A simple optical model is presented to describe the influence of a planar luminescent down-shifting layer (LDSL) on the external quantum efficiencies of photovoltaic solar cells. By employing various visible light-emitting LDSLs based on CdTe quantum dots or CdSe/CdS core–shell quantum dots and tetrapods, we show enhancement in the quantum efficiencies of thin-film CdTe/CdS solar cells predominantly in the ultraviolet regime, the extent of which depends on the photoluminescence quantum yield (PLQY) of the quantum dots. Similarly, a broad enhancement in the quantum efficiencies of crystalline Si solar cells, from ultraviolet to visible regime, can be expected for an infrared emitting LDSL based on PbS quantum dots. A PLQY of 80% or higher is generally required to achieve a maximum possible short-circuit current increase of 16 and 50% for the CdTe/CdS and crystalline Si solar cells, respectively. As also demonstrated in this work, the model can be conveniently extended to incorporate LDSLs based on organic dyes or upconverting materials.

A Pt(II) alkynyl terpyridine complex containing a carbazole moiety, [Pt((t)Bu(3)tpy)(C≡C-C(6)H(4)-4-carbazole-9)](+) ((t)Bu(3)tpy = 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine) 1, has been synthesized and characterized. The photophysical behavior has been studied, and the molecular structure has been determined by X-ray crystallography. The complex was found to exhibit intense electrogenerated chemiluminescence (ECL) using peroxydisulfate (S(2)O(8)(2-)) as coreactant in acetonitrile/water (1-25%, v/v) mixture at both glassy carbon and gold electrodes, representing the first ECL example of the Pt(II) alkynyl family. The ECL was produced at potential corresponding to the first reduction wave (-0.90 V vs SCE), significantly shifted by ∼0.65 V toward more positive potential compared with that of [Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine). The ECL spectrum was found to be identical to the photoluminescence spectrum recorded in the same medium, indicating the formation of the same excited state of dπ(Pt) → π*((t)Bu(3)tpy) (3)MLCT mixed with π(C≡CR) → π*((t)Bu(3)tpy) (3)LLCT in both cases. The ECL mechanism was proposed involving the formation of the strongly oxidizing intermediate, SO(4)(•-), mainly generated during the catalytic reduction of S(2)O(8)(2-) by the electrogenerated 1(-). Chemiluminescence of 1/S(2)O(8)(2-) based on reduction with Al metal is also described.

A series of platinum(II) alkynyl-based sensitizers has been synthesized and found to show light-to-electricity conversion properties. These dyes were developed as sensitizers for the application in nanocrystalline TiO(2) dye-sensitized solar cells (DSSCs). Their photophysical and electrochemical properties were studied. The excited-state property was probed using nanosecond transient absorption spectroscopy, which showed the formation of a charge-separated state that arises from the intramolecular photoinduced charge transfer from the platinum(II) alkynylbithienylbenzothiadiazole moiety (donor) to the polypyridyl ligand (acceptor). A lifetime of 3.4 μs was observed for the charge-separated state. A dye-sensitized solar cell based on one of the complexes showed a short-circuit photocurrent of 7.12 mA cm(-2), an open circuit voltage of 780 mV, and a fill factor of 0.65, thus giving an overall power conversion efficiency of 3.6%.