Colloidal semiconductor quantum dots (QDs) are attractive materials for realizing highly flexible, solution-processable optical gain media, but they are difficult to use in lasing because of complications associated with extremely short optical-gain lifetimes limited by nonradiative Auger recombination. By combining compositional grading of the QD’s interior for hindering Auger decay with postsynthetic charging for suppressing parasitic ground-state absorption, we can reduce the lasing threshold to values below the single-exciton-per-dot limit. As a favorable departure from traditional multi-exciton–based lasing schemes, our approach should facilitate the development of solution-processable lasing devices and thereby help to extend the reach of lasing technologies into areas not accessible with traditional, epitaxially grown semiconductor materials.

The quest for new materials is one of the main factors propelling recent advances in organic photovoltaics. Star‐shaped small molecules (SSMs) have been proven promising candidates as perspective donor material due to the increase in numbers of excitation pathways caused by the degeneracy of the lowest unoccupied molecular orbital (LUMO) level. In order to unravel the pathways of the initial photon‐to‐charge conversion, the photovoltaic blends based on three different SSMs with a generic structure of N(phenylene‐nthiophene‐dicyanovinyl‐alkyl)3 (n = 1–3), and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) acceptor are investigated by ultrafast photoinduced absorption spectroscopy assisted by density functional theory calculations. It is shown that both electron transfer from SSMs to PC71BM and hole transfer from PC71BM to SSMs are equally significant for generation of long‐lived charges. In contrast, intramolecular (intra‐SSM) charge separation results in geminate recombination and therefore constitutes a loss channel. Overall, up to 60% of long‐lived separated charges are generated at the optimal PC71BM concentrations. The obtained results suggest that further improvement of the SSM‐based solar cells is feasible via optimization of blend morphology and by suppressing the intra‐SSM recombination channel.

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We show that extended TBTBT structure (T = thiophene, B = benzothiadiazole) can be used as an electrondeficient building block for designing conjugated polymers with deeply lying HOMO energy levels and narrow band gaps. The first carbazole−TBTBT copolymer P2 demonstrated power conversion efficiencies exceeding 6% in bulk heterojunction solar cells in combination with advanced operational stability, unlike conventional donor polymers such as PTB7, PBDTTT-CF, etc.