Hang Hu

The recent tremendous progress in monolithic perovskite-based double-junction solar cells is just the start of a new era of ultra-high-efficiency multi-junction photovoltaics. We report on triple-junction perovskite–perovskite–silicon solar cells with a record power conversion efficiency of 24.4%. Optimizing the light management of each perovskite sub-cell (∼1.84 and ∼1.52 eV for top and middle cells, respectively), we maximize the current generation up to 11.6 mA cm−2. Key to this achievement was our development of a high-performance middle perovskite sub-cell, employing a stable pure-α-phase high-quality formamidinium lead iodide perovskite thin film (free of wrinkles, cracks, and pinholes). This enables a high open-circuit voltage of 2.84 V in a triple junction. Non-encapsulated triple-junction devices retain up to 96.6% of their initial efficiency if stored in the dark at 85 °C for 1081 h.

Optical interference filters (OIFs) are vital components for a wide range of optical and photonic systems. They are pivotal in controlling spectral transmission and reflection upon demand. OIFs rely on optical interference of the incident wave at multilayers, which are fabricated with nanometer precision. Here, we demonstrate that these requirements can be fulfilled by inkjet printing. This versatile technology offers a high degree of freedom in manufacturing, as well as cost-affordable and rapid-prototyping features from the micron to the meter scale. In this work, via rational ink design and formulation, OIFs were fully inkjet printed in ambient conditions. Longpass, shortpass, bandpass, and dichroic OIFs were fabricated, and precise control of the spectral response in OIFs was realized. Subsequently, customized lateral patterning of OIFs by inkjet printing was achieved. Furthermore, upscaling of the printed OIFs to A4 size …

Formamidinium lead iodide (FAPbI3) has emerged as one of the most promising perovskite semiconductors for perovskite solar cells (PSCs), demonstrating high power conversion efficiency (PCE) and good stability. However, only a few reports address the scalable processing and fabrication of FAPbI3 perovskite solar modules. Here, we report a void-free perovskite-buried interface in p-i-n-based PSCs, which enables us to upscale lab-scale solar cells (<1 cm2) to mini-module dimensions (>10 cm2). An innovative combination of a moderate N2 flow during vacuum-assisted growth (VAG) control of the perovskite thin films as well as the employment of MACl as an additive eliminates interfacial voids in blade-coated large-area FAPbI3 layers, enabling respective PCEs of 20.0% and 18.3% in blade-coated PSCs (0.105 cm2) and fully scalable modules (aperture area of 12.25 cm2 and geometric fill factor of 96.3 …

Perovskite gain materials can sustain continuous-wave lasing at room-temperature. A first step toward the unachieved goal of electrically excited lasing would be an improvement in gain when electrical stimulation is added to the optical. However, to date, electrical stimulation supplementing optical has reduced gain performance. We find that amplified spontaneous emission (ASE) in a CsPbBr3 perovskite light-emitting diode (LED) held under invariant subthreshold optical excitation can be turned on/off by the addition/removal of an electric field. A positive bias voltage leads to a factor of 3 reduction in the optical ASE threshold, the cause of which can be attributed to an enhancement of the radiative rate. The slow components (10 s time scale) of the modulation in the photoluminescence and ASE when the voltage is changed suggest that the relocation of mobile ions trigger the increased radiative rate and observed …

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 (RA) ground such as dark sandstone (RA = 9%). The EY gain for bifacial cells rises to a maximum of 40–50% for ground modeled as a perfect reflector (RA = 100 …

Transparent photovoltaics provide diverse levels of average visible transmittance (AVT) along with concurrent light harvesting, making glass façades and windows accessible for photovoltaics. However, improvements in power conversion efficiency (PCE) and aesthetics are required to enhance commercial viability and public acceptance. This work presents the scalable fabrication of efficient micro-patterned translucent perovskite photovoltaics at optical qualities suited for building integration. Optimized laser-scribed transparent areas (25 μm) mitigate detrimental effects on electrical performance, featuring perovskite solar cells with 44% AVT and demonstrating industrial glass quality through neutral color rendering (CRI 97) and only 3% haze. Highlighting scalability, submodules yield PCEs of 9.0% at 32% AVT (4 cm2 aperture area). The transfer to two-terminal perovskite–perovskite tandem solar cells exhibiting …

