Efficiency enhancement calculations of state-of-the-art solar cells by luminescent layers with spectral shifting, quantum cutting, and quantum tripling function

Solar cells of which the efficiency is not limited by the Shockley-Queisser limit can be obtained by integrating a luminescent spectral conversion layer into the cell structure. We have calculated the maximum efficiency of state-of-the-art c-Si, pc-Si, a-Si, CdTe, GaAs, CIS, CIGS, CGS, GaSb, and Ge solar cells with and without an integrated...

Current-induced nanogap formation and graphitization in boron-doped diamond films

A high-current annealing technique is used to fabricate nanogaps and hybrid diamond/graphite structures in boron-doped nanocrystalline diamond films. Nanometer-sized gaps down to ?1?nm are produced using a feedback-controlled current annealing procedure. The nanogaps are characterized using scanning electron microscopy and electronic transport...

Increased carrier generation rate in Si nanocrystals in SiO2 investigated by induced absorption

We report on investigations of optical generation of carriers in Si nanocrystals embedded in SiO2 matrix by time-resolved induced absorption technique. Results obtained for excitation below and above twice the bandgap energy h??<?2Eg and h??>?2Eg show very similar decay characteristics (within ?resolution ? 100 fs). When intensity of the signal...

Hydrogenated amorphous silicon deposited under accurately controlled ion bombardment using pulse-shaped substrate biasing

We have applied pulse-shaped biasing to the expanding thermal plasma deposition of hydrogenated amorphous silicon at substrate temperatures ? 200?°C and growth rates around 1 nm/s. Substrate voltage measurements and measurements with a retarding field energy analyzer demonstrate the achieved control over the ion energy distribution for...

Generation and transport of photoexcited electrons in single-crystal diamond

We report time-dependent photocurrent and transport measurements of sub-bandgap photoexcited carriers in nitrogen-rich (type Ib), single-crystal diamond. Transient carrier dynamics are characteristic of trapping conduction with long charge storage lifetimes of ? 3?hours. By measuring the photoexcited Hall effect, we confirm that the charge...

Electronic coupling of colloidal CdSe nanocrystals monitored by thin-film positron-electron momentum density methods

The effect of temperature controlled annealing on the confined valence electron states in CdSe nanocrystal arrays, deposited as thin films, was studied using two-dimensional angular correlation of annihilation radiation. A reduction in the intensity by ?35% was observed in a feature of the positron annihilation spectrum upon removal of the...

Determination of the mobility gap of intrinsic ?c-Si:H in p-i-n solar cells

Microcrystalline silicon (?c-Si:H) is a promising material for application in multijunction thin-film solar cells. A detailed analysis of the optoelectronic properties is impeded by its complex microstructural properties. In this work we will focus on determining the mobility gap of ?c-Si:H material. Commonly a value of 1.1?eV is found, similar...

Evidence of noncascade intracenter electron relaxation in shallow donor centers in silicon

Noncascade relaxation of photoexcited electrons on ionized donor centers has been observed in silicon doped by arsenic (Si:As) at low temperatures. Emission spectra of the Si:As terahertz intracenter laser give evidence of specific channels for the electron relaxation through low-lying donor states. The dominating relaxation channels strongly...

Structural modulation and electronic structural features in the charge ordered state of La0.5Sr1.5MnO4

Formation and stability of rocksalt ZnO nanocrystals in MgO

Coimplantation of Zn and O ions into a single crystalline MgO and subsequent thermal annealing were applied in the synthesis of ZnO nanocrystals. Electron microscopy showed that rocksalt instead of wurtzite ZnO stabilizes for relatively large nanocrystals up to ~15?nm, resulting from its small lattice mismatch with MgO of ~1.7%. The vacancies...

Crystal structure and band gap determination of HfO2 thin films

Valence electron energy loss spectroscopy (VEELS) and high resolution transmission electron microscopy (HRTEM) are performed on three different HfO2 thin films grown on Si (001) by chemical vapor deposition (CVD) or atomic layer deposition (ALD). For each sample the band gap (Eg) is determined by low-loss EELS analysis. The Eg values are then...

Charge deep-level transient spectroscopy study of high-energy-electron-beam-irradiated hydrogenated amorphous silicon

We present a study of changes in the defect density of states in hydrogenated amorphous silicon (a-Si:H) due to high-energy electron irradiation using charged deep-level transient spectroscopy. It was found that defect states near the conduction band were removed, while in other band gap regions the defect-state density increased. A similar...

Temperature dependent spectroscopic studies of the electron delocalization dynamics of excited Ce ions in the wide band gap insulator, Lu2SiO5

Electron delocalization processes of optically excited states of Ce3+ impurities in Lu2SiO5 were investigated by means of a temperature and spectrally resolved photoconductivity study. By monitoring separately the strength of the photocurrent resulting from excitation into each of the Ce3+?5d absorption bands, over a broad temperature region,...

Polymeric amorphous carbon as p-type window within amorphous silicon solar cells

Amorphous carbon (a-C) has been shown to be intrinsically p-type, and polymeric a-C (PAC) possesses a wide Tauc band gap of 2.6 eV. We have replaced the p-type amorphous silicon carbide layer of a standard amorphous silicon solar cell with an intrinsic ultrathin layer of PAC. The thickness of the p layer had to be reduced from 9 to 2.5 nm in...