considered as one of the most promising green-energy technologies. [1][2][3][4] From the past several years, with the advents of start-of-the-art Y-series non-fullerene acceptors (NFAs) (Y6, Y6-BO, BTIC-2Cl-γCF 3 , BTP-eC9, L8-BO, and so on) in terms of novel electron-deficient core, dithienothiophen[3.2-b]pyrrolobenzothiadiazole, BTP, [5][6][7][8][9][10] the recording power conversion efficiencies (PCEs) have exceeded 19% in single-junction configuration and over 20% certified PCE based on tandem solar cells has been reported recently. [11,12] As the exciton splitting, charge generation, transport, and extraction are highly dependent on the microstructure morphology and mesoscopic aggregation state in bulk heterojunction (BHJ) photoactive layer. [13] Correspondingly, considerable morphology control strategies have been proposed to enhance crystallinity and manipulate phase separation behaviors for the promotion of photovoltaic characteristics. For example, solvent additive engineering is a promising approach to fine-tune nanomorphology. Despite the increment of performance, such a strategy worsen the device reproducibility and long-term operational stability due to the low volatilization property. [14][15][16][17] Besides, the ternary blend (introducing a third Volatile solids with symmetric π-backbone are intensively implemented on manipulating the nanomorphology for improving the operability and stability of organic solar cells. However, due to the isotropic stacking, the announced solids with symmetric geometry cannot modify the microscopic phase separation and component distribution collaboratively, which will constrain the promotion of exciton splitting and charge collection efficiency. Inspired by the superiorities of asymmetric configuration, a novel process-aid solid (PAS) engineering is proposed. By coupling with BTP core unit in Y-series molecule, an asymmetric, volatile 1,3-dibromo-5-chlorobenzene solid can induce the anisotropic dipole direction, elevated dipole moment, and interlaminar interaction spontaneously. Due to the synergetic effects on the favorable phase separation and desired component distribution, the PAS-treated devices feature the evident improvement of exciton splitting, charge transport, and collection, accompanied by the suppressed trap-assisted recombination. Consequently, an impressive fill factor of 80.2% with maximum power conversion efficiency (PCE) of 18.5% in the PAS-treated device is achieved. More strikingly, the PAStreated devices demonstrate a promising thickness-tolerance character, where a record PCE of 17.0% is yielded in PAS devices with a 300 nm thickness photoactive layer, which represents the highest PCE for thick-film organic solar cells.

Lead halide perovskite nanocrystals (LHP NCs) have emerged as next-generation semiconductor materials with outstanding optical and optoelectronic properties. Because of the high surface-to-volume ratio, the optical and optoelectronic performance and the colloidal stability of LHP NCs largely depend on their surface chemistry, especially the ligands and surface termination. On one hand, the capping ligands improve the colloidal stability and luminescence; on the other hand the highly dynamic binding nature of ligands is detrimental to the colloidal stability and photoluminescence of LHP NCs. In addition, the surface functionalization with desired molecules induces new functionalities such as chirality, light harvesting, and triplet sensitization through energy/electron transfer or use as X-ray detectors. In this review, we present the current understanding of an atomic view of the surface chemistry of colloidal LHP NCs, including crystal termination, vacancies, and different types of capping ligands. Furthermore, we discuss the ligand-induced functionalities, including photocatalysis and chirality.

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