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Compared to the most-studied non-fullerene acceptors (NFAs) with linear skeletons, multi-dimensional NFAs with largely conjugated extension in multiple directions may contribute to more efficient organic solar cells (OSCs) due to...

It has been proposed that isotope effects could effectively downshift intramolecular vibrational frequencies of lightharvesting materials, thereby reducing the non-radiative recombination from the charge-transfer (CT) state to the ground state (GS) and achieving a smaller non-radiative energy loss (ΔE loss non-rad ) theoretically in organic solar cells (OSCs). However, there are no systematic experimental studies to address such a crucial issue: can isotope effects enable OSCs to achieve a smaller ΔE loss non-rad and why? Herein, we constructed 29 non-fullerene acceptors (NFAs) by isotope substitution on different functional groups based on four high-performance NFA systems and further investigated their photovoltaic performance systematically. Large-scale statistical experimental and theoretical analyses indicate no significant difference of PCE and ΔE loss non-rad due to the intrinsically very weak electron-vibration coupling between the CT state and GS (EVC CT-GS ) and largely unimpacted coupling strength (t CT-LE ) between the CT and local exciton states. Also based on theoretical results from the Huang−Rhys factor, although different vibration modes could have different influences on the strength of EVC CT-GS , all are quite small. Both experimental and theoretical results suggest that an isotope strategy may not be a feasible way to significantly improve PCEs of high-performance OSCs by reducing ΔE loss non-rad at the current stage. Article pubs.acs.org/cm

2D Ruddlesden–Popper (2D RP) perovskite, with attractive environmental and structural stability, has shown great application in perovskite solar cells (PSCs). However, the relatively inferior photovoltaic efficiencies of 2D PSCs limit their further application. To address this issue, β‐​fluorophenylethanamine (β‐​FPEA) as a novel spacer cation is designed and employed to develop stable and efficient quasi‐2D RP PSCs. The strong dipole moment of the β‐​FPEA enhances the interactions between the cations and [PbI6]4− octahedra, thus improving the charge dissociation of quasi‐2D RP perovskite. Additionally, the introduction of the β‐​FPEA cation optimizes the energy level alignment, improves the crystallinity, stabilizes both the mixed phase and a‐FAPbI3 phase of the quasi‐2D RP perovskite film, prolongs the carrier diffusion length, increases the carrier lifetime and decreases the trap density. By incorporating the β‐​FPEA, the quasi‐2D RP PSCs exhibit a power conversion efficiency (PCE) of 16.77% (vs phenylethylammonium (PEA)‐based quasi‐2D RP PSCs of 12.81%) on PEDOT:PSS substrate and achieve a champion PCE of 19.11% on the PTAA substrate. It is worth noting that the unencapsulated β‐​FPEA‐based quasi‐2D RP PSCs exhibit considerably improved thermal and moisture stability. These findings provide an effective strategy for developing novel spacer cations for high‐performance 2D RP PSCs.

In this paper, we conducted DFT and TDDFT calculations on three double heteroleptic Cu(i) complexes to understand how different substituents on N^N ligands influence the phosphorescence quantum yield (PLQY). Both radiative and nonradiative decay processes were thoroughly investigated. Factors that determine the rate of radiative process (kr) were considered, including the lowest triplet excited state E(T1), the transition dipole moment MSm,j of the Sm → S0 transition, the spin-coupled matrix element SOC, and the singlet-triplet splitting energies ΔE(Sm-T1). The results indicate that E(T1), MSm,j and SOC increase and ΔE(Sm-T1) decreases upon introducing -Ph and -CH2- groups on the N^N ligands. The net results lead to a gradual increase of kr in the three Cu(i) complexes, from 1 (0.48 × 104 s-1) to 2 (0.64 × 104 s-1) and then to 3 (1.61 × 104 s-1). The rate of nonradiative decay process (knr) was computed by a convolution method. We explored how knr is determined by SOC between T1 and S0 states (T1|SOC|S02), effective energy gap ΔE' and the Huang-Rhys factor (S). We found that T1|SOC|S02 and ΔE' contribute significantly to knr, but S does not determine the order of knr. knr gradually decreases from complex 1 (2.51 × 106 s-1) to 2 (0.32 × 106 s-1) and then to 3 (0.14 × 106 s-1) after introducing -Ph and -CH2- groups on the N^N ligands. The computed PLQYs for the three complexes are 1: 0.0019, 2: 0.0198, and 3: 0.1011. These are quantitatively consistent with the experimental observation (1: 0.0028, 2: 0.0061, and 3: 0.1000).