Sn-Based Perovskite Solar Cells towards High Stability and Performance.

Recent years have witnessed rapid development in the field of tin-based perovskite solar cells (TPSCs) due to their environmental friendliness and tremendous potential in the photovoltaic field. Most of the high-performance PSCs are based on lead as the light-absorber material. However, the toxicity of lead and the commercialization raise concerns about potential health and environmental hazards. TPSCs can maintain all the optoelectronic properties of lead PSCs, as well as feature a favorable smaller bandgap. However, TPSCs tend to undergo rapid oxidation, crystallization, and charge recombination, which make it difficult to unlock the full potential of such perovskites. Here, we shed light on the most critical features and mechanisms affecting the growth, oxidation, crystallization, morphology, energy levels, stability, and performance of TPSCs. We also investigate the recent strategies, such as interfaces and bulk additives, built-in electric field, and alternative charge transport materials that are used to enhance the performance of the TPSCs. More importantly, we have summarized most of the recent best-performing lead-free and lead-mixed TPSCs. This review aims to help future research in TPSCs to produce highly stable and efficient solar cells.

Anticancer Activity of Thiophene Carboxamide Derivatives as CA-4 Biomimetics: Synthesis, Biological Potency, 3D Spheroid Model, and Molecular Dynamics Simulation.

The present study aimed to synthesize thiophene carboxamide derivatives, which are considered biomimetics of the anticancer medication Combretastatin A-4 (CA-4), and compare the similarity in the polar surface area (PSA) between the novel series and CA-4. Our results showed that the PSA of the most synthesized structures was biomimetic to CA-4, and similar chemical and biological properties were observed against Hep3B cancer cell line. Among the synthesized series 2b and 2e compounds were the most active molecules on Hep3B (IC50 = 5.46 and 12.58 µM, respectively). The 3D results revealed that both 2b and 2e structures confuse the surface of Hep3B cancer cell lines' spheroid formation and force these cells to aggregate into a globular-shaped spheroid. The 2b and 2e showed a comparable interaction pattern to that observed for CA-4 and colchicine within the tubulin-colchicine-binding pocket. The thiophene ring, due to holding a high aromaticity character, participated critically in that observed interaction profile and showed additional advanced interactions over CA-4. The 2b and 2e tubulin complexes showed optimal dynamics trajectories within a time scale of 100 ns at 300 K temperature, which asserts their high stability and compactness. Together, these findings revealed the biomimetic role of 2b and 2e compounds in CA-4 in preventing cancer progression.

Efficient Wide-Bandgap Mixed-Cation and Mixed-Halide Perovskite Solar Cells by Vacuum Deposition.

Vacuum deposition methods are increasingly applied to the preparation of perovskite films and devices, in view of the possibility to prepare multilayer structures at low temperature. Vacuum-deposited, wide-bandgap solar cells based on mixed-cation and mixed-anion perovskites have been scarcely reported, due to the challenges associated with the multiple-source processing of perovskite thin films. In this work, we describe a four-source vacuum deposition process to prepare wide-bandgap perovskites of the type FA1-n Cs n Pb(I1-x Br x )3 with a tunable bandgap and controlled morphology, using FAI, CsI, PbI2, and PbBr2 as the precursors. The simultaneous sublimation of PbI2 and PbBr2 allows the relative Br/Cs content to be decoupled and controlled, resulting in homogeneous perovskite films with a bandgap in the 1.7-1.8 eV range and no detectable halide segregation. Solar cells based on 1.75 eV bandgap perovskites show efficiency up to 16.8% and promising stability, maintaining 90% of the initial efficiency after 2 weeks of operation.

2D materials for conducting holes from grain boundaries in perovskite solar cells.

Grain boundaries in organic-inorganic halide perovskite solar cells (PSCs) have been found to be detrimental to the photovoltaic performance of devices. Here, we develop a unique approach to overcome this problem by modifying the edges of perovskite grain boundaries with flakes of high-mobility two-dimensional (2D) materials via a convenient solution process. A synergistic effect between the 2D flakes and perovskite grain boundaries is observed for the first time, which can significantly enhance the performance of PSCs. We find that the 2D flakes can conduct holes from the grain boundaries to the hole transport layers in PSCs, thereby making hole channels in the grain boundaries of the devices. Hence, 2D flakes with high carrier mobilities and short distances to grain boundaries can induce a more pronounced performance enhancement of the devices. This work presents a cost-effective strategy for improving the performance of PSCs by using high-mobility 2D materials.