The recent development of solution‐processed perovskite thin films over micrometer‐sized textured silicon bottom solar cells enables tandem solar cells with power conversion efficiencies > 30%. Next to improved light harvesting, textured silicon wafers are the industrial standard. To achieve high performance, the open‐circuit voltage losses that occur when fabricating perovskite solar cells over such textures need to be mitigated. This study provides a practical guideline to discriminate and address the voltage losses at the interfaces as well as in the bulk of solution‐processed double cation perovskite thin films using photoluminescence quantum yield measurements. Furthermore, the origin of these losses is investigated via morphological, microstructural, and compositional analysis and present possible mitigation strategies. The guideline will be beneficial for scientists working on randomly textured surfaces and …

Monolithic all-perovskite tandem photovoltaics promise to combine low-cost and high-efficiency solar energy harvesting with the advantages of all-thin-film technologies. To date, laboratory-scale all-perovskite tandem solar cells have only been fabricated using non-scalable fabrication techniques. In response, this work reports on laser-scribed all-perovskite tandem modules processed exclusively with scalable fabrication methods (blade coating and vacuum deposition), demonstrating power conversion efficiencies up to 19.1% (aperture area, 12.25 cm2; geometric fill factor, 94.7%) and stable power output. Compared to the performance of our spin-coated reference tandem solar cells (efficiency, 23.5%; area, 0.1 cm2), our prototypes demonstrate substantial advances in the technological readiness of all-perovskite tandem photovoltaics. By means of electroluminescence imaging and laser-beam-induced current …

Perovskite/silicon tandem photovoltaics have attracted enormous attention in science and technology over recent years. In order to improve the performance and stability of the technology, new materials and processes need to be investigated. However, the established sequential layer deposition methods severely limit the choice of materials and accessible device architectures. In response, a novel lamination process that increases the degree of freedom in processing the top perovskite solar cell (PSC) is proposed. The very first prototypes of laminated monolithic perovskite/silicon tandem solar cells with stable power output efficiencies of up to 20.0% are presented. Moreover, laminated single‐junction PSCs are on par with standard sequential layer deposition processed devices in the same architecture. The numerous advantages of the lamination process are highlighted, in particular the opportunities to …

Monolithic two-terminal (2T) perovskite/CuInSe2 (CIS) tandem solar cells (TSCs) combine the promise of an efficient tandem photovoltaic (PV) technology with the simplicity of an all-thin-film device architecture that is compatible with flexible and lightweight PV. In this work, we present the first-ever 2T perovskite/CIS TSC with a power conversion efficiency (PCE) approaching 25% (23.5% certified, area 0.5 cm2). The relatively planar surface profile and narrow band gap (∼1.03 eV) of our CIS bottom cell allow us to exploit the optoelectronic properties and photostability of a low-Br-containing perovskite top cell as revealed by advanced characterization techniques. Current matching was attained by proper tuning of the thickness and bandgap of the perovskite, along with the optimization of an antireflective coating for improved light in-coupling. Our study sets the baseline for fabricating efficient perovskite/CIS TSCs …

Interfacial engineering is the key to high‐performance perovskite solar cells (PSCs). While a wide range of fullerene interlayers are investigated for Pb‐based counterparts with a bandgap of >1.5 eV, the role of fullerene interlayers is barely investigated in Sn‐Pb mixed narrow‐bandgap (NBG) PSCs. In this work, two novel solution‐processed fullerene derivatives are investigated, namely indene‐C60‐propionic acid butyl ester and indene‐C60‐propionic acid hexyl ester (IPH), as the interlayers in NBG PSCs. It is found that the devices with IPH‐interlayer show the highest performance with a remarkable short‐circuit current density of 30.7 mA cm−2 and a low deficit in open‐circuit voltage. The reduction in voltage deficit down to 0.43 V is attributed to reduced non‐radiative recombination that the authors attribute to two aspects: 1) a higher conduction band offset of ≈0.2 eV (>0 eV) that hampers charge‐carrier‐back …

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 …

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%.

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 …

All-inorganic perovskites exhibit interesting properties and unprecedented stability compared to organic-inorganic hybrid lead halide perovskites. This work focuses on depositing and characterizing cesium lead bromide (CsPbBr_3) thin films and determining their complex optical constants, which is a key requirement for photovoltaic device design. CsPbBr_3 thin films are synthesized via the solution method followed by a hot-embossing step to reduce surface roughness. Variable angle spectroscopic ellipsometry measurements are then conducted at three angles (45°, 55°, and 65°) to obtain the ellipsometric parameters psi (Ψ) and delta (Δ). For the present model, bulk planar CsPbBr_3 layer is described by a one-dimensional graded index model combined with the mixture of one Tauc-Lorentz oscillator and two Gaussian oscillators, while an effective medium approximation with 50% air void is adopted to describe …

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 …