Geometrical optimization and electrical performance comparison of thin-film tandem structures based on pm-Si:H and µc-Si:H using computer simulation

International audienceThis article investigates the optimal efficiency of a photovoltaic system based on a silicon thin film tandem cell using polymorphous and microcrystalline silicon for the top and bottom elementary cells, respectively. Two ways of connecting the cells are studied and compared: (1) a classical structure in which the two cells are electrically and optically coupled; and (2) a new structure for which the "current-matching" constraint is released by the electrical decoupling of the two cells. For that purpose, we used a computer simulation to perform geometrical optimization of the studied structures as well as their electrical performance evaluation. The simulation results show that the second structure is more interesting in terms of efficiency

Characterization of silicon heterojunctions for solar cells

Conductive-probe atomic force microscopy (CP-AFM) measurements reveal the existence of a conductive channel at the interface between p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) as well as at the interface between n-type a-Si:H and p-type c-Si. This is in good agreement with planar conductance measurements that show a large interface conductance. It is demonstrated that these features are related to the existence of a strong inversion layer of holes at the c-Si surface of (p) a-Si:H/(n) c-Si structures, and to a strong inversion layer of electrons at the c-Si surface of (n) a-Si:H/(p) c-Si heterojunctions. These are intimately related to the band offsets, which allows us to determine these parameters with good precision

Conductive-probe atomic force microscopy characterization of silicon nanowire

The electrical conduction properties of lateral and vertical silicon nanowires (SiNWs) were investigated using a conductive-probe atomic force microscopy (AFM). Horizontal SiNWs, which were synthesized by the in-plane solid-liquid-solid technique, are randomly deployed into an undoped hydrogenated amorphous silicon layer. Local current mapping shows that the wires have internal microstructures. The local current-voltage measurements on these horizontal wires reveal a power law behavior indicating several transport regimes based on space-charge limited conduction which can be assisted by traps in the high-bias regime (> 1 V). Vertical phosphorus-doped SiNWs were grown by chemical vapor deposition using a gold catalyst-driving vapor-liquid-solid process on higly n-type silicon substrates. The effect of phosphorus doping on the local contact resistance between the AFM tip and the SiNW was put in evidence, and the SiNWs resistivity was estimated

Emerging Tandem Solar Cells for Terrestrial Applications

International audiencePhotovoltaics has today become a mature industry and one of the main reasons of the tremendous growth in recent years is the continuous improvement in the performance and lifetime of PV modules. However, one of the main limitations in the improvement of the performance of commercialized PV devices is that the efficiency is getting closer and closer to the single-junction theoretical limit defined as the Shockley-Queisser (SQ) limit [1]. The development of new concepts to surpass the SQ limit is therefore a hot topic in PV research. Among the main candidate technologies (hot carriers, up-conversion and down-conversion, light concentration …), multijunction devices are the only concept which have surpassed the SQ limit by a wide margin. Multijuntion devices are therefore the most promising solution for industrialization in the near future, and the dominant multijunction design today is the tandem solar cell. In this presentation, after a description of the functional advantages of multijunction solar cells, we’ll review the current status of tandems. We’ll compare the different types of tandem cells according to design principles, and in particular subcell materials, and discuss the challenges to upscaling tandem PV. In particular, we’ll discuss recent advances in tandem cells with a Si bottom cell and examine perovskite/Si tandem cells with a recent record efficiency of 29.8%

Introduction to Tandem Solar Cells

International audiencePhotovoltaics has today become a mature industry and one of the main reasons of the tremendous growth in recent years is the continuous improvement in the performance and lifetime of PV modules. However, one of the main limitations in the improvement of the performance of commercialized PV devices is that the efficiency is getting closer and closer to the single-junction theoretical limit defined as the Shockley-Queisser (SQ) limit [1]. The development of new concepts to surpass the SQ limit is therefore a hot topic in PV research. Among the main candidate technologies (hot carriers, up-conversion and down-conversion, light concentration …), multijunction devices are the only concept which have surpassed the SQ limit by a wide margin. Multijuntion devices are therefore the most promising solution for industrialization in the near future, and the dominant multijunction design today is the tandem solar cell. In this presentation, after a description of the functional advantages of multijunction solar cells, we’ll review the current status of tandems. We’ll compare the different types of tandem cells according to design principles, and in particular subcell materials, and discuss the challenges to upscaling tandem PV. In particular, we’ll discuss recent advances in tandem cells with a Si bottom cell and examine perovskite/Si tandem cells with a recent record efficiency of 29.8% [2]. We will then present characterization techniques which allow the study of the electrical properties of tandem cells as a complete device, and of the properties of the subcells constituting the tandem

Technique du photocourant modulé pour la caractérisation des états localisés dans la bande interdite des semiconducteurs en couches minces

National audienc