Energy Yield Modeling of Bifacial All‐Perovskite Two‐Terminal Tandem Photovoltaics

All-perovskite two-terminal tandem photovoltaics offer high power conversion efficiencies (PCEs) that can surpass the limits of single-junction photovoltaics. In this study, energy yield (EY) simulations are performed to assess the performance of bifacial all-perovskite tandem solar cells. Under standard test conditions, in the absence of albedo, bifacial tandems demonstrate a 4.9% relative lower PCE compared to equivalent monofacial tandems due to transparency losses at the semitransparent rear side. However, under realistic irradiation conditions, albedo irradiation leads to an enhancement in EY for bifacial cells. This enhancement enables bifacial cells to produce more energy than monofacial cells, even over relatively low average reflectance (R$_A$) ground such as dark sandstone (R$_A$ = 9%). The EY gain for bifacial cells rises to a maximum of 40–50% for ground modeled as a perfect reflector (R$_A$ = 100%), accompanied by a shift in optimum top subcell bandgap to 1.56 eV. This shift is of particular interest as low-bandgap perovskite semiconductors (with lower bromide concentrations) offer enhanced stability under realistic operation conditions. Finally, this work presents a route to increase the PCE of simulated monofacial and bifacial cells, to 31.9% and 30.8%, respectively, by optimizing the optical and electrical performance of the cells

Danger in the Dark: Stability of Perovskite Solar Cells with Varied Stoichiometries and Morphologies Stressed at Various Conditions

Long-term stability of perovskite solar cells (PSCs) remains a bottleneck for commercialization. While studies of PSCs stoichiometry and morphology with regard to performance are prevalent, understanding of these factors influence on long-term stability is lacking. In this work, we evaluate the impact of stoichiometry and morphology on the long-term stability of cesium formamidinium based PSCs. We demonstrate that the lead iodide (PbI2) to formamidinium iodide (FAI) ratio influences stability under various stress factors (elevated temperature and light). A high molar ratio (PbI2/FAI >1.1) in the perovskite precursor displays drastic degradation under ISOS-L1 (100 mW/cm2, 25 °C, maximum power point tracking) conditions. However, post-degradation analysis contradicts these results. Devices with PbI2/FAI ≤1.1 are stable under light but intermittent current density-voltage characterizations indicate that device performance decreases during storage in the dark. Migration of iodide (I-) to the electron transport layer (ETL) and iodine vacancies (VI-+) to the hole transport layer (HTL) forms localized shunts in the absorber layer. Pinhole formation, surrounded by FA+ rich regions, explains the extent of damage in comparably aged films. In summary, this work emphasizes the importance of reporting stability under different stress conditions, coupled with post degradation and dark recovery analysis of PSCs to better understand the complexities of perovskite instability under real-life conditions such as expected during outdoor operation

In Situ Process Monitoring and Multichannel Imaging for Vacuum‐Assisted Growth Control of Inkjet‐Printed and Blade‐Coated Perovskite Thin‐Films

Vacuum-assisted growth (VAG) control is one of the most promising methods for controlling nucleation and crystallization of printed and coated large area lead halide perovskite-based layers for optoelectronics. To coat or print homogeneous high-quality perovskite thin-films at high fabrication yield, real-time process monitoring of the VAG is pivotal. In response, a 2.1-megapixel multichannel photoluminescence (PL) and reflection imaging system is developed and employed for the simultaneous spatial in situ analysis of drying, nucleation, and crystal growth during VAG and subsequent thermal annealing of inkjet-printed and blade-coated perovskite thin-films. It is shown that the VAG process, for example, evacuation rate and time, affects the film formation and provide detailed insight into traced PL and reflection transients extracted from sub-second videos of each channel. Based on correlative analysis between the transients and, for example, perovskite ink composition, wet-film thickness, or evacuation time, key regions which influence crystal quality, film morphology, and are base for prediction of solar cell performance are identified

Intensity Dependent Photoluminescence Imaging for In‐Line Quality Control of Perovskite Thin Film Processing

Large area fabrication of high-quality polycrystalline perovskite thin filmsremains one of the key challenges for the commercial readiness of perovskitephotovoltaic (PV). To enable high-throughput and high-yield processing,reliable and fast in-line characterization methods are required. The presentwork reports on a non-invasive characterization technique based onintensity-dependent photoluminescence (PL) imaging. The change in PLintensity as a function of excitation power density can be approximated by apower-law with exponent k, which is a useful quality indicator for theperovskite layer, providing information about the relative magnitudes ofradiative and non-radiative recombination. By evaluating k-parameter mapsinstead of more established PL intensity images, 2D information is obtainedthat is robust to optically induced artifacts such as intensity variations inexcitation and reflection. Application to various half stacks of a perovskitesolar cell showcase its ability to determine the importance of the interfacebetween the charge transporting and perovskite layers. In addition, thek-parameter correlates to the bulk passivation concentration, enabling rapidassessment of open-circuit voltage variations in the range of 20 mV.Considering expected improvements in data acquisition speed, the presentedk-imaging method will possibly be obtained in real-time, providing large-areaquality control in industrial-scale perovskite PV production

Laminated Perovskite Photovoltaics: Enabling Novel Layer Combinations and Device Architectures

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

Triple-cation low-bandgap perovskite thin-films for high-efficiency four-terminal all-perovskite tandem solar cells