Highly Efficient and Stable Perovskite Solar Cells via Modification of Energy Levels at the Perovskite/Carbon Electrode Interface.

Perovskite solar cells (PSCs) have attracted great attention in the past few years due to their rapid increase in efficiency and low-cost fabrication. However, instability against thermal stress and humidity is a big issue hindering their commercialization and practical applications. Here, by combining thermally stable formamidinium-cesium-based perovskite and a moisture-resistant carbon electrode, successful fabrication of stable PSCs is reported, which maintain on average 77% of the initial value after being aged for 192 h under conditions of 85 °C and 85% relative humidity (the "double 85" aging condition) without encapsulation. However, the mismatch of energy levels at the interface between the perovskite and the carbon electrode limits charge collection and leads to poor device performance. To address this issue, a thin-layer of poly(ethylene oxide) (PEO) is introduced to achieve improved interfacial energy level alignment, which is verified by ultraviolet photoemission spectroscopy measurements. Indeed as a result, power conversion efficiency increases from 12.2% to 14.9% after suitable energy level modification by intentionally introducing a thin layer of PEO at the perovskite/carbon interface.

Highly stable and efficient all-inorganic lead-free perovskite solar cells with native-oxide passivation.

There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, all-inorganic cesium tin-germanium triiodide (CsSn0.5Ge0.5I3) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.11%. More importantly, these PSCs show very high stability, with less than 10% decay in efficiency after 500 h of continuous operation in N2 atmosphere under one-sun illumination. The key to this striking performance of these PSCs is the formation of a full-coverage, stable native-oxide layer, which fully encapsulates and passivates the perovskite surfaces. The native-oxide passivation approach reported here represents an alternate avenue for boosting the efficiency and stability of lead-free PSCs.

Gas-solid reaction based over one-micrometer thick stable perovskite films for efficient solar cells and modules.

Besides high efficiency, the stability and reproducibility of perovskite solar cells (PSCs) are also key for their commercialization. Herein, we report a simple perovskite formation method to fabricate perovskite films with thickness over 1 µm in ambient condition on the basis of the fast gas-solid reaction of chlorine-incorporated hydrogen lead triiodide and methylamine gas. The resultant thick and smooth chlorine-incorporated perovskite films exhibit full coverage, improved crystallinity, low surface roughness and low thickness variation. The resultant PSCs achieve an average power conversion efficiency of 19.1 ± 0.4% with good reproducibility. Meanwhile, this method enables an active area efficiency of 15.3% for 5 cm × 5 cm solar modules. The un-encapsulated PSCs exhibit an excellent T80 lifetime exceeding 1600 h under continuous operation conditions in dry nitrogen environment.

Interfacial Modification of Perovskite Solar Cells Using an Ultrathin MAI Layer Leads to Enhanced Energy Level Alignment, Efficiencies, and Reproducibility.

For the first time, we intentionally deposit an ultrathin layer of excess methylammonium iodide (MAI) on top of a methylammonium lead iodide (MAPI) perovskite film. Using photoelectron spectroscopy, we investigate the role of excess MAI at the interface between perovskite and spiro-MeOTAD hole-transport layer in standard structure perovskite solar cells (PSCs). We found that interfacial, favorable, energy-level tuning of the MAPI film can be achieved by controlling the amount of excess MAI on top of the MAPI film. Our XPS results reveal that MAI dissociates at low thicknesses (<16 nm) when deposited on MAPbI3. It is not the MAI layer but the dissociated species that leads to the interfacial energy-level tuning. Optimized interface energetics were verified by solar cell device testing, leading to both an increase of 19% in average steady-state power conversion efficiency (PCE) and significantly improved reproducibility, which is represented by a much lower PCE standard deviation (from 15 ± 2% to 17.2 ± 0.4%).