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Modification of the charge transport layers is an effective way to improve charge transport and performance of perovskite solar cells (PSCs). The ions in the ionic compounds used for the modification of SnO

Drop-casting was used to make MAPbI 3 films for solar cells. The crystal growth in drop-cast MAPbI 3 f ilms was regulated by adjusting temperature. A mechanism for the formation of different morphology was proposed by combining in-situ crystal-growth study with XRD measurements. The crystals in the films made at low temperature (60 °C) and high temperature (≥120 °C) are (110) and (200) oriented, respectively. The different crystal growth mode leads to quite different film morphology. Compared with spin-coating, drop-casting shows much better tolerance to humidity. MAPbI 3 solar cells made under 88% humidity delivered a PCE of 18.17%, which is the highest PCE for perovskite solar cells made under >70% humidity without antisolvent assistance.

The power conversion efficiency for single-junction solar cells is limited by the Shockley-Quiesser limit. An effective approach to realize high efficiency is to develop multi-junction cells. These years have witnessed the rapid development of organic–inorganic perovskite solar cells. The excellent optoelectronic properties and tunable bandgaps of perovskite materials make them potential candidates for developing tandem solar cells, by combining with silicon, Cu(In,Ga)Se2 and organic solar cells. In this review, we present the recent progress of perovskite-based tandem solar cells, including perovskite/silicon, perovskite/perovskite, perovskite/Cu(In,Ga)Se2, and perovskite/organic cells. Finally, the challenges and opportunities for perovskite-based tandem solar cells are discussed.

The excellent performance and stability of perovskite solar cells (PSCs) based on quasi-2D Ruddlesden–Popper perovskites (RPPs) holds promise for their commercialization. Further improvement in the performance of 2D PSCs requires a detailed understanding of the microstructure of the quasi-2D perovskite films. Based on scanning transmission electron microscopy (STEM), time-resolved photoluminescence, and transient absorption measurements, a new sandwich-like structural model is proposed to describe the phase distribution of RPPs. In contrast to the conventional gradient distribution, it is found that small-n RPPs are sandwiched between large-n RPP phase layers at the front and back sides owing to crystallization initiated from both interfaces during film formation. This sandwich-like distribution profile facilitates excitons funneling from the film interior to both surfaces for dissociation while free carriers transport via large-n channels that permeate the film to ensure efficient charge collection by the corresponding electrodes, which is favorable for high-performance photovoltaics. This discovery provides a new fundamental understanding of the operating principles of 2D PSCs and has valuable implications for the design and optimization strategies of optoelectronic devices based on quasi-2D RPPs films.

Introducing layered quasi-2D perovskite phases into a conventional 3D perovskite light-absorbing matrix is a promising strategy for overcoming the limited environmental stability of 3D perovskite solar cells. Here, we present a simple drop-casting method for preparing hybrid perovskite films comprising both quasi-2D and quasi-3D phases, formed using phenylethylammonium or iso-butylammonium as spacer cations. The film morphology, phase purity, and crystal orientation of the hybrid quasi-2D/3D perovskite films are improved significantly by applying a simple N2 blow-drying step, together with inclusion of methylammonium chloride as an additive. An enhanced power conversion efficiency of 16.0% is achieved using an iso-butylammonium-based quasi-2D/3D perovskite layer which, to our knowledge, is the highest recorded to date for a quasi-2D/3D perovskite solar cells containing a non-spin-cast perovskite layer prepared under ambient laboratory conditions. Perovskite solar cells have substantial potential for solar conversion, but developing simple and scalable fabrication processes is challenging. Here, a drop-casting process compatible with roll-to-roll production of quasi-2D/3D perovskite layers is developed, with a conversion efficiency of up to 16%.

