No abstract

An efficient electron transport layer (ETL) plays a key role in promoting carrier separation and electron extraction in planar perovskite solar cells (PSCs). An effective composite ETL is fabricated using carboxylic‐acid‐ and hydroxyl‐rich red‐carbon quantum dots (RCQs) to dope low‐temperature solution‐processed SnO2, which dramatically increases its electron mobility by ≈20 times from 9.32 × 10−4 to 1.73 × 10−2 cm2 V−1 s−1. The mobility achieved is one of the highest reported electron mobilities for modified SnO2. Fabricated planar PSCs based on this novel SnO2 ETL demonstrate an outstanding improvement in efficiency from 19.15% for PSCs without RCQs up to 22.77% and have enhanced long‐term stability against humidity, preserving over 95% of the initial efficiency after 1000 h under 40–60% humidity at 25 °C. These significant achievements are solely attributed to the excellent electron mobility of the novel ETL, which is also proven to help the passivation of traps/defects at the ETL/perovskite interface and to promote the formation of highly crystallized perovskite, with an enhanced phase purity and uniformity over a large area. These results demonstrate that inexpensive RCQs are simple but excellent additives for producing efficient ETLs in stable high‐performance PSCs as well as other perovskite‐based optoelectronics.

2D Ruddlesden−Popper (2DRP) tin (Sn) perovskite solar cells (PSCs) play an irreplaceable role in advancing the commercialization of perovskite-based photovoltaic devices due to their low toxicity and improved stability. However, the efficiency of 2DRP Sn PSCs has not made a breakthrough owing to incompletely oriented crystal growth and poor film morphology, which is limited by a complex and uncontrollable crystallization process. Here, we first introduce the mixed spacer organic cations [n-butylamine (BA) and phenylethylamine (PEA)] in 2DRP Sn perovskite to control the crystallization process. We find that when the BA + and PEA + cowork to form [(BA 0.5 PEA 0.5 ) 2 FA 3 Sn 4 I 13 ] 2DRP perovskites, the intermediate phase impeding the homogeneous and ordered nucleation of the crystal is suppressed effectively, thus enabling a high-quality film morphology and improved crystal orientation. Benefitting from it, the power conversion efficiency (PCE) is improved to 8.82%, which is the highest one among the 2DRP Sn PSCs as far as we known.

Solution-processed metal-halide perovskites have demonstrated immense potential in photovoltaic applications. Inkjet printing is a facile scalable approach to fabricate large-area perovskite solar cells (PSCs) due to its costeffectiveness and near unity material utilization ratio. However, controlling crystallinity of the perovskite during the inkjet printing remains a challenge. The PSCs deposited by inkjet printing typically have much lower power conversion efficiencies (PCEs) than those by spin-coating. Here, we show that high-quality perovskite films could be inkjet-printed with an innovative vacuum-assisted thermal annealing post-treatment and optimized solvent composition. High-performance PSCs based on printed CH 3 NH 3 PbI 3 with a PCE of 17.04% for 0.04 cm 2 (13.27% for 4.0 cm 2 ) and negligible hysteresis (lower than 1.0%) are demonstrated. These efficiencies are much higher than the previously reported ones using inkjet-printing ( 12.3% for 0.04 cm 2 ). The inkjet printing combined with vacuum-assisted thermal annealing could be an effective low-cost approach to fabricate high-performance perovskite optoelectronic thin film devices (including solar cells, lasers, photodetectors, and light-emitting diodes) with high-volume production.Metal-halide perovskites possess extraordinary photovoltaic desired features, including high charge carrier mobilities, [1][2][3] low exciton binding energies, [4][5] long charge carrier diffusion lengths, [6] broad light absorption spectra, large absorption coefficient, [7,8] and low-cost solution processability. [9] Therefore, the metal-halide perovskites have been considered as a new type promising light harvesting materials for the third generation photovoltaic applications. Notably, the power conversion efficiency (PCE) of the perovskite solar cell (PSC) has boosted from 3.8% to the certified 22.7% within the past 8 years and approached the performance of representative traditional solar cells based on crystallized silicon, cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). PSCs have demonstrated unbelievable developing speed and a bright prospect in photovoltaics. [10][11] However, most of the perovskite layers studied so far are deposited via the nonscalable spin-coating method with low material utilization ratio, [12][13][14] which hinders the commercialization of PSCs. To fabricate large-area and uniform perovskite films, a variety of film deposition technologies, including vapor assisted deposition, [15][16][17] spray-deposition, [18] soft-cover deposition, [19] brushpainting, [20] blade-coating, [21][22][23] slot-die coating, [24][25][26] and inkjet printing, [27][28][29][30][31][32][33] have been explored. Among these techniques, inkjet printing has been considered as a facile scalable approach to fabricate large-area PSCs for its cost-effectiveness, high writing accuracy, and near unity material utilization ratio. [34][35][36] Up to now, perovskite films have been inkjet printed with onestep method (e.g., print CH 3 NH 3 PbI 3 (MAPbI 3 ) pre...

