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The selective emitter formation by laser doping is a well known process to increase the efficiency of silicon solar cells [1] , [2] . For the characterization of laser doped emitters, SIMS (Secondary Ion Mass Spectroscopy) and ECV (Electrochemical Capacitance Voltage Measurement) techniques are used to analyze the emitter profile [3] . It is very difficult to get acceptable result by SIMS on a textured surface, so only ECV can be used. It has been shown, that a charge carrier depth profile can be measured on a homogeneous emitter only by ECV. The use of laser doping results in a non-homogeneous emitter. We have shown that the emitter depth is not just a function of the pulse power, but in addition of the surface structure of the wafer. The texture seems responsible for a strong variability in the doping profile. It has been shown, that the ECV measurement is not applicable to characterize the emitter depth on laser doped areas, because of the microscopic inhomogeneities in the emitter on the macroscopic measurement area. The real emitter profiles are to complex to be characterized by SIMS or ECV. We have shown that the variation in the emitter profile is resulting from the texture in the laser-doped regions.

The growth of highly conductive boron doped microcrystalline silicon by the hot wire method was studied. Various series of films were deposited to investigate the influence of the deposition parameters on conductivity, crystallinity and (void-related) microstructure. Maximum (room temperature) conductivities > 200 S/cm with carrier mobilities > 2.5 cm2/Vs were achieved. While a high crystallinity is the major requirement for achieving high conductivities, the microstructure is also of influence. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this paper, we report on tire outcome of a German network project conducted with 12 partners from universities and research institutes on the material development of dye solar cells (DSC). We give an overview in the field and evaluate the concept of monolithic DSC further with respect to upscaling and producibility oil glass substrates. We have developed a manufacturing process for monolithic DSC modules which is entirely based on screen printing. Similar to our previous experience gained in the sealing of standard DSC, the encapsulation of the modules is achieved in a fusing step by soldering of glass frit layers. For use in monolithic DSC, a platinum free, conductive counter electrode layer, showing a charge transfer resistance of R-CT

Hydrogenated amorphous silicon carbide (a-SiC:H) provides excellent electronic surface passivation for crystalline silicon solar cells. The hydrogen and carbon content of the passivation layers control the surface passivation depending on hydrogen bonding and annealing temperature. The carbon content c C of the amorphous layers varies depending on the methan-to-silane gas flow ratio during deposition. The electronic passivation quality exhibits best thermal stability for an optimum c C = 2.3 at.%. Annealing this sample under forming gas atmosphere up to T FG = 550°C enables excellent effective minority carrier lifetimes τ eff = 1.2 ms. Hydrogen effusion measurements relate this result to an increase in H-content with rising c C and to a simultaneous shift of the effusion peaks to higher temperatures. A higher carbon content reduces the diffusion of atomic hydrogen out of the amorphous layers. The Si-H bonding configurations in the amorphous layers, analyzed from infrared absorption spectroscopy, reveal that a-SiC:H layers with lower carbon content have a higher density. Increasing c C induces voids and microvoids in the amorphous structure, favoring the diffusion of molecular hydrogen out of the a-SiC:H layers. We show the implementation of the thermally most stable a-SiC:H as back side of an industrial silicon solar cell. Evaporated and tempered Al point contacts through the amorphous layers enable the current transport through a-SiC:H. Compared to a full-area back side metallization, the lower recombination velocity of the a-SiC:H back side enhances the open circuit voltage, demonstrating the benefit of a-SiC:H passivation for industrial crystalline silicon solar cells.

The characterization of void-related microstructure in amorphous and microcrystalline Ge:H films is reported. Various methods are applied including effusion measurements of hydrogen and of implanted helium and neon, measurements of the infrared absorption of C-H bonds due to in-diffusion of contaminants and of the stretching modes of bonded hydrogen. Several microstructure effects like interconnected voids and isolated voids and a quite different material homogeneity are detected and are found to depend on the preparation conditions. Amorphous Ge:H can be prepared with a (largely) homogeneous structure while microcrystalline Ge:H tends to consist of compact grains surrounded by more or less open voids. Enhanced substrate temperatures (Ts ≈ 250°C) favour the growth of more compact material.

