n the current intermedíate band solar cells made with InAs quantum dots (QDs) in GaAs, the ransitions by absorption of photons between the intermedíate band and the conduction band for llumination normal to the cell surface is very weak or, more often, undetectable. We model the QD as a jarallelepiped potential well and calcúlate the envelope function of the electrón wavefunctions. By jbtaining the dipolar matrix elements we find that, with the present shapes, this absorption is ,'orbidden or very weak. Deeper QDs with smaller base dimensions should be made to permit this

A colloidal deposition technique is presented to construct long-range ordered hybrid arrays of self-assembled quantum dots and metal nanoparticles. Quantum dots are promising for novel opto-electronic devices but, in most cases, their optical transitions of interest lack sufficient light absorption to provide a significant impact in their implementation. A potential solution is to couple the dots with localized plasmons in metal nanoparticles. The extreme confinement of light in the near-field produced by the nanoparticles can potentially boost the absorption in the quantum dots by up to two orders of magnitude.In this work, light extinction measurements are employed to probe the plasmon resonance of spherical gold nanoparticles in lead sulfide colloidal quantum dots and amorphous silicon thin-films. Mie theory computations are used to analyze the experimental results and determine the absorption enhancement that can be generated by the highly intense near-field produced in the vicinity of the gold nanoparticles at their surface plasmon resonance.The results presented here are of interest for the development of plasmon-enhanced colloidal nanostructured photovoltaic materials, such as colloidal quantum dot intermediate-band solar cells.

The three-terminal heterojunction bipolar transistor solar cell (HBTSC) concept enables the realization of a monolithic double-junction device with individual current extraction. We present an HBTSC realized by a heterojunction of GaInP and GaAs. The one-sun open-circuit voltage (VOC ) of the top and bottom junctions are 1.33 V and 0.99 V, respectively, while fill factors (FF) are above 80%. At one-sun illumination, reducing one junction's bias from VOC to maximum power point degrades the performance of the other junction only slightly (< 0.5% efficiency loss). These results demonstrate the potential of the HBTSC concept to produce high-efficiency independently connected double-junction solar cells.

Independent current extraction in multi-junction solar cells has gained attention in recent years because it can deliver higher annual energy yield and can work for more semiconductor material combinations than the more established series-connected multi-junction technology. The heterojunction bipolar transistor solar cell concept (HBTSC) was recently proposed as a simple, compact and cost-effective multi-terminal device structure that allows independent current extraction. It consists of only three main layers: emitter, base and collector. In this work we use a drift-diffusion model to analyze important aspects in the design of an HBTSC structure based on typical III-V semiconductor materials. We find that carrier injection from the emitter into the collector (transistor effect) degrades the opencircuit voltage of the top sub-cell, but this risk can be eliminated by optimizing the base design. We find requirements for the base layer which are, in principle, achievable in the context of current III-V semiconductor technology.Index Terms -Drift-diffusion model, heterojunction bipolar transistor solar cell, multi-junction solar cell, novel photovoltaic concept.

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