SnSe2 Quantum Dots and Chlorhexidine Acetate Suppress Synergistically Non-radiative Recombination Loss for High Efficiency and Stability Perovskite Solar Cells.

Non-radiative recombination losses limit the property of perovskite solar cells (PSCs). Here, a synergistic strategy of SnSe2QDs doping into SnO2 and chlorhexidine acetate (CA) coating on the surface of perovskite is proposed. The introduction of 2D SnSe2QDs reduces the oxygen vacancy defects and increases the carrier mobility of SnO2. The optimized SnO2 as a buried interface obviously improves the crystallization quality of perovskite. The CA containing abundant active sites of ─NH2/─NH─, ─C═N, CO, ─Cl groups passivate the defects on the surface and grain boundary of perovskite. The alkyl chain of CA also improves the hydrophobicity of perovskite. Moreover, the synergism of SnSe2QDs and CA releases the residual stress and regulates the energy level arrangement at the top and bottom interface of perovskite. Benefiting from these advantages, the bulk and interface non-radiative recombination loss is greatly suppressed and thereby increases the carrier transport and extraction in devices. As a result, the best power conversion efficiency (PCE) of 23.41% for rigid PSCs and the best PCE of 21.84% for flexible PSCs are reached. The rigid PSC maintains 89% of initial efficiency after storing nitrogen for 3100 h. The flexible PSCs retain 87% of the initial PCE after 5000 bending cycles at a bending radius of 5 mm.

Buried Interface Optimization for Flexible Perovskite Solar Cells with High Efficiency and Mechanical Stability.

The power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs) are significantly reduced by defect-induced charge non-radiative recombination. Also, unexpected residual strain in perovskite films leads to an unfavorable impact on the stability and efficiency of PSCs, notably flexible PSCs (f-PSCs). Considering these problems, a thorough and effective strategy is proposed by incorporating phytic acid (PA) into SnO2 as an electron transport layer (ETL). With the addition of PA, the Sn inherent dangling bonds are passivated effectively and thus enhance the conductivity and electron mobility of SnO2 ETL. Meanwhile, the crystallization quality of perovskite is increased largely. Therefore, the interface/bulk defects are reduced. Besides, the residual strain of perovskite film is significantly reduced and the energy level alignment at the SnO2 /perovskite interface becomes more matched. As a result, the champion f-PSC obtains a PCE of 21.08% and rigid PSC obtains a PCE of 21.82%, obviously surpassing the PCE of 18.82% and 19.66% of the corresponding control devices. Notably, the optimized f-PSCs exhibit outstanding mechanical durability, after 5000 cycles of bending with a 5 mm bending radius, the SnO2 -PA-based device preserves 80% of the initial PCE, while the SnO2 -based device only remains 49% of the initial value.

Perovskite Crystallization Regulation via Antimonene Quantum Sheets for Highly Efficient and Stable Solar Cells.

The two-step deposition method offers significant advantages in the production of high-performance planar perovskite solar cells (PSCs). Nevertheless, there are still numerous challenges in regulating perovskite crystallization during the two-step process. In this work, two-dimensional (2D) material antimonene quantum sheets (AMQSs) as an additive are introduced to regulate the crystallization process of perovskite. As a result, perovskite films with high crystalline quality and vertical growth orientation are obtained by AMQSs providing heterogeneous nucleation sites with the penetration of a mixture solution of AMQSs and FAI into the PbI2 layer. Also, the influence mechanism of AMQSs on the crystallization of perovskite film is analyzed in details. At the same time, due to the chemical interaction between antimonene and the uncoordinated Pb2+, the defects in the perovskite are efficiently passivated. In addition, the energy level at the perovskite/SnO2 interface becomes more matched, leading to improved charge transport and extraction with the incorporation of AMQSs. Benefiting from the versatile AMQSs, the power conversion efficiency (PCE) of PSCs made by PbI2 + FAI:AMQSs is improved from 20.65 to 22.31% with the vastly enhanced Jsc and Voc. The ambient and operational stability of the unencapsulated PSCs fabricated using the PbI2 + FAI:AMQSs method were significantly improved, retaining 80% of the original PCE after being stored in a dark environment at a relative humidity of 30-40% for 18 days and 83% of the original PCE following continuous AM 1.5G illumination for 200 h.

Regulating the Crystallization Growth of Sn-Pb Mixed Perovskites Using the 2D Perovskite (4-AMP)PbI4 Substrate for High-Efficiency and Stable Solar Cells.