We study resistive losses at (p)c-Si/(p)Si:H/(n)ZnO heterojunction back contacts for high efficiency silicon solar cells. We find that a low tunnelling resistance for the (p)a-Si:H/(n)ZnO part of the junction requires deposition of Si:H with a high hydrogen dilution RH > 40 resulting in a highly doped μc-Si:H layer. Such a μc-Si:H layer if deposited directly on a Si wafer yields a surface recombination velocity of S  180 cm/s. Using the same layer as part of a (p)c-Si/(p)Si:H/(n)ZnO back contact in a solar cell results in an open circuit voltage Voc = 640 mV and a fill factor FF = 80 %. Insertion of an (i)a-Si-layer between the μc-Si:H and the wafer leads to a further decrease of S and, for the solar cells to an increase of VOC. However, if the thickness of this intrinsic layer exceeds a threshold of 3 nm, resistive losses lead to a degradation of the fill factor of the solar cells. These resistive losses result from a valence band offset δEV between a-Si:H and c-Si of about 600 meV. The fill factor losses overcompensate the VOC gain such that there is no benefit of the (i)a-Si:H interlayer for the overall solar cell performance when using an (i)a-Si:H/(p)uc-Si:H double layer.

A cost effective glass soldering technique was developed which has been successfully applied to the dye solar cell (DSC) technology. A complete manufacturing process of DSC modules ? ranging from screen-printed layers to semi-automated colouring and electrolyte filling ? in a laboratory-scale baseline has been accomplished. The manufacturing process of 30 × 30 cm2 modules was partly transferred to large areas of 60 × 100 cm2. Electrolytes based on non-volatile organic ionic liquids have been tested as good candidates for long-term stability and performance. By screen printing a light scattering ZrO2 layer over the transparent active area of the module, various different patterns ? ranging from logo-type to image-type designs ? were realised. Additionally, the lead-free glass frit was coloured by inorganic pigments to adjust the unique esthetical appearance of the module.

Thermal stability of passivating layers in amorphous/crystalline silicon (a-Si/c-Si) heterojunction solar cells is crucial for industrial processing and long-term device stability. Hydrogenated amorphous silicon (a-Si:H) yields outstanding surface passivation as atomic hydrogen saturates silicon dangling bonds at the a-Si/c-Si interface. Yet, a-Si surface passivation typically starts to degrade already at annealing temperatures in the range of 200 to 250 °C depending on annealing time, and optical absorption in front layers of a-Si reduces the short circuit current density. We show that oxygen incorporation into a-Si:H films enhances the thermal stability of the passivation and reduces parasitic absorption. We further show that for good passivation of the a-Si/c-Si interface, a compact material structure of the a-Si:O:H films is required where atomic hydrogen is the dominating type of diffusing hydrogen species. For plasma deposited a-Si:O:H films, oxygen incorporation of up to 10 at. % leads to an increa...

We investigate resistive losses at p-type crystalline Si/hydrogen passivated Si:H/ZnO:Al heterojunction back contacts for high efficiency silicon solar cells. A low tunneling resistance for the (p-type) Si:H/(n-type) ZnO part of the junction requires deposition of Si:H with a high hydrogen dilution rate R-H>40 resulting in a highly doped microcrystalline (mu c) Si:H layer. Such a mu c-Si:H layer if deposited directly on a Si wafer yields a surface recombination velocity of S approximate to 180 cm/s. Using the same layer as part of a (p-type) c-Si/Si:H/ZnO:Al back contact in a solar cell results in an open circuit voltage V-OC=640 mV and a fill factor FF=80%. Insertion of an undoped amorphous (i) a-Si:H layer between the mu c-Si:H and the wafer leads to a further decrease of S and, for the solar cells, to an increase of V-OC. However, if the thickness of this intrinsic layer exceeds a threshold value of 4-5 nm, resistive losses degrade the fill factor FF of the solar cells. Temperature dependent measurements of the contact resistance unveil activation energies in a range of 0.49-0.65 eV, which we attribute to the valence band offset between a-Si:H and c-Si. The balance of FF losses and V-OC gains determines the optimum (i) a-Si:H interlayer thickness for (i) a-Si:H/(p) mu c-Si:H double layer or (i) a-Si:H/(p) a-Si:H/(p) mu c-Si:H triple layer back contacts.(C) 2007 American Institute of Physics.

This paper examines the thermodynamic limits of photovoltaic solar energy conversion by fluorescent collectors. The maximum efficiency of a fluorescent collector corresponds to the Shockley–Queisser limit for a nonconcentrating solar cell with a single bandgap energy. To achieve this efficiency, the collector requires a photonic structure at its surface that acts as an omnidirectional spectral band stop filter. The large potential of photonic structures for the efficiency enhancement of idealized as well as real fluorescent collectors is highlighted.