Layered perovskite films, composed of two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs), show improved stability compared to their conventional three-dimensional (3D) counterparts in perovskite solar cells (PSCs). However, 2D PSCs exhibit a lower power conversion efficiency (PCE), which has been attributed to compositional inhomogeneity and nonuniform alignment of the 2D perovskite phases. Methylammonium chloride (MACl) has been adopted as an additive to improve the PCE and the operational stability of 2D PSCs, although the role of MACl in performance enhancement is unclear. In this work, time- and spatially resolved fluorescence and absorption techniques have been applied to study the composition and charge carrier dynamics in MACl-doped BA2MA4Pb5I16 (⟨n⟩ = 5) layered perovskite films. The inhomogeneous phase orientation distribution in the direction orthogonal to the substrate for undoped layered perovskite films undergoes reorganization upon MACl doping. Based on structural and crystallographic analyses, it is revealed that MACl can facilitate the crystallization of small-n 2D perovskite phases at the cost of consuming an increased amount of BA cations. Consequently, an increase in the thickness of large-n 2D perovskite phases accompanies their enhanced perpendicular alignment ([101] crystalline orientation) to the substrate, which facilitates charge carrier transport and collection by electrodes. The defect passivation of the MACl-doped layered perovskite film provided by the small-n phase is also beneficial to the photovoltaic performance of the PSC device. A maximum PCE (∼14.3%) was achieved at 6 mol % MACl doping, with this optimum level influenced by the increased interfacial roughness of the layered perovskite film caused by the edges of small-n perovskite flakes emerging on the front surface.

Organic solar cells have attracted academic and industrial interests due to the advantages like lightweight, flexibility and roll-to-roll fabrication. Nowadays, 18% power conversion efficiency has been achieved in the state-of-the-art organic solar cells. The recent rapid progress in organic solar cells relies on the continuously emerging new materials, device fabrication technologies, and the deep understanding on film morphology, molecular packing and device physics. Donor and acceptor materials are the key materials for organic solar cells since they determine the device performance. The past 25 years have witnessed an odyssey in developing high-performance donors and acceptors. In this review, we focus on those star materials and milestone work, and introduce the molecular structure evolution of the key materials. These key materials include homopolymer donors, D-A copolymer donors, A-D-A small molecule donors, fullerene acceptors and nonfullerene acceptors. At last, we outlook the challenges and very important directions in key materials development.

The intrinsic phase instability of CsPbI2Br perovskite hinders its development and application in solar cells. Herein, we adopt 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF6), a hydrophobic ionic liquid (IL), to improve the phase stability of CsPbI2Br. Density functional theory calculation reveals that the formation energy of CsPbI2Br with BMIMPF6 is reduced, thereby restraining the [PbX6]4− octahedral tilting. The reduced structural distortion and relaxed lattice strain result in improved phase stability of CsPbI2Br. In addition, the interfacial dipole moment increases after introducing BMIMPF6, which facilitates the charge transfer. Consequently, the CsPbI2Br solar cells with BMIMPF6 deliver a power conversion efficiency (PCE) of 16.2% along with excellent stability. The unencapsulated devices with BMIMPF6 maintain 98.9%, 88.6%, and 99.5% of the initial PCEs after 1200 h storage in N2, 1000 h storage in air (30% relative humidity), and 200 thermal cycles (25–100°C), respectively.

Perovskite solar cells (PSCs) have attracted tremendous attention as a promising alternative candidate for clean energy generation. Many attempts have been made with various deposition techniques to scale-up manufacturing. Slot-die coating is a robust and facile deposition technique that can be applied in large-area roll-to-roll (R2R) fabrication of thin film solar cells with the advantages of high material utilization, low cost and high throughput. Herein, we demonstrate the encouraging result of PSCs prepared by slot-die coating under ambient environment using a two-step sequential process whereby PbI

Small-area metal-halide perovskite solar cells (PSCs) having power-conversion efficiencies (PCEs) of greater than 25% can be prepared by using a spin-coated perovskite layer, but this technique is not readily transferrable to large-scale manufacturing. Drop-casting is a simple alternative method for film formation that is more closely aligned to industry-relevant coating processes. In the present work, drop-casting was used to prepare films for screening two-dimensional Ruddlesden-Popper (2DRP) metal-halide perovskite formulations for potential utility in PSCs, without additional processing steps such as inert-gas blowing or application of antisolvent. The composition of the 2DRP formulation used for drop-casting was found to have a profound effect on optical, spectroscopic, morphological, and phase-distribution properties of the films as well as the photovoltaic performance of related PSC devices. This facile method for screening film quality greatly assists in speeding up the identification of perovskite formulations of interest. The optimal 2DRP perovskite formulation identified from screening was utilized for industry-relevant one-step roll-to-roll slot-die coating on a flexible plastic substrate, producing PSCs having PCEs of up to 8.8%. A mechanism describing film formation and phase distribution in the films is also proposed.

