In this work, we find that PSCs (ITO/SnO2/perovskite/Spiro-MeOTAD/Au) degrade ten times faster upon reducing the pressure from 9 x 10(4) to 5 x 10(3) Pa during operation, due to acceleration of the perovskite transformation and ion migration. Gas permeability of the layers atop perovskite and mobile ion-induced chemical reactions at charge transporting layers and related interfaces are two critical factors. We develop a PSC structure (ITO/PTAA/perovskite/PCBM/ZnO/AZO/[Ni/Al grid]) that effectively mitigates vacuum and illumination-induced degradation pathways, enabling PSCs to realize a low PCE loss rate of 0.007%/h over 1,037 h at the maximum power point under 100 mW cm(-2) illumination at 5 x 10(3) Pa.

Over the last years, the operational stability of perovskite solar cells has been significantly improved by compositional engineering, interface modification, and improved encapsulation techniques. However, irreversible degradation is still ubiquitously observed during the first 1000 hours of operation, particularly at elevated temperatures. In this work, we elucidate a major mechanism controlling this degradation. For that, formamidinium lead iodide-based perovskite solar cells were stressed under continuous 1 sun illumination at 80 °C in N2, before extensive characterization of their microstructure and composition. The cell active area and hence the photocurrent are found to decrease with time due to the growth of porous PbI2-rich regions. This degradation was observed to originate from a few seed points in the perovskite bulk rather than from the interfaces with the charge-selective layers or from the cell edges. I2 vapor, first released at these defective points and then further released from the decomposition of the perovskite exposed to this vapor, controls the degradation process. Furthermore, this autocatalytic degradation process is shown to locally rupture the top electrode due to vapor pressure build-up. In addition to highlighting the detrimental influence of residual PbI2, we show that such a degradation pathway can be alleviated by reducing the methylammonium and/or iodine content, providing a path to more stable perovskite solar cells.

Four-terminal (4-T) tandem solar cells (e.g., perovskite/CuInSe2 (CIS)) rely on three transparent conductive oxide electrodes with high mobility and low free carrier absorption in the near-infrared (NIR) region. In this work, a reproducible In2O3:H (IO:H) film deposition process is developed by independently controlling H2 and O2 gas flows during magnetron sputtering, yielding a high mobility value up to 129 cm2 V–1 s–1 in highly crystallized IO:H films annealed at 230 °C. Optimization of H2 and O2 partial pressures further decreases the crystallization temperature to 130 °C. By using a highly crystallized IO:H film as the front electrode in NIR-transparent perovskite solar cell (PSC), a 17.3% steady-state power conversion efficiency and an 82% average transmittance between 820 and 1300 nm are achieved. In combination with an 18.1% CIS solar cell, a 24.6% perovskite/CIS tandem device in 4-T configuration is demonstrated. Optical analysis suggests that an amorphous IO:H film (without postannealing) and a partially crystallized IO:H film (postannealed at 150 °C), when used as a rear electrode in a NIR-transparent PSC and a front electrode in a CIS solar cell, respectively, can outperform the widely used indium-doped zinc oxide (IZO) electrodes, leading to a 1.38 mA/cm2 short-circuit current (Jsc) gain in the bottom CIS cell of 4-T tandems.

