Two-dimensional BiTeI as a novel perovskite additive for printable perovskite solar cells

Dopant-Free Spiro-OMe2 Imidazole-Based Hole-Transporting Material for Stable and Low-Cost Organic-Inorganic Perovskite Solar Cell

The engineering of charge transport materials, with electronic characteristics that result in effective charge extraction and transport dynamics, is pivotal for the realization of efficient perovskite solar cells (PSCs). Herein, we elucidate the critical role of terminal substituent methoxy groups (-OCH3) on the bandgap tuning of the spiro-like hole transport materials (HTMs) to realize performant and cost-effective PSCs. By considering spiro-OMeTAD as the benchmark HTM, we kept the backbone of spiro while replacing diphenylamine with phenanthrenimidazole. This approach significantly decreases the cost of spiro-OMeTAD by reducing the cost of the ancillary group from 0.051 to 0.012 $/g. By increasing the number of methoxy groups on the ancillary ligand from four to eight, the power conversion efficiency (PCE) of the corresponding PSCs containing dopants passed from 17.10% to 18.70%, approaching the value achieved using spiro-OMeTAD containing dopants (PCE = 19.26%). Remarkably, the devices based on dopant-free spiro-OMeTAD have shown a significant loss of PCE, which decreased from 12.9% to 10.1% after 300 h (to 8.2% after 600 h) of light soaking at an open circuit voltage. On the contrary, the cells based on the designed dopant-free HTM demonstrated optimal PCE retention, experiencing a minor drop from 14.4% to 14.1% and 13.2% after 300 and 600 h, respectively, of light soaking at open-circuit voltage.

Ferrovalley and Quantum Anomalous Hall Effect in Janus TiTeCl Monolayer

Ferrovalley materials are garnering significant interest for their potential roles in advancing information processing and enhancing data storage capabilities. This study utilizes first-principles calculations to determine that the Janus monolayer TiTeCl exhibits the properties of a ferrovalley semiconductor. This material demonstrates valley polarization with a notable valley splitting of 80 meV. Additionally, the Berry curvature has been computed across the first Brillouin zone of the monolayer TiTeCl. The research also highlights that topological phase transitions ranging from ferrovalley and half-valley metals to quantum anomalous Hall effect states can occur in monolayer TiTeCl under compressive strains ranging from -1% to 0%. Throughout these strain changes, monolayer TiTeCl maintains its ferromagnetic coupling. These characteristics make monolayer TiTeCl a promising candidate for the development of new valleytronic and topological devices.

A Low-Cost and Lithium-Free Hole Transport Layer for Efficient and Stable Normal Perovskite Solar Cells

The most widely used material as a hole-transport layer (HTL) for effective normal perovskite solar cells (PSCs) is still 2,2',7,7'-Tetrakis[N, N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), which requires heavy doping with the hydroscopic Lithium bis(trifluoromethanesulfonyl)imide (Li-ΤFSI). However, the long-term stability and performance of PCSs are frequently hampered by the residual insoluble dopants in the HTL, Li⁺ diffusion throughout the device, dopant by-products, and the hygroscopic nature of Li-TFSI. Due to the high cost of Spiro-OMeTAD, alternative efficient low-cost HTLs, such as octakis(4-methoxyphenyl)spiro[fluorene-9,9'-xanthene]-2,2',7,7'-tetraamine) (X60), have attracted attention. However, they require doping with Li-TFSI, and the devices develop the same Li-TFSI-derived problems. Here, we propose Li-free 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI) as an efficient p-type dopant of X60, resulting in a high-quality HTL with enhanced conductivity and deeper energy levels The optimized X60:EMIM-TFSI-enabled devices exhibit a higher efficiency of 21.85% and improved stability, compared to the Li-TFSI-doped X60 devices. The stability of the optimized EMIM-TFSI-doped PSCs is greatly improved, and after 1200 hr of storage under ambient conditions, the resulting PSCs maintain 85% of the initial PCE. These findings offer a fresh method for doping the cost effective X60 as the HTL with a Li-free alternative dopant for efficient, cheaper, and reliable planar PSCs.