Owing to its nice performance, low cost, and simple solution-processing, organic-inorganic hybrid perovskite solar cell (PSC) becomes a promising candidate for next-generation high-efficiency solar cells. The power conversion efficiency (PCE) has boosted from 3.8% to 25.2% over the past ten years. Despite the rapid progress in PCE, the device stability is a key issue that impedes the commercialization of PSCs. Recently, all-inorganic cesium lead halide perovskites have attracted much attention due to their better stability compared with their organic-inorganic counterpart. In this progress report, we summarize the properties of CsPb(IxBr1−x)3 and their applications in solar cells. The current challenges and corresponding solutions are discussed. Finally, we share our perspectives on CsPb(IxBr1−x)3 solar cells and outline possible directions to further improve the device performance.

A wide-bandgap copolymer donor PPN4T-2F based on a phenanthridin-6(5H)-one unit was developed. PPN4T-2F has a large optical bandgap of 2.15 eV and a deep highest occupied molecular orbital level of −5.43 eV. Solar cells based on PPN4T-2F and a nonfullerene acceptor, IT-4F, afforded a power conversion efficiency (PCE) of 8.54%. PPN4T-2F is comparable to the efficient ultra-wide-bandgap copolymer donors.

State-of-the-art photodetectors which apply hybrid perovskite materials have emerged as powerful candidates for next-generation light sensing. Among them, lead-based ones are the most popular beyond doubt on account of their unique and superior optoelectronic properties. Nevertheless, trade-off toward commercialization exists between nontoxicity and high performance, with the poor stability of lead-based perovskites, indicating that it is indispensable to substitute lead with nontoxic element meanwhile bringing about a comparable figure of merit of photodetectors and relatively long-term stability. Herein, recent advances in lead-free perovskite photodetectors are reviewed, analyzing the principle while designing new materials and highlighting some remarkable progress, which are comparable, even superior, to lead-based photodetectors. Furthermore, their potential strategy in optical communication, image sensing, narrowband photodetection, etc., is examined and a perspective on developing new materials and photodetectors with superior properties for more practical applications is provided.

How to deliver chemotherapeutic drugs efficiently and selectively to tumor cells to improve therapeutic efficacy remains a difficult problem. We herein construct an efficient cell-targeting drug delivery system (Sgc8-MSN/Dox) based on aptamer-modified mesoporous silica nanoparticles that relies on the tumor-targeting ability of the aptamer Sgc8 to deliver doxorubicin (Dox) to leukemia cells in a targeted way, thereby improving therapeutic efficacy and reducing toxicity. In this work, Sgc8-MSN/Dox showed sustained Dox release, and they targeted and efficiently killed CCRF-CEM human acute T lymphocyte leukemia cells, suggesting potential as a cancer therapy.

Phenyl-C61-butyric acid methyl ester (PCBM) is universally used as the electron-transport layer (ETL) in the low-cost inverted planar structure of perovskite solar cells (PeSCs). PCBM brings tremendous challenges in upscaling of PeSCs using industry-relevant methods due to its aggregation behavior, which undermines the power conversion efficiency and stability. Herein, we highlight these, seldom reported, challenges with PCBM. Furthermore, we investigate the potential of nonfullerene indacenodithiophene (IDT)-based molecules by employing a commercially available variant, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3- d:2',3'- d']- s-indaceno[1,2- b:5,6- b'] dithiophene (ITIC), as a PCBM replacement in ambient-processed PeSCs. Films fabrication by laboratory-based spin-coating and industry-relevant slot-die coating methods are compared. Although similar power-conversion efficiencies are achieved with both types of ETL in a simple device structure fabricated by spin-coating, the nanofibriller morphology of ITIC compared to the aggregated morphology of PCBM films enables improved mechanical integrity and stability of ITIC devices. Upon slot-die coating, the aggregation of PCBM is exacerbated, leading to significantly lower power-conversion efficiency of devices than spin-coated PCBM as well as slot-die-coated ITIC devices. Our results clearly indicate that IDT-based molecules have great potential as an ETL in PeSCs, offering superior properties and upscaling compatibility than PCBM. Thus, we present a short summary of recently emerged nonfullerene IDT-based molecules from the field of organic solar cells and discuss their scope in PeSCs as electron or hole-transport layer.