CF3PEAI, an amphipathic passivation agent, can passivate multiple perovskite defects leading to high performance and stability of perovskite solar cells.

stability, [3,4] insensitivity to moisture and ultralow self-doping effect. [5][6][7][8] Unlike the more roundly expanded 3D perovskites, LDRP perovskites with chemical formula of (A) 2 MA n−1 Pb n I 3n+1 (where A is alkylammonium cation and n is the number of inorganic slabs) are considered as infinite nanoplatelets with atomic or molecular size obtained by quantizing the number of [PbI 6 ] 4− octahedra layers between organic ligands which causes quantum and dielectric confinement along one axis. [9][10][11][12] These ultrathin perovskite nanoplatelets are assembled together by intercalating organic cations (Van der Waals force), which protects the degradation of lattice by water and oxygen, resists ion migration and maintains the structural integrity of the 2D and quasi-2D (q-2D) perovskites. [13][14][15] As a result, perovskite solar cells (PSCs) prepared by LDRP perovskite exhibit good stability. [16][17][18][19][20] Although hydrophobic slabs of LDRP perovskites prevent corrosion form water and oxygen, the power conversion efficiency (PCE) of the PSCs are much lower than that of 3D perovskite devices. As the high dielectric constant and exciton binding energy of LDRP perovskite not only narrow the optical absorption windows, but also confine electron-hole pairs to form tight bound excitons. [21][22][23] Low-dimensional Ruddlesden-Popper (LDRP) perovskites are a current theme in solar energy research as researchers attempt to fabricate stable photovoltaic devices from them. However, poor exciton dissociation and insufficiently fast charge transfer slows the charge extraction in these devices, resulting in inferior performance. 1,4-Butanediamine (BEA)-based low-dimensional perovskites are designed to improve the carrier extraction efficiency in such devices. Structural characterization using single-crystal X-ray diffraction reveals that these layered perovskites are formed by the alternating ordering of diammonium (BEA 2+ ) and monoammonium (MA + ) cations in the interlayer space (B-ACI) with the formula (BEA) 0.5 MA n Pb n I 3n+1 . Compared to the typical LDRP counterparts, these B-ACI perovskites deliver a wider light absorption window and lower exciton binding energies with a more stable layered perovskite structure. Additionally, ultrafast transient absorption indicates that B-ACI perovskites exhibit a narrow distribution of quantum well widths, leading to a barrier-free and balanced carrier transport pathway with enhanced carrier diffusion (electron and hole) length over 350 nm. A perovskite solar cell incorporating BEA ligands achieves record efficiencies of 14.86% for (BEA) 0.5 MA 3 Pb 3 I 10 and 17.39% for (BEA) 0.5 Cs 0.15 (FA 0.83 MA 0.17 ) 2.85 Pb 3 (I 0.83 Br 0.17 ) 10 without hysteresis. Furthermore, the triple cations B-ACI devices can retain over 90% of their initial power conversion efficiency when stored under ambient atmospheric conditions for 2400 h and show no significant degradation under constant illumination for over 500 h.

Environment-friendly protic amine carboxylic acid ionic liquids (ILs) as solvents is a significant breakthrough with respect to traditional highly coordinating and toxic solvents in achieving efficient and stable perovskite solar cells (PSCs) with a simple one-step air processing and without an antisolvent treatment approach. However, it remains mysterious for the improved efficiency and stability of PSCs without any passivation strategy. Here, we unambiguously demonstrate that the three functions of solvents, additive, and passivation are present for protic amine carboxylic acid ILs. We found that the ILs have the capability to dissolve a series of perovskite precursors, induce oriented crystallization, and chemically passivate the grain boundaries. This is attributed to the unique molecular structure of ILs with carbonyl and amine groups, allowing for strong interaction with perovskite precursors by forming C=O…Pb chelate bonds and N-H…I hydrogen bonds in both solution and film. This finding is generic in nature with extension to a wide range of IL-based perovskite optoelectronics.

Organic solid materials with color-tunable emissions have been extensively applied in various fields. However, a rational design and facile synthesis of an ideal fluorophore are still challenging due to the undesirable aggregation-caused quenching effect in concentrated solution and solid form. Herein, we have developed a series of 2-(2′-hydroxyphenyl)­benzothiazole (HBT)-derived color-tunable solid emitters by switching functional groups at the ortho-position of a hydroxyl group via formylation and an aldol condensation reaction. By tuning the electron-withdrawing ability and the π-conjugated framework introduced by the functional groups, fluorophores emit light covering the full-color range from blue to near-infrared regions with high quantum yields in their solid form and show a significant solvatochromic effect in polar solvents. The aggregation-induced emission (AIE) or aggregation-induced emission enhancement (AIEE) and excited-state intramolecular proton transfer (ESIPT) involving fluorescence mechanism, along with their inter/intramolecular interactions in crystals, are elucidated to depict the key factors for tunable emissions and high emitting efficiency. Furthermore, high-quality white-light-emitting materials are obtained in various solvents and polydimethylsiloxane (PDMS) films with combined fluorophores. Overall, these studies report a promising strategy for the construction of organic solid materials with color-tunable emission and shed light on methods for obtaining desirable emission efficiency.