Modeling Multiple Quantum Well and Superlattice Solar Cells

The inability of a single-gap solar cell to absorb energies less than the band-gap energy is one of the intrinsic loss mechanisms which limit the conversion efficiency in photovoltaic devices. New approaches to “ultra-high” efficiency solar cells include devices such as multiple quantum wells (QW) and superlattices (SL) systems in the intrinsic region of a p-i-n cell of wider band-gap energy (barrier or host) semiconductor. These configurations are intended to extend the absorption band beyond the single gap host cell semiconductor. A theoretical model has been developed to study the performance of the strain-balanced GaAsP/InGaAs/GaAs MQWSC, and GaAs/GaInNAs MQWSC or SLSC. Our results show that conversion efficiencies can be reached which have never been obtained before for a single-junction solar cell.

Influence of Ring Oxidation-Induced Stack Faults on Efficiency in Silicon Solar Cells

We observe a strong correlation between the ring oxidation-induced stack faults （OISF） formed in the course of phosphor diffusion and the efficiency of Czochralski-grown silicon solar cells. The main reason for ring-OISF formation and growth in substrate is the silicon oxidation and phosphorus diffusion process induced silicon selfinterstitial point defect during POCI3 diffusion. The decreasing of minority carrier diffusion length in crystal silicon solar cell induced by ring-OISF defects is identified to be one of the major causes of efficiency loss.

Excellent Passivation of p-Type Si Surface by Sol-Gel Al2O3 Films

Al2O3 films with a thickness of about lOOnm synthesized by spin coating and thermally treated are applied for field-induced surface passivation of p-type crystalline silicon. The level of surface passivation is determined by techniques based on photoconductance. An effective surface recombination velocity below lOOcm/s is obtained on 10Ωcm p-type c-Si wafers （Cz Si）. A high density of negative fixed charges in the order of 10^12 cm^-2 is detected in the Al2O3 films and its impact on the level of surface passivation is demonstrated experimentally. Furthermore, a comparison between the surface passivation achieved for thermal SiO2 and plasma enhanced chemical vapor deposition SiNx ：H films on the same c-Si is presented. The high negative fixed charge density explains the excellent passivation of p-type c-S/by Al2O3.

Influence of annealing temperature on passivation performance of thermal atomic layer deposition Al_2O_3 films

Chemical and field-effect passivation of atomic layer deposition （ALD） Al2O3 films are investigated, mainly by corona charging measurement. The interface structure and material properties are characterized by transmission electron microscopy （TEM） and X-ray photoelectron spectroscopy （XPS）, respectively. Passivation performance is improved remarkably by annealing at temperatures of 450 ℃ and 500 ℃, while the improvement is quite weak at 600 ℃, which can be attributed to the poor quality of chemical passivation. An increase of fixed negative charge density in the films during annealing can be explained by the Al2O3/Si interface structural change. The Al–OH groups play an important role in chemical passivation, and the Al–OH concentration in an as-deposited film subsequently determines the passivation quality of that film when it is annealed, to a certain degree.

Elaboration of ZnO nanowires by solution based method,characterization and solar cell applications

ZnO nanowires（NWs）layers have been synthesized using a two-step chemical solution method on ITO glass substrates coated with ZnO seeds at different immersing times.The structures,morphology and optical properties of the synthesized ZnO NWs have been investigated.The prepared ZnO NWs have an obvious polycrystalline hexangular wurtzite structure and are preferentially oriented along the c-axis（002）.FESEM micrographs showed that the prepared ZnO NWs are close to being vertically grown and more densely at higher immersing times.Poly[2-methoxy-5（2-′-ethyl-hexyloxy）-1,4-phenylenevinylene],MEH-PPV,was used as an active layer to prepare three samples of MEH-PPV/ZnO solar cell based on ZnO NWs that were prepared at different immersing times.A maximum power conversion efficiency of 0.812%was achieved for MEH-PPV/ZnO solar cell prepared at a higher immersing time.The improved efficiency may be attributed to the enhancement of both open-circuit voltage and fill factor.