The rapid improvement in power conversion efficiencies (PCE) to record high levels have highlighted perovskite solar cells’ great potential to be commercialized in the near future. Continuous roll-to-roll (R2R) processing on flexible substrates enables ultra low-cost and high throughput manufacturing, which is essential for perovskite solar cells to make a breakthrough in cost per Watt compared to commercially established solar cells technologies. Here we demonstrate a facile spin-coating-free and R2R compatible blowing-assisted drop-casting (BADC) method to prepare CH3NH3PbI3 films for perovskite solar cells. The crystallinity and morphology of CH3NH3PbI3 films and device performance are significantly improved by optimization of the formulation with an NH4Cl additive. The perovskite solar cell prepared in air with a maximum PCE of 19.48% is obtained using modified poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (m-PEDOT:PSS) as the hole transport layer (HTL). The cells based on the structure of ITO/m-PEDOT:PSS/CH3NH3PbI3/PCBM/Ca/Al exhibit negligible current hysteresis. The optimized formulation is then successfully applied to slot-die coating on glass and subsequently to R2R on a flexible substrate, giving record PCEs of 15.57% and 11.16%, respectively.

The present study aimed to isolate and characterize side population (SP) cells in the human lung cancer A549 cell line, and elucidate the molecular mechanism of SP cells underlying lung cancer. The SP and non-SP (NSP) cells in A549 cells were isolated and their differentiation was analyzed by fluorescence-activated cell sorting. An in vitro plate clone assay, Matrigel® Transwell assay and chemoresistance analysis of the sorted SP and NSP cells were performed. In addition, the sorted SP and NSP cells were injected into BALB/c nude mice to detect their tumorigenic potential in vivo. The expression of ATP-binding cassette sub-family G member 2 (ABCG2) in transplanted tumors was detected by immunohistochemistry. The SP and NSP cells were successfully isolated. The results demonstrated that SP cells accounted for 1.09% of live A549 cells. SP cells produced SP and NSP cells, while NSP cells only produced NSP cells. In addition, SP cells formed more colonies, exhibited improved invasive ability and increased levels of chemoresistance compared with NSP cells in vitro. SP cells demonstrated a higher tumorigenic potential in BALB/c nude mice, and the number of ABCG2-positive cells in the SP xenograft tumors were significantly increased compared with that in the NSP xenograft tumors. The present study indicated that SP cells isolated from the human lung cancer A549 cell line demonstrated increased tumorigenicity, and improved invasive ability and chemoresistance compared with NSP cells. In addition, detection of ABCG2 expression may assist in predicting the chemotherapeutic outcome of patients, and serve as a target for treating lung cancer.

A facile two-step drop-coating method was used to make FA0.88MA0.12PbIxBr3−x (0 ≤x ≤ 3) perovskite films for the first time. The films formed via a self-spreading process, without the assistance of coating apparatuses, gas blowing, vacuum, or antisolvent. High-quality perovskite films with different bandgaps were made and the photovoltaic performance was investigated. The cells with FA0.88MA0.12PbI2.85Br0.15 offered a champion PCE of 21.08%, which is higher than the PCEs for perovskite solar cells made by other two-step non-spin-coating methods. The FA0.88MA0.12PbBr3 cells gave a champion PCE of 10.86%, which is the highest PCE for FAxMA1−xPbBr3 cells. The drop-coating method enables making perovskite solar cells without complex equipment. “Fully handmade” perovskite solar cells with drop-coated SnO2, drop-coated perovskite, and painted carbon electrode were made in air, giving a PCE of 14.04%.

Here we demonstrate a room-temperature drop-coating method for MAPbI3 films. By using low-boiling-point solvent, high-quality MAPbI3 films were made by simply casting a drop of solution onto the substrate at room temperature. This approach took advantage of the synergistic effect of good wettability and volatility of the solvent, enabling high nuclei density and compact film at room temperature. The crystal growth in different solvents was in-situ observed by using optical microscope, which helped us to understand the mechanism for the formation of different film morphology. Perovskite solar cells gave a PCE of 18.21%.

Flexible perovskite solar cells (f-PSCs) have been attracting tremendous attention due to their potentially commercial prospects in flexible energy system and mobile energy system. Reducing the energy barriers and charge extraction losses at the interfaces between perovskite and charge transport layers is essential to improve both efficiency and stability of f-PSCs. Herein, 4-trifluoromethylphenylethylamine iodide (CF3 PEAI) is introduced to form a 2D perovskite at the interface between perovskite and hole transport layer (HTL). It is found that the 2D perovskite plays a dual-functional role in aligning energy band between perovskite and HTL and passivating the traps in the 3D perovskite, thus reducing energy loss and charge carrier recombination at the interface, facilitating the hole transfer from perovskite to the Spiro-OMeTAD. Consequently, the photovoltaic performance of f-PSCs is significantly improved, leading to a power conversion efficiency (PCE) of 21.1% and a certified PCE of 20.5%. Furthermore, the long-term stability of f-PSCs is greatly improved through the protection of 2D perovskite layer to the underlying 3D perovskite. This work provides an excellent strategy to produce efficient and stable f-PSCs, which will accelerate their potential applications.

