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Abstract The interface between the hole transport layer (HTL) and perovskite in p‐i‐n perovskite solar cells (PSCs) plays a vital role in the device performance and stability. However, the impact of this interface on the vertical phase segregation of mixed halide perovskite remains insufficiently understood. This work systematically investigates the impact of chemical and electronic properties of HTL on vertical halide segregation of mixed‐halide perovskites. This work shows that incorporating a poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA)/CuI_xBr_1‐xbilayer as the HTL significantly suppresses light‐induced vertical phase segregation in MAPb(I_0.7Br_0.3)₃. This work uses grazing‐incidence X‐ray diffraction (GIXRD) to capture the depth‐resolved composition change of MAPb(I_0.7Br_0.3)₃at the interface and within the bulk under illumination. By changing the illumination direction and the electronic properties of HTL, this work elucidates the roles of charge carrier extraction and interfacial defects on vertical phase segregation. The PTAA/CuI_xBr_1‐xbilayer, with its synergistic passivation and efficient hole extraction ability, stabilizes the interface and bulk of the mixed halide perovskite layer and prevents phase segregation. This work underscores that synergetic passivation and efficient hole extraction pack a more powerful punch for arresting the vertical phase segregation in mixed‐halide perovskite. 

Spin chemistry of photogenerated spin-correlated radical pairs (SCRPs) offers a practical approach to control chemical reactions and molecular emissions using weak magnetic fields. This capability to harness magnetic field effects (MFEs) paves the way for developing SCRPs-based molecular qubits. Here, we introduce a new series of donor-chiral bridge-acceptor (D-χ-A) molecules that demonstrate significant MFEs on fluorescence intensity and lifetime in solution at room temperature – critical for quantum sensing. By precisely tuning the donor site through torsional locking, distance extension, and planarization, we achieved remarkable control over key quantum properties, including field-response range and linewidth. In the most responsive systems, emission lifetimes increased by over 200%, and total emission intensity was modulated by up to 30%. This level of tunability, and rational design principle of optically addressable molecular qubits, represents a major leap toward functional synthetic molecular qubits, advancing the field of molecular quantum technologies. 

The degree of torsional hindrance can significantly contribute to anti-Arrhenius behavior of charge recombination, wherein recombination rates decrease as temperature increases. 

Photogenerated spin-correlated radical pairs (SCRPs) in electron donor–bridge–acceptor (D–B–A) molecules can act as molecular qubits and inherently spin qubit pairs. SCRPs can take singlet and triplet spin states, comprising the quantum superposition state. Their synthetic accessibility and well-defined structures, together with their ability to be prepared in an initially pure, entangled spin state and optical addressability, make them one of the promising avenues for advancing quantum information science. Coherence between two spin states and spin selective electron transfer reactions form the foundation of using SCRPs as qubits for sensing. We can exploit the unique sensitivity of the spin dynamics of SCRPs to external magnetic fields for sensing applications including resolution-enhanced imaging, magnetometers, and magnetic switch. Molecular quantum sensors, if realized, can provide new technological developments beyond what is possible with classical counterparts. While the community of spin chemistry has actively investigated magnetic field effects on chemical reactions via SCRPs for several decades, we have not yet fully exploited the synthetic tunability of molecular systems to our advantage. This review offers an introduction to the photogenerated SCRPs-based molecular qubits for quantum sensing, aiming to lay the foundation for researchers new to the field and provide a basic reference for researchers active in the field. We focus on the basic principles necessary to construct molecular qubits based on SCRPs and the examples in quantum sensing explored to date from the perspective of the experimentalist.