We study the optoelectronic properties of a type-II heterojunction (HJ) comprising a monolayer of the transition metal dichalcogenide (TMDC), WS, and a thin film of the organic semiconductor, 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA). Both theoretical and experimental investigations of the HJ indicate that Frenkel states in the organic layer and two-dimensional Wannier-Mott states in the TMDC dissociate to form hybrid charge transfer excitons at the interface that subsequently dissociate into free charges that are collected at opposing electrodes. A photodiode employing the HJ achieves a peak external quantum efficiency of 1.8 ± 0.2% at a wavelength of 430 ± 10 nm, corresponding to an internal quantum efficiency (IQE) as high as 11 ± 1% in these ultrathin devices. The photoluminescence spectra of PTCDA and PTCDA/WS thin films show that excitons in the WS have a quenching rate that is approximately seven times higher than in PTCDA. This difference leads to strong wavelength dependence in IQE.

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charge collection effi ciency while maintaining a high absorption, the PM-HJ also employs a neat (homogenous) donor and/ or acceptor layer, whose thicknesses are comparable to L D and that clad the mixed region.Unfortunately, such thick and highly absorbing sub-cells typically result in spectral overlaps between elements in the tandem that prevent photons from reaching the back sub-cell, ultimately limiting the total photocurrent. In this work, we overcome this defi ciency by using two relatively thick and strongly absorbing, vacuum-deposited small molecule PM-HJ sub-cells with considerable separation between their absorption maxima, thereby minimizing spectral overlap and maximizing photocurrent. [ 22 ] The front sub-cell adjacent to the transparent anode comprises the primarily orange-to-near infrared (NIR) absorbing donor, 2-((7-(5-(dip-tolylamino)thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)malononitrile (DTDCTB) [23][24][25] blended with C 60 , paired with an ultraviolet-to-yellow absorbing DBP:C 70 back sub-cell. In the front cell, the C 60 intermolecular charge transfer (CT) absorption feature in the green is greatly reduced when diluted in DTDCTB, [ 26 ] thus providing a spectrally complementary system with the back sub-cell. The tandem solar cell broadly covers the solar spectrum from λ = 350 nm to 900 nm, achieving an effi ciency of 10.0 ± 0.2% under 1 sun, AM 1.5G illumination (25 ± 1 °C, 1000 W-m −2 , ASTM G173-03).To further improve the cell performance, a second DBP:C 70 sub-cell is placed immediately adjacent to the transparent anode at the second order optical interference maximum to form a triple-junction OPV. The cell exhibits a power conversion effi ciency of 11.1 ± 0.2%, with V OC of 2.58 ± 0.01 V and the external quantum effi ciency ( EQE ) close to 100% at short wavelengths. Further, this cell employs a thick stack structure that exploits the second order optical interference maximum. Together with a nearly optically lossless BPhen:C 60 electron fi ltering layer connecting the sub-cells, our design approach can lead to achieving even higher effi ciencies in the future.The low band gap DTDCTB absorbs at wavelengths as long as λ = 900 nm. To separate the front (i.e., that nearest the anode) and the back sub-cell (nearest the cathode) absorption spectra, the blue-green absorbing C 60 is used in the front cells as the acceptor, whereas the broadly absorbing C 70 is employed solely in the back sub-cell. The extinction coeffi cients ( k ) of the DTDCTB:C 60 fi lms measured as functions of volume ratio are shown in Figure 1 a. The absorption of a neat C 70 fi lm is also shown for comparison. The DTDCTB exhibits an absorption peak at λ = 700 nm, while C 60 shows two peaks at λ = 360 nm and λ = 450 nm, corresponding to Frenkel-type and intermolecular CT excitations. [ 27 ] The CT feature results from electrons excited from the highest occupied molecular orbital of one molecule to the lowest unoccupied molecular orbital of a nearby C 60 molecule , and hence is sensitive to C 60 concentration...

10×10 photodiode array fabricated on Si and Kapton ® substrateThe 10×10 thin-film In 0.53 Ga 0.47 As p-i-n photodiode arrays are fabricated on both a 500 µm thick semi-insulating Si substrate and a 25 µm thick E-type Kapton ® foil. The fabrication processes of 10×10 arrays are similar to that of the 8×100 photodiode array, although the photodiode dimensions are different. For the 10×10 arrays, the top ring contacts have 20 µm/30 µm inner/outer diameters that define the light detection area. Photodiode mesa diameters are 40 µm, with 100 µm pixel separations. The back side linear contacts are 5 µm wide to connect the photodiode rows, and top linear contact columns are also 5 µm wide. A MgF 2 (81 nm)/TiO 2 (113

Thermophotovoltaic (TPV) systems are a promising technology for distributed conversion of high-temperature heat to electricity. To achieve high conversion efficiency, the transport of sub-bandgap radiation between the thermal emitter and PV cell should be suppressed. This can be achieved by recycling sub-bandgap radiation back to the emitter using a spectrally selective cell. However, conventional TPV cells exhibit limited sub-bandgap reflectance. Here we demonstrate thin-film In0.53Ga0.47As-based structures with high spectral selectivity, including record-high average sub-bandgap reflectance (96%). Selectivity is enabled by short optical paths through a high-quality material fabricated using epitaxial lift-off, high-reflectance back surfaces, and optimized interference. In addition, we use a parallel-plate TPV model to evaluate the impact of specific structural features on performance and to optimize the cell architecture. We show that a dielectric spacer between InGaAs and the Au back surface is an important feature that enables a predicted TPV efficiency above 50% (with a power output of 2.1 W/cm2), significantly higher than current TPV devices. This work provides guidelines for the design of high-efficiency, low-cost TPV generators.