Toward Improving Triplet Energy Transfer from Tetracene to Silicon Using a Covalently Bound Tetracene Seed Layer.

Silicon solar cells are operating close to the theoretical maximum efficiency limit. To increase their efficiency beyond this limit, it is necessary to decrease energy losses occurring for high-energy photons. A sensitizing layer of singlet-fission material can in principle double the current generated by high-energy photons, and significantly reduce energy losses from high-energy photons within the solar cell. Here, we construct a model of such a solar cell, using Si(111) surfaces and tetracene. To increase the energy transfer between the two layers, a series of tetracene derivatives was synthesized, and the molecules were covalently attached onto the silicon surface as a seed layer. Using X-ray diffraction, a shift in crystal structure and ordering of the tetracene close to the seed layer can be observed. Unfortunately, the effect on the energy transfer was limited, showing a need for further investigations into the effect of the seed layer.

Sulfur-Phenolate Exchange as a Mild, Fast, and High-Yielding Method toward the Synthesis of Sulfonamides.

Sulfonamides have many important biological applications, yet their synthesis often involves long reaction times under dry and non-ambient conditions. Here we report the synthesis of a large range of sulfonamides at room temperature using 4-nitrophenyl benzylsulfonate as a starting material. Sulfonamides were prepared from a wide range of aliphatic, linear, and cyclic amines, anilines, and N-methylanilines. The yields and reaction times observed here were comparable to or better than those reported previously, establishing sulfur-phenolate exchange as a viable alternative.

Sulfur-Phenolate Exchange As a Fluorine-Free Approach to S(VI) Exchange Chemistry on Sulfonyl Moieties.

SuFEx chemistry has recently evolved as next-generation click chemistry. However, in most SuFEx syntheses, additional reagents/catalysts and carefully controlled conditions are still needed. Here, we aim to further generalize S(VI) exchange chemistry, using 4-nitrophenyl phenylmethanesulfonate as example, in which the nitrophenolate group is exchanged for a wide range of (substituted) phenols and alkyl alcohols. Quantitative yields were reached within 10 min under ambient conditions and required only filtering through silica as workup.

Change in Tetracene Polymorphism Facilitates Triplet Transfer in Singlet Fission-Sensitized Silicon Solar Cells.

Singlet fission in tetracene generates two triplet excitons per absorbed photon. If these triplet excitons can be effectively transferred into silicon (Si), then additional photocurrent can be generated from photons above the bandgap of Si. This could alleviate the thermalization loss and increase the efficiency of conventional Si solar cells. Here, we show that a change in the polymorphism of tetracene deposited on Si due to air exposure facilitates triplet transfer from tetracene into Si. Magnetic field-dependent photocurrent measurements confirm that triplet excitons contribute to the photocurrent. The decay of tetracene delayed photoluminescence was used to determine a transfer efficiency of ∼36% into Si. Our study suggests that control over the morphology of tetracene during the deposition will be of great importance to boost the triplet transfer yield further.

Fast room-temperature functionalization of silicon nanoparticles using alkyl silanols.

Silicon nanoparticles (Si NPs) are a good alternative to conventional heavy metal-containing quantum dots in many applications, due to their low toxicity, low cost, and the high natural abundance of the starting material. Recently, much synthetic progress has been made, and crystalline Si NPs can now be prepared in a matter of hours. However, the passivation of these particles is still a time-consuming and difficult process, usually requiring high temperatures and/or harsh reaction conditions. In this paper, we report an easy method for the room-temperature functionalization of hydrogen-terminated Si NPs. Using silanol compounds, a range of functionalized Si NPs could be produced in only 1 h reaction time at room temperature. The coated NPs were fully characterized to determine the efficiency of binding and the effects of coating on the optical properties of the NPs. It was found that Si NPs were effectively functionalized, and that coated NPs could be extracted from the reaction mixture in a straightforward manner. The silanol coating increases the quantum yield of fluorescence, decreases the spectral width and causes a small (∼50 nm) blue-shift in both the excitation and emission spectra of the Si NPs, compared to unfunctionalized particles.