Flexible perovskite solar cells (PSCs) hold great promise for the low-cost roll-to-roll production of lightweight single- and multijunction photovoltaic devices. Among the different deposition methods used for the perovskite absorber, the two-step hybrid vacuum-solution approach enables precise control over the thickness and morphology of PbI2. However, efficient conversion to perovskite is limited by diffusion of the organic cations in the compact lead halide layer. Herein, a multistage absorber deposition is developed by thermal evaporation of PbI2 and spin coating of CH3NH3I (MAI). The process relies on the different types of growth of vacuum-deposited PbI2 onto amorphous and crystalline surfaces. This approach represents a way to effectively increase the absorber thickness while tackling the limited MAI diffusion in the compact PbI2 film via a two-step deposition method. The efficiency of flexible PSCs is improved from 14.2 to 15.8% with multistage deposition. Furthermore, the use of an amorphous transparent conductive oxide (TCO), InZnO, enhances the mechanical resistance against bending with respect to conventional crystalline TCO-based flexible devices. Near-infrared transparent flexible PSCs are developed with an efficiency of 14.0% and average transmittance of ~74% between 800 and 1000 nm. Flexible perovskite/CIGS thin-film tandem devices are demonstrated with an efficiency of 19.6% measured in the four-terminal configuration. The efficiency of printable solar cells can be increased using a production method developed by researchers in Switzerland. Hybrid perovskites, a material that combines organic and inorganic components, are emerging as a competitive alternative to silicon for producing solar cells. One of their major advantages is that perovskite devices can be created on flexible substrates, making them compatible with a technology that prints devices on a roll of plastic. This means they can be cheaply mass produced, however their conversion efficiency needs to be improved. Stefano Pisoni and colleagues from the Swiss Federal Laboratories for Materials Science and Technology in Duebendorf constructed a perovskite solar cell using a two-step method that combined thermally evaporated lead iodide and a coating of methylammonium iodide. This design enabled better diffusion of the organic cations, which improved the device efficiency. Flexible perovskite solar cell with an efficiency of 15.8 % via tailoring of vacuum-deposited PbI2 growth morphology has been achieved. We demonstrated superior mechanical bending stability using amorphous TCO (retaining 80 % of the initial efficiency after 1000 bending cycles at 4 mm bending radius). Flexible NIR-transparent perovskite solar cell with an efficiency of 14.0 % and average transmittance of ~74 % between 800 and 1000 nm has been developed. Eventually, we proved a flexible perovskite/CIGS tandem solar cell with an efficiency of 19.6 % measured in four-terminal configuration.

The unique properties of halide perovskites are suitable for low-cost high-efficiency photovoltaic applications. For commercialization of this technology, it is pivotal to upscale towards solar modules. Monolithic interconnection of solar cells is a necessary step for realization of thin-film solar modules and the laser scribing of the constituent layers with well-defined profiles of high accuracy is a promising approach for high speed processing. Here the laser ablation and scribing of methylammonium lead iodide perovskite (CH3NH3PbI3: MAPbI3) layers are investigated. Nanosecond (ns) and picosecond (ps) laser pulses were used to ablate and scribe MAPbI3 films on FTO/glass by irradiation from the film- and the glass-side. Depending on the irradiation configuration laser ablation or lift-off delamination was determined to be the dominating mechanism of thin-film removal. Various surface modifications such as film smoothening and decomposition of the MAPbI3 have been observed, especially when nanosecond laser pulses are used. The complete removal of the MAPbI3, film without damaging the FTO/substrate, has been achieved for all studied laser sources.

The possibility of growing perovskite solar cells on flexible substrates can be seen as an exciting opportunity, allowing high throughput roll-to-roll manufacturing with a low embodied energy, and creating new applications in buildings, vehicles, portable electronics and internet-of-things based devices. Flexible perovskite solar cells have previously been developed on polymer substrates such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) which are vulnerable to the ingress of moisture. Here we report the development of flexible perovskite solar cells grown on a typical transparent front sheet which is generally used to encapsulate flexible Cu(In,Ga)Se2 (CIGS) solar cells. This type of substrate displays an ultra-low water vapor transmission rate and good UV blocking properties. Perovskite solar cells, grown on such flexible front sheets coated with a highly transparent conducting ZnO:Al (AZO) electrode and vacuum processed ZnO/C60 electron transport multilayer, yield 13.2% and 10.9% stabilized efficiencies for areas of 0.15 cm2 and 1.03 cm2, respectively. The substitution of an opaque rear contact with the transparent electrode enables the realization of flexible NIR-transparent perovskite solar cells with efficiencies above 12%. These devices display an average transmittance of 78% between 800 and 1000 nm and enable the development of 4-terminal polycrystalline all-thin-film flexible perovskite/CIGS tandem devices. In a first proof of concept 18.2% efficiency is obtained.