A family of perovskite light absorbers (NH4)3Sb2IxBr9−x (0≤x≤9) was prepared. These materials show good solubility in ethanol, a low-cost, hypotoxic, and environmentally friendly solvent. The light absorption of (NH4)3Sb2IxBr9−x films can be tuned by adjusting I and Br content. The absorption onset for (NH4)3Sb2IxBr9−x films changes from 558 nm to 453 nm as x changes from 9 to 0. (NH4)3Sb2I9 single crystals were prepared, exhibiting a hole mobility of 4.8 cm2 V−1 s−1 and an electron mobility of 12.3 cm2 V−1 s−1. (NH4)3Sb2I9 solar cells gave an open-circuit voltage of 1.03 V and a power conversion efficiency of 0.51 %.

A family of perovskite light absorbers (NH4 )3 Sb2 Ix Br9-x (0≤x≤9) was prepared. These materials show good solubility in ethanol, a low-cost, hypotoxic, and environmentally friendly solvent. The light absorption of (NH4 )3 Sb2 Ix Br9-x films can be tuned by adjusting I and Br content. The absorption onset for (NH4 )3 Sb2 Ix Br9-x films changes from 558 nm to 453 nm as x changes from 9 to 0. (NH4 )3 Sb2 I9 single crystals were prepared, exhibiting a hole mobility of 4.8 cm2 V-1 s-1 and an electron mobility of 12.3 cm2 V-1 s-1 . (NH4 )3 Sb2 I9 solar cells gave an open-circuit voltage of 1.03 V and a power conversion efficiency of 0.51 %.

Two donor-acceptor (D-A) polymers PTTBDTP and PBTBDTP were developed by copolymerizing lactam acceptor [7,7′-bidithieno[3,2-b:2′,3′-d]pyridine]-5,5′(4H,4′H)-dione (BDTP) with thieno[3,2-b]thiophene (TT) or 2,2′-bithiophene (BT) in good yields. PTTBDTP and PBTBDTP exhibited excellent thermal stability and low HOMO energy levels of −5.52 eV ∼ −5.54 eV. Compared with PTTBDTP, PBTBDTP possessed broader absorption spectra, better crystallinity, and higher hole mobility. Therefore inverted polymer solar cells based on PBTBDTP:PC71BM achieved a higher PCE of 6.86%, with an open-circuit voltage (Voc) of 0.87 V, a short-circuit current (Jsc) of 10.97 mA/cm2 and a fill factor (FF) of 71.85%. Meanwhile, PTTBDTP:PC71BM solar cells gave a PCE of 5.84%. These results have demonstrated that lactam BDTP is a good building block for PSC applications.

The influence of precursor solution properties, fabrication environment, and antisolvent properties on the microstructural evolution of perovskite films is reported. First, the impact of fabrication environment on the morphology of methyl ammonium lead iodide (MAPbI3 ) perovskite films with various Lewis-base additives is reported. Second, the influence of antisolvent properties on perovskite film microstructure is investigated using antisolvents ranging from nonpolar heptane to highly polar water. This study shows an ambient environment that accelerates crystal growth at the expense of nucleation and introduces anisotropies in crystal morphology. The use of antisolvents enhances nucleation but also influences ambient moisture interaction with the precursor solution, resulting in different crystal morphology (shape, size, dispersity) in different antisolvents. Crystal morphology, in turn, dictates film quality. A homogenous spherulitic crystallization results in pinhole-free films with similar microstructure irrespective of processing environment. This study further demonstrates propyl acetate, an environmentally benign antisolvent, which can induce spherulitic crystallization under ambient environment (52% relative humidity, 25 °C). With this, planar perovskite solar cells with ≈17.78% stabilized power conversion efficiency are achieved. Finally, a simple precipitation test and in situ crystallization imaging under an optical microscope that can enable a facile a priori screening of antisolvents is shown.