Solvent-Templated Methylammonium-Based Ruddlesden-Popper Perovskites with Short Interlayer Distances.

Two-dimensional (2D) halide perovskites are exquisite semiconductors with great structural tunability. They can incorporate a rich variety of organic species that not only template their layered structures but also add new functionalities to their optoelectronic characteristics. Here, we present a series of new methylammonium (CH3NH3+ or MA)-based 2D Ruddlesden-Popper perovskites templated by dimethyl carbonate (CH3OCOOCH3 or DMC) solvent molecules. We report the synthesis, detailed structural analysis, and characterization of four new compounds: MA2(DMC)PbI4 (n = 1), MA3(DMC)Pb2I7 (n = 2), MA4(DMC)Pb3I10 (n = 3), and MA3(DMC)Pb2Br7 (n = 2). Notably, these compounds represent unique structures with MA as the sole organic cation both within and between the perovskite sheets, while DMC molecules occupy a tight space between the MA cations in the interlayer. They form hydrogen-bonded [MA···DMC···MA]2+ complexes that act as spacers, preventing the perovskite sheets from condensing into each other. We report one of the shortest interlayer distances (∼5.7-5.9 Å) in solvent-incorporated 2D halide perovskites. Furthermore, the synthesized crystals exhibit similar optical characteristics to other 2D perovskite systems, including narrow photoluminescence (PL) signals. The density functional theory (DFT) calculations confirm their direct-band-gap nature. Meanwhile, the phase stability of these systems was found to correlate with the H-bond distances and their strengths, decreasing in the order MA3(DMC)Pb2I7 > MA4(DMC)Pb3I10 > MA2(DMC)PbI4 ∼ MA3(DMC)Pb2Br7. The relatively loosely bound nature of DMC molecules enables us to design a thermochromic cell that can withstand 25 cycles of switching between two colored states. This work exemplifies the unconventional role of the noncharged solvent molecule in templating the 2D perovskite structure.

Influence of Ionic Additives in the PEDOT:PSS Hole Transport Layers for Efficient Blue Perovskite Light Emitting Diodes.

Ruddlesden-Popper (RP) perovskites have been gaining traction in the development of high-efficiency or blue-emitting perovskite light emitting diodes (PeLEDs) due to the unique energy funneling mechanism, which enhances photoluminescence intensity, and dimensional control, which enables spectral tuning. In a conventional p-i-n device structure, the quality of RP perovskite films, including grain morphology and defects, as well as device performance can be significantly influenced by the underlying hole-transport layer (HTL). Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is commonly used in several PeLEDs as an HTL because of its high electrical conductivity and optical transparency. Nonetheless, the energy level mismatch and exciton quenching caused by PEDOT:PSS often compromises PeLED performance. Herein, we investigate the mitigation of these effects through addition of work-function-tunable PSS Na to the PEDOT:PSS HTL and assess the impact on blue PeLED performance. Surface analysis of the modified PEDOT:PSS HTLs reveals a PSS-rich layer that alleviates exciton quenching at the HTL/perovskite interface. At an optimal concentration of 6% PSS Na addition, an improvement in the external quantum efficiency is observed, with champion blue and sky-blue PeLEDs achieving 4% (480 nm) and 6.36% (496 nm), respectively, while operation stability is prolonged by fourfold.

A facile crush-and-sieve treatment for recycling end-of-life photovoltaics.

The shift towards renewable energy mix has resulted in an exponential growth of the photovoltaic (PV) industry over the past few decades. Parallelly, new recycling technology developments are required to address the incoming volume of waste as they gradually approach their end-of-life (EoL) to realize the concept of a circular economy. Typical recycling processes involve high-temperature burning for separation and release of the PV cells for metal recovery processes. However, this thermal process generates gaseous by-products that cause serious health and environmental issues. Eschewing the need for burning, we demonstrate a simple crush-and-sieve methodology to strategically aids the separation of polymeric and metallic contents. The proposed approach showcased the efficient size-selective separation and generated polymer- and metal-rich fractions. More than 90 % of the total polymer present within the studied wastes was found to be retained in larger sized-particle fractions (F1 and F2). Metal content analysis highlighted the enrichment of highly valuable silver into the smallest sized-particle fraction (F4), accounting up to 70 % and 80 % of total silver present respectively for EVAc and MP. The benefits ripe through this simple crush-and-sieve method offers an attractive pathway for PV recycling process to obtain metal-rich fractions and allow focused recovery of valuable materials through an environmentally friendlier manner.

Upcycling Silicon Photovoltaic Waste into Thermoelectrics.

Two decades after the rapid expansion of photovoltaics, the number of solar panels reaching end-of-life is increasing. While precious metals such as silver and copper are usually recycled, silicon, which makes up the bulk of a solar cells, goes to landfills. This is due to the defect- and impurity-sensitive nature in most silicon-based technologies, rendering it uneconomical to purify waste silicon. Thermoelectrics represents a rare class of material in which defects and impurities can be engineered to enhance the performance. This is because of the majority-carrier nature, making it defect- and impurity-tolerant. Here, the upcycling of silicon from photovoltaic (PV) waste into thermoelectrics is enabled. This is done by doping 1% Ge and 4% P, which results in a figure of merit (zT) of 0.45 at 873 K, the highest among silicon-based thermoelectrics. The work represents an important piece of the puzzle in realizing a circular economy for photovoltaics and electronic waste.

Regulating Vertical Domain Distribution in Ruddlesden-Popper Perovskites for Electroluminescence Devices.

Efficient perovskite light-emitting diodes are designed by employing an ordered vertical domain distribution in quasi-two-dimensional (quasi-2D) perovskites to induce better electron flow to the emitting domains. Dimethyl sulfoxide is added to the precursor solution to tune the crystallization rate and promote the formation of high-m domains near the substrate surface via the one-step deposition method. Optimized deposition conditions yielding a film with favorable energetic landscape for both carrier injection and confinement results in a 4-fold external quantum efficiency (EQE) enhancement with maximum EQE of 5.79%. Better carrier injection is further supported by a turn-on voltage value that is comparable to the band gap of the emitter material (∼2.25 eV).