Sn-Pb mixed perovskite solar cells (PSCs) are developing rapidly and making great progress due to their environmentally friendly advantages. High-crystalline quality perovskite films are essential for obtaining high-efficiency and -stability PSCs. Here, the DJ-phase two-dimensional (2D) perovskite (4-AMP)PbI4 (4-AMP is 4-(aminomethyl) piperidine) was used as a substrate to regulate the crystallization growth of the Sn-Pb mixed perovskite for preparing high-quality perovskite films, and the regulation mechanism was analyzed in detail. The results indicate that the suitable amount of the 2D perovskite substrate is favorable for the formation of PbI2/SnI2 films with wide intergranular gaps and vertical distribution grain boundaries. Moreover, the suitable hydrophobicity of the PbI2/SnI2 film made on the 2D perovskite substrate also provides a better template for regulating the formation and dissolution of prophase perovskite capping. In addition, the 4-AMP cations from the collapsed 2D perovskite substrate can diffuse into PbI2/SnI2 films and interact with PbI2 to form the intermediate (4-AMP)-PbI2-(4-AMP) and with SnI2 to form the 2D perovskite (4-AMP)SnI4. All of these promote the diffusion of FAI/MAI molecules and decrease the crystallization growth rate of the Sn-Pb perovskite and thus increase the conversion levels of the perovskite phase and improve the crystallization orientation and quality of the perovskite, which helps mitigate the erosion of water and oxygen. In addition, the 2D perovskite used as a substrate can passivate the buried interface defects and improve the interfacial contact. Moreover, the diffusion behavior of 4-AMP cations regulates the perovskite energy levels, which match more with those of the electron transport layer. As a result, the champion device made on the (4-AMP)PbI4 substrate acquires a power conversion efficiency (PCE) of 17.7% with an open-circuit voltage (Voc) of 0.806 V, a short-circuit current density (Jsc) of 28.97 mA cm-2, and a fill factor (FF) of 75.86%, far exceeding those of the control device. Meanwhile, the unencapsulated PSCs modified with 4-AH retain above 70% of the initial efficiency value after storage for 1200 h in N2 at room temperature and about 25% of its initial efficiency after exposure to air for nearly 300 h with RH = 30 ± 10% at room temperature, while the control device has only 30% of the initial efficiency and near-zero efficiency at the same conditions.

Multifunction Sandwich Structure Based on Diffusible 2-Chloroethylamine for High-Efficiency and Stable Tin-Lead Mixed Perovskite Solar Cells.

Low-bandgap tin-lead mixed perovskites (PVKs) are necessary for all-perovskite tandem solar cells. This work proposes a multifunctional sandwich structure with 2-chloroethylamine (CEA) as the top and bottom interface layer and perovskite as the core layer. The sandwich structured CEA allows large ClCH2CH2NH3+ and small Cl- to diffuse into the crystal lattice and grain boundaries of perovskites, endowing an excellent antioxidation property by forming Sn(0), coordinating with SnI2, and controlling the perovskite crystallization process. Moreover, the energy level alignment at the interface of the perovskite and transport layer becomes more matched. As a result, the CEA-modified champion device acquires a power conversion efficiency of 18.13% with an open-circuit voltage of 0.82 V and a short-circuit current density of 30.06 mA cm-2. Meanwhile, the environmental stability of CEA-modified devices is substantially enhanced. This work introduces a new strategy for improving the performance and stability of tin-lead mixed perovskite solar cells.

2D Perovsktie Substrate-Assisted CsPbI3 Film Growth for High-Efficiency Solar Cells.

High-quality perovskite films are beneficial for fabricating perovskite solar cells (PSCs) with excellent photoelectric performance. The substrate on which the perovskite film grows plays a profound role in improving the crystallization quality of the perovskite film. Here, we proposed a novel method for optimizing CsPbI3 perovskite films, that is, two-dimensional (2D) perovskite substrate-assisted growth (2D-PSAG) method. The prepared PEA2PbI4 2D perovskite with proper wettability and roughness is used as a substrate to fabricate the high-quality CsPbI3 film. Moreover, it is found that PEA cations show a vertical gradient distribution within the whole CsPbI3 film because of their bottom-up self-diffusion. Also, PEA cations induce the moderate distortion of [PbI6]4- octahedron and slight lattice contraction of CsPbI3 by chemically bonding between Pb and N atoms. Surprisingly, the trace amounts of PEA cations lead to a bottom-up gradient phase transition from γ-CsPbI3 to ß-CsPbI3. Therefore, the energy-level alignment becomes more matched at the interface of the perovskite layer/hole transport layer (poly3-hexylthiophene, P3HT), which denotes a large improvement of hole transport and extraction in PSCs made with the 2D-PSAG method. As a result, the CsPbI3-based PSCs with P3HT as a hole transport layer exhibit a champion efficiency of 17.13%, while the control device exhibits a PCE of only 14.16%. The PSCs made by the 2D-PSAG method retain above 70% of the initial PCE value after storage of 9 days in air (RH 10-20%), while the control device decomposes completely after 9 days. The improved stability could originate from the steric effects of PEA cations and the high crystallization quality of the mixed-phase CsPbI3 film. Therefore, 2D-PSAG is a novel and promising strategy to develop all-inorganic PSCs with high performance and stability.

Biocompatible semiconducting polymer nanoparticles as robust photoacoustic and photothermal agents revealing the effects of chemical structure on high photothermal conversion efficiency.

Understanding the relationship between polymer chemical structure and its performance of photoacoustic imaging (PAI) and photothermal therapy (PTT) is important for developing ideal PAI/PTT agents. In this report, four semiconducting polymer nanoparticles (SPNs) with different donor-acceptor architectures are self-assembled for highly effective PAI-guided PTT. In particular, SPN1 with the longest π-conjugation length and the highest mass extinction coefficient which are beneficial for intramolecular charge transfer as well as light harvesting, exhibits the highest photothermal conversion efficiency up to 52.6%. Moreover, the as-prepared SPN1 possess good water-dispersibility, robust size-stability and excellent photothermal properties. Furthermore, the SPN1 not only exhibits a remarkable cancer cell-killing ability but also shows a prominent tumor inhibition capacity. Finally, the as-prepared water-dispersible SPN1 displays good biocompatibility and biosafety, making it a promising candidate for future biomedical applications. Considering the plenty of near-infrared absorbing semiconducting polymer available, our work provides fundamental insights for rational design and preparation of highly efficient SPN-based PAI/PTT agents for cancer theranostics.