Controlling conductivity via doping in semiconductor quantum dots is an important part of nanoparticle research. In this report, doping of CdSe quantum dots with indium and tin is explored. High-resolution nanoprobing confirms the presence of indium and tin in the particles and the inclusion of indium into the particles without forming a separate phase. The tin doped CdSe samples show preferential adsorption of tin in quantum dots from the solution during synthesis while incorporation of indium is somewhat statistical. In agreement with the expected n-type behavior, the photoluminescence (PL) of both indium and tin doped samples exhibits a significantly steeper temperature dependence, compared to undoped CdSe quantum dots. Comparison of theory and experimental data suggests that the approximate locations of the dopants levels are at 280 and 100 meV below the conduction band edge of the indium and tin doped quantum dots, respectively. The relative temperature dependent Stokes shifts of the doped samples are larger than those of the undoped sample, suggesting that the electron is backfilling the lowest unoccupied quantum dots levels. The oxidized doped samples exhibit increased polarized band-edge emission. The likely explanation of the polarized emission is that trapping times are fast in the oxidized doped samples compared to the undoped samples.

A new approach is demonstrated to fabricate narrow‐band emission near‐UV microcavity OLEDs (μcOLEDs) with peak emission at ≈385 nm, in near‐perfect alignment with the narrow primary 385 nm absorption band of Pt octaethylporphyrin dye, using 4,4′‐bis(9‐carbazolyl)‐1,1′‐biphenyl (CBP) as the emissive layer. Although OLEDs have been extensively operated at optical wavelengths, only few have achieved near‐UV emission. Yet there is a growing need for portable compact narrow‐band near UV sources for many biomedical and forensic applications. A microcavity effect, due to metallic electrodes enclosing an optical cavity, is employed to achieve the desired narrow peak emission. An Al/Pd bi‐layer anode enables attaining a turn on voltage of 3.8 V and a 4,4′‐cyclohexylidenebis [N,N‐bis (4‐methylphenyl) benzenamine] (TAPC) layer improves electron‐hole recombination in the emissive layer. The fabricated μcOLED is efficiently used as the excitation source in a structurally integrated all‐organic oxygen sensor. Moreover, a CBP‐based combinatorial array of μcOLED pixels is fabricated by varying the thickness of the organic layers to obtain nine sharp, discrete emission peaks from 370 to 430 nm, employed in an all‐organic on‐chip spectrophotometer. The photodetectors are based on P3HT:PCBM (poly(3‐hexylthiophene):[6,6]‐phenyl‐C60‐butyric acid methyl ester) or the more sensitive PTB7:PCBM (PTB7 is polythieno [3,4‐b]‐thiophene‐co‐benzodithiophene). Simulations of the OLEDs' emission are used for analysis of the experimental data, assisting in device fabrication.

conversion efficiency (PCE), [1][2][3][4][5][6][7][8] up to ≈11.5%, was achieved by, e.g., using low bandgap polymers [1][2][3][4][5][6] and developing approaches to control the active layer's morphology utilizing thermal [7] or solvent annealing, [8] mixed solvents, [4] or additives. [1][2][3][4][5][6] Low bandgap polymers improve the PCE by absorbing more sunlight, increasing the short circuit current density J sc (the value without applied bias). A larger open circuit voltage V oc (the forward bias that zeros the current) is achieved by lowering the polymer's highest occupied molecular orbital (HOMO) energy. [1][2][3][4][5] PSC degradation is the main commercialization obstacle. Hence, extensive efforts are directed at understanding degradation [9][10][11][12][13][14][15][16][17] due to, e.g., moisture and oxygen [9][10][11] and light, [11][12][13][14] although the microscopic nature of the generated defects has not been revealed. This paper demonstrates, for the first time, UV/blue photogeneration of metastable carbon dangling bonds (DBs, i.e., threefold coordinated C atoms) akin to the well-known Si DBs that pervade hydrogenated amorphous Si (a-Si:H). [18] The C DBs are revealed via the electron paramagnetic resonance (EPR) of their unpaired spin 1/2 electron after observing the signature EPR of C DBs at g = 2.0029 ± 0.0004 [19][20][21][22][23] in polymer:fullerene films. Importantly, at room temperature the DBs decay slowly in the dark, in sharp contrast to their stability in a-Si:H. [18] However, since the performance of the solar cells does not recover, it is suspected that the C DBs are passivated by, e.g., O-or OH-related groups, rather than the polymer recovering its original configuration.The paper focuses on low-bandgap polymers of alternating benzo[1,2-b:4,5-b′]dithiophene (BDT) and thieno[3,4-b]-thiophene (TT) units (PBDTTTs), [15] which exhibit PCEs up to 10% for inverted cells in polymer:fullerene bulk heterojunction (BHJ) structures. These polymers have high absorption coefficients up to ≈750 nm and high carrier mobilities. [15,16] Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b] thiophene-)-2-carboxylate-2-6-diyl)] (PBDTTT-EFT; Figure 1) has a HOMO level of −5.24 eV and a lowest unoccupied molecular orbital (LUMO) level of −3.66 eV (i.e., bandgap E g = 1.58 eV; Figure 1). [1] BHJ cells of the related PBDTTT-C:PC 70 BM (phenyl-C 70 -butyric-acid-methyl ester) degrade with heat. [17] To improve stability, understanding the defect states' nature and how they act as trapping/recombination centers is important.Intrinsic photodegradation of organic solar cells, theoretically attributed to CH bond rearrangement/breaking, remains a key commercialization barrier. This work presents, via dark electron paramagnetic resonance (EPR), the first experimental evidence for metastable C dangling bonds (DBs) formed by blue/UV irradiation of polymer:fullerene blend films in nitrogen. The DB density increases with irradiation and decreas...

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