All-perovskite multi-junction photovoltaics, comprised of a wide-bandgap (WBG) and a low-bandgap (LBG) perovskite solar cell (PSC), has opened a new window to cost-effective yet highly efficient solar cells (>33%). However, the poor operational stability of LBG PSCs is a major obstacle to the technological advance of all-perovskite tandem solar cells (all-PTSC). This study demonstrates that introducing minute quantities of Cs (1-10%) into the LBG FA0.8MA0.2Sn0.5Pb0.5I3 perovskite semiconductors (Eg = 1.26 eV) significantly improves the operational photo-stability of the corresponding LBG PSCs, due to a reduction of residual nanosized SnyPb(1-y)I2 aggregates, resulting in a beneficial stoichiometric composition. For an optimal concentration of Cs (2.5%) in the investigated range, the LBG PSCs attain remarkable power conversion efficiency (PCE) as high as 18.2% and maintain up to 92% of their initial power output after two hours under simulated one sun illumination. By mechanically stacking high-performance LBG bottom PSCs with semi-transparent top PSCs (Eg = 1.65 eV), four-terminal all-PTSCs with high PCE of 23.6% are attainable. This journal isWe acknowledge support by the KIT-Publication Fund of the Karlsruhe Institute of Technology. We would like to thank Dirk Hauschild (KIT) and Lothar Weinhardt (KIT) for XPS measurements. S. M. would like to acknowledge the nancial support from DAAD (Deutscher Akademischer Austauschdienst/German academic exchange service) for her doctoral research work under personal reference number 91621525. The nancial support by Alexander von Humboldt (Georg Forster Research Fellowship), German Federal Ministry of Education and Research (BMBF) through PRINTPERO (03SF0557A) project, German Federal Ministry for Economic Affairs and Energy (CAPITANO, funding code: 03EE1038B), the Initiating and Networking funding of Helmholtz Association HYIG of U.W.P. (VH-NG-1148), Helmholtz Energy Materials Foundry (HEMF), PEROSEED (ZT-0024), Science and Technology of Nanostructures (STN), and Karlsruhe School of Optics & Photonics (KSOP) is gratefully acknowledged. T. D. acknowledges the nancial support of a Postdoc Fellowship from the Australian Centre for Advanced Photovoltaics (ACAP). Part of the experiment was performed at the Australian National Fabrication Facility (ANFF) ACT Node

In2_{2}O3_{3}:H-Based Hole-Transport-Layer-Free Tin/Lead Perovskite Solar Cells for Efficient Four-Terminal All-Perovskite Tandem Solar Cells

Narrow-band gap (NBG) Sn–Pb perovskites with band gaps of ∼1.2 eV, which correspond to a broad photon absorption range up to ∼1033 nm, are highly promising candidates for bottom solar cells in all-perovskite tandem photovoltaics. To exploit their potential, avoiding optical losses in the top layer stacks of the tandem configuration is essential. This study addresses this challenge in two ways (1) removing the hole-transport layer (HTL) and (2) implementing highly transparent hydrogen-doped indium oxide In2O3:H (IO:H) electrodes instead of the commonly used indium tin oxide (ITO). Removing HTL reduces parasitic absorption loss in shorter wavelengths without compromising the photovoltaic performance. IO:H, with an ultra-low near-infrared optical loss and a high charge carrier mobility, results in a remarkable increase in the photocurrent of the semitransparent top and (HTL-free) NBG bottom perovskite solar cells when substituted for ITO. As a result, an IO:H-based four-terminal all-perovskite tandem solar cell (4T all-PTSCs) with a power conversion efficiency (PCE) as high as 24.8% is demonstrated, outperforming ITO-based 4T all-PTSCs with PCE up to 23.3%

Spontaneous Enhancement of the Stable Power Conversion Efficiency in Perovskite Solar Cells

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 dark. Thus far, effects underlying this spontaneous enhancement 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 the 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, initially-present low-energy states are identified that disappear over a storage period of a few days. Furthermore, trap states probed by thermally stimulated current technique exist in pristine PSCs and strikingly decrease for stored devices. In addition, ideality factor approaches unity and X-ray diffraction analyses show a lattice strain relaxation over the same period of time. These observations indicate that spontaneous enhancement of the 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 absolute PCE increase initiated by spontaneous enhancement for developing high-efficiency PSCs

2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

Wide-bandgap perovskite solar cells (PSCs) with optimal bandgap (E$_{g}$) and high power conversion efficiency (PCE) are key to high-performance perovskite-based tandem photovoltaics. A 2D/3D perovskite heterostructure passivation is employed for double-cation wide-bandgap PSCs with engineered bandgap (1.65 eV ≤ E$_{g}$ ≤ 1.85 eV), which results in improved stabilized PCEs and a strong enhancement in open-circuit voltages of around 45 mV compared to reference devices for all investigated bandgaps. Making use of this strategy, semitransparent PSCs with engineered bandgap are developed, which show stabilized PCEs of up to 25.7% and 25.0% in fourterminal perovskite/c-Si and perovskite/CIGS tandem solar cells, respectively. Moreover, comparable tandem PCEs are observed for a broad range of perovskite bandgaps. For the first time, the robustness of the four-terminal tandem configuration with respect to variations in the perovskite bandgap for two state-of-the-art bottom solar cells is experimentally validated

Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA0.8_{0.8}MA0.2_{0.2}Sn0.5_{0.5}Pb0.5_{0.5}I3_{3}) for All‐Perovskite Tandem Solar Cells

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