Compositional grading has been widely exploited in highly efficient Cu(In,Ga)Se2, CdTe, GaAs, quantum dot solar cells, and this strategy has the potential to improve the performance of emerging perovskite solar cells. However, realizing and maintaining compositionally graded perovskite absorber from solution processing is challenging. Moreover, the operational stability of graded perovskite solar cells under long‐term heat/light soaking has not been demonstrated. In this study, a facile partial ion‐exchange approach is reported to achieve compositionally graded perovskite absorber layers. Incorporating compositional grading improves charge collection and suppresses interface recombination, enabling to fabricate near‐infrared‐transparent perovskite solar cells with power conversion efficiency of 16.8% in substrate configuration, and demonstrate 22.7% tandem efficiency with 3.3% absolute gain when mechanically stacked on a Cu(In,Ga)Se2 bottom cell. Non‐encapsulated graded perovskite device retains over 93% of its initial efficiency after 1000 h operation at maximum power point at 60 °C under equivalent 1 sun illumination. The results open an avenue in exploring partial ion‐exchange to design graded perovskite solar cells with improved efficiency and stability.

Four-terminal (4-T) tandem solar cells (e.g., perovskite/CuInSe2 (CIS)) rely on three transparent conductive oxide electrodes with high mobility and low free carrier absorption in the near-infrared (NIR) region. In this work, a reproducible In2O3:H (IO:H) film deposition process is developed by independently controlling H2 and O2 gas flows during magnetron sputtering, yielding a high mobility value up to 129 cm2 V–1 s–1 in highly crystallized IO:H films annealed at 230 °C. Optimization of H2 and O2 partial pressures further decreases the crystallization temperature to 130 °C. By using a highly crystallized IO:H film as the front electrode in NIR-transparent perovskite solar cell (PSC), a 17.3% steady-state power conversion efficiency and an 82% average transmittance between 820 and 1300 nm are achieved. In combination with an 18.1% CIS solar cell, a 24.6% perovskite/CIS tandem device in 4-T configuration is demonstrated. Optical analysis suggests that an amorphous IO:H film (without postannealing) and a partially crystallized IO:H film (postannealed at 150 °C), when used as a rear electrode in a NIR-transparent PSC and a front electrode in a CIS solar cell, respectively, can outperform the widely used indium-doped zinc oxide (IZO) electrodes, leading to a 1.38 mA/cm2 short-circuit current (Jsc) gain in the bottom CIS cell of 4-T tandems. This work was supported by funding from the Swiss Federal Office of Energy (SFOE)-BFE (project no. SI/501805-01), Swiss National Science Foundation (SNF)-Bridge (project no. 20B2-1_176552/1), and the European Research Council (ERC) under EU’s Horizon 2020 Research and Innovation Program (grant agreement no. 681312). We thank Dr. Yi Hou for the supply of the antireflection foil.

Knowledge of the absorber bandgap is often needed for assessing the junction quality of a thin film solar cell, for example when computing the open-circuit voltage deficit. The bandgap is typically estimated from the routine measurement of the external quantum efficiency (EQE) of finished devices. However the extraction becomes ambiguous in the case of very thin absorbers, or in presence of bandgap gradients or collection issues of charge carriers. This work reviews several methods for the determination of the bandgap from EQE measurements and discusses their validity conditions. The numerical results are compared based on experimental EQE of several different thin film solar cells such as CuInGaSe2, CuInSe2, CdTe, CuZnSnSe and perovskite, and systematic trends are identified. Numerical simulations are also performed to illustrate the behavior of the different bandgap extraction methods in presence of a bandgap gradient and different magnitudes of the exponential tail states.

The development of highly efficient lightweight flexible perovskite solar cells (PSCs) opens the way to high-throughput roll-to-roll manufacturing processes and new applications such as building integration and mobile products. Flexible PSCs are generally realized on small areas (< 0.2 cm(2)), far from technology commercialization where modules-scale is necessary. In this work, we demonstrate highly efficient n-i-p PSCs grown on flexible substrates by proper interface engineering for improved electron extraction. We compared spin coated PEIE and vacuum deposited LiF as interlayers between Al-doped ZnO, as transport conductive oxide (TCO), and thermally evaporated C-60, as electron transport layer (ETL). Once interlayers are applied, we observed a favorable band bending at TCO interface which results in enhanced charge extraction and lower recombination losses. We achieved flexible PSCs with stabilized efficiencies of 14.8%, both with PEIE and LiF interfacial modifications., In addition, we developed a flexible perovskite mini-module with stabilized efficiency of 10.5% onto an aperture area larger than 10 cm(2). The monolithic interconnections are entirely obtained by highly accurate and reliable laser scribing methods. A geometric fill factor as high as similar to 94% is achieved, with a dead area width of similar to 250 mu m.