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HighlightsRecent progress of efficiency and long-term stability for perovskite solar cells, and the development of perovskite-based tandem solar cells are described.The progress of lead-free perovskite solar cells and their potential for industrial production are discussed in detail.The current status, ongoing challenges, and the future outlooks of perovskite solar cells are highlighted.Perovskite solar cells (PSCs) emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world. Both the efficiency and stability of PSCs have increased steadily in recent years, and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step. This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency, stability, perovskite-based tandem devices, and lead-free PSCs. Moreover, a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

Tin perovskite solar cells (TPSCs) have triggered intensive research as a promising candidate for lead-free perovskite solar cells. However, it is still challenging to obtain efficient and stable TPSCs because of the low defects formation energy and the oxidation of bivalent tin; Here, we report a TPSC with a stable amorphous-polycrystalline structure, which is composed of a tin triple-halide amorphous layer and cesium-formamidinium tin iodide polycrystals. This structure effectively blocks the outside oxygen, moisture and also suppresses the ion diffusion inside the devices. In addition, its energy level benefits the charge extraction and transport in TPSCs. This design enabled us to obtain the certified quasi-steady-state efficiency over 10% for TPSCs from an accredited certification institute. The cell was stable, maintaining 95% of the initial PCE after operation at the maximum power point under AM 1.5 G simulated solar light (100 mWcm −2 ) for 1000 hours. Tin based perovskite solar cells could be promising replacements for lead based counterparts due to their lower toxicity, but their efficiencies are much lower. Here, Liu et al. report stable tin based perovskite solar cells with efficiency over 10% by designing amorphous-polycrystalline nanostructures.

HighlightsA novel strategy to further improve the efficiency of lead-free tin perovskite solar cells by carefully controlling the built-in electric field in the absorber is described.A promising efficiency of 13.82% was obtained based on the formamidinium tin iodide (FASnI3) perovskite solar cells with a vertical Sn2+ gradient and an enhanced electric field.The solar cell with a heterogeneous FASnI3 absorber is ultrastable, maintaining over 13% efficiency after operation under 1-sun illumination for 1,000 h in air.Lead-free tin perovskite solar cells (PSCs) have undergone rapid development in recent years and are regarded as a promising eco-friendly photovoltaic technology. However, a strategy to suppress charge recombination via a built-in electric field inside a tin perovskite crystal is still lacking. In the present study, a formamidinium tin iodide (FASnI3) perovskite absorber with a vertical Sn2+ gradient was fabricated using a Lewis base-assisted recrystallization method to enhance the built-in electric field and minimize the bulk recombination loss inside the tin perovskites. Depth-dependent X-ray photoelectron spectroscopy revealed that the Fermi level upshifts with an increase in Sn2+ content from the bottom to the top in this heterogeneous FASnI3 film, which generates an additional electric field to prevent the trapping of photo-induced electrons and holes. Consequently, the Sn2+-gradient FASnI3 absorber exhibits a promising efficiency of 13.82% for inverted tin PSCs with an open-circuit voltage increase of 130 mV, and the optimized cell maintains over 13% efficiency after continuous operation under 1-sun illumination for 1,000 h.

Potassium-doped organometal halide perovskite solar cells (PSCs) of more than 20% power conversion efficiency (PCE) without I-V hysteresis were constructed. The crystal lattice of the organometal halide perovskite was expanded with increasing of the potassium ratio, where both absorption and photoluminescence spectra shifted to the longer wavelength, suggesting that the optical band gap decreased. In the case of the perovskite with the 5% K + , the conduction band minimum (CBM) became similar to the CBM level of the TiO 2 -Li. In this situation, the electron transfer barrier at the interface between TiO 2 -Li and the perovskite was minimised. In fact, the transient current rise at the maximum power voltages of PSCs with 5% K + was faster than that without K + . It is concluded that stagnation-less carrier transportation could minimise the I-V hysteresis of PSCs.

Low-cost renewable energies are necessary for the realization of a low-carbon society. Organic photovoltaics such as organic thin-film solar cells 1 , 2 and dye-sensitized solar cells (DSSCs) 3 , 4 are promising candidates for realizing low-cost solar cells. However, device efficiencies are still considerably lower than those of traditional inorganic solar cells. To improve organic photovoltaic performance, approaches are needed to extend the absorption of organic compounds to longer wavelengths. Here, we report efficient DSSCs that exploit near-infrared, spin-forbidden singlet-to-triplet direct transitions in a phosphine-coordinated Ru( II ) sensitizer, DX1. A DSSC using DX1 generated a photocurrent density of 26.8 mA cm −2 , the highest value for an organic photovoltaic reported to date. A tandem-type DSSC employing both DX1 and the traditional sensitizer N719 is shown to have a power conversion efficiency of >12% under 35.5 mW cm −2 simulated sunlight. Single and tandem dye-sensitized solar cells with high power-conversion efficiencies and large photocurrent densities are fabricated using a photosensitizer whose long wavelength absorption originates from a spin-forbidden single–triplet transition.

The effect of TiO 2 interfacial morphology on perovskite crystallinity was investigated by modifying the micro and nanoscale surface roughness of compact TiO 2 . While surface treatments of the compact TiO 2 layer are recognized as effective strategies to enhance the photovoltaic performance of perovskite solar cells, the discussion regarding the crystallinity of perovskite atop TiO 2 has been limited. In this study, we explored the impact of micro and nano scale interface morphology on perovskite crystal formation and its subsequent effects on device performance. Surprisingly, despite the absence of noticeable voids at the interface between the compact TiO 2 and perovskite layers, the perovskite crystal morphology exhibited significant improvement following either micro or nanoscale interfacial modification. This enhancement ultimately led to improved photoconversion efficiency and reduced I–V hysteresis. These results emphasize the importance of underlayer surface morphology in the perovskite crystallization and suggest that the presence of grain boundaries within the perovskite layer may also contribute to I–V hysteresis in perovskite solar cells.

Almost all surfaces sensitive to the ambient environment are covered by water, whereas the impacts of water on surface-dominated colloidal quantum dot (CQD) semiconductor electronics have rarely been explored. Here, strongly hydrogen-bonded water on hydroxylated lead sulfide (PbS) CQD is identified. The water could pilot the thermally induced evolution of surface chemical environment, which significantly influences the nanostructures, carrier dynamics, and trap behaviors in CQD solar cells. The aggravation of surface hydroxylation and water adsorption triggers epitaxial CQD fusion during device fabrication under humid ambient, giving rise to the inter-band traps and deficiency in solar cells. To address this problem, meniscus-guided-coating technique is introduced to achieve dense-packed CQD solids and extrude ambient water, improving device performance and thermal stability. Our works not only elucidate the water involved PbS CQD surface chemistry, but may also achieve a comprehensive understanding of the impact of ambient water on CQD based electronics. Surface of colloidal quantum dot is sensitive to water, and the interaction could potentially alter its chemical environments. Here, Shi et al. investigate how the interaction effects the nanostructures and carrier dynamic in CQDs, and subsequently introduce meniscus-guided coating technique to mitigate CQD fusion triggered by water adsorption.

Photovoltaic generation has stepped up within the last decade from outsider status to one of the important contributors of the ongoing energy transition, with about 1.7% of world electricity provided by solar cells. Progress in materials and production processes has played an important part in this development. Yet, there are many challenges before photovoltaics could provide clean, abundant, and cheap energy. Here, we review this research direction, with a focus on the results obtained within a Japan-French cooperation program, NextPV, working on promising solar cell technologies. The cooperation was focused on efficient photovoltaic devices, such as multijunction, ultrathin, intermediate band, and hot-carrier solar cells, and on printable solar cell materials such as colloidal quantum dots.

The extension of the light absorption of photovoltaics into the near-infrared region is important to increase the energy conversion efficiency. Although the progress of the lead halide perovskite solar cells is remarkable, and high conversion efficiency of >20% has been reached, their absorption limit on the long-wavelength side is ∼800 nm. To further enhance the conversion efficiency of perovskite-based photovoltaics, a hybridized system with near-infrared photovoltaics is a useful approach. Here we report a panchromatic sensitizer, coded DX3, that exhibits a broad response into the near-infrared, up to ∼1100 nm, and a photocurrent density exceeding 30 mA cm −2 in simulated air mass 1.5 standard solar radiation. Using the DX3-based dye-sensitized solar cell in conjunction with a perovskite cell that harvests visible light, the hybridized mesoscopic photovoltaics achieved a conversion efficiency of 21.5% using a system of spectral splitting. Lead halide perovskite solar cells have a limited spectral response in the near infrared. Here, the authors present ruthenium dyes with extended near infrared absorbance and combine perovskite and dye-based solar cells by spectral splitting to obtain broadband, 21.5% efficient solar cells.

Energy harvesting at low light intensities has recently attracted a great deal of attention of perovskite solar cells (PSCs) which are regarded as promising candidate for indoor application. Anomalous hysteresis of the PSCs a complex issue for reliable evaluation of the cell performance. In order to address these challenges, we constructed two new evaluation methods to determinate the power conversion efficiencies ( PCEs ) of PSCs. The first setup is a solar simulator based on light emitting diodes (LEDs) allowing evaluation of the solar cells at wider range of light intensities, ranging from 10 2  to 10 −3  mW·cm −2 . As the overestimate error, we found that the PCEs of dye sensitized solar cell (DSC) and PSCs increase dramatically at low light intensities conditions. Due to the internal capacitance at the interfaces on hybrid solar cells, the measurement of current below 10 −2  mW·cm −2 shows constant value given high PCE , which is related to the capacitive current and origin of the hysteresis. The second setup is a photovoltaic power analyzing system, designed for tracking the maximum power ( P max ) with time. The paper suggests the combination of the LED solar simulator and P max tracking technique as a standard to evaluate the PCE of capacitive solar cells.