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In amorphous/crystalline silicon heterojunction solar cells, optical losses can be mitigated by replacing the amorphous silicon films by wider bandgap amorphous silicon oxide layers. In this article, we use stacks of intrinsic amorphous silicon and amorphous silicon oxide as front intrinsic buffer layers and show that this increases the short-circuit current density by up to 0.43 mA/cm² due to less reflection and a higher transparency at short wavelengths. Additionally, high open-circuit voltages can be maintained, thanks to good interface passivation. However, we find that the gain in current is more than offset by losses in fill factor. Aided by device simulations, we link these losses to impeded carrier collection fundamentally caused by the increased valence band offset at the amorphous/crystalline interface. Despite this, carrier extraction can be improved by raising the temperature; we find that cells with amorphous silicon oxide window layers show an even lower temperature coefficient than reference heterojunction solar cells (-0.1%/°C relative drop in efficiency, compared to -0.3%/°C). Hence, even though cells with oxide layers do not outperform cells with the standard design at room temperature, at higher temperatures--which are closer to the real working conditions encountered in the field--they show superior performance in both experiment and simulation. [ABSTRACT FROM AUTHOR]

While p-n junction solar cells have long been established as the dominant solar-cell technology in the market, the origin of the charge-carrier separation in these devices remains open to debate. It is often attributed to the built-in electric field that exists across the junction in thermodynamic equilibrium, although this interpretation can lead to physical inconsistencies. In this work we present an interpretation approach based on the analogy between a solar cell and a generalized electric source model. Our interpretation is given through a detailed analysis of the electric potential and the non-electric chemical potential across each device, which are plotted together in complete potential diagrams introduced for this purpose. We demonstrate that the driving force separating the free charge carriers in both devices originates from the change of the non-electric chemical voltage that happens once the device is brought out of thermodynamic equilibrium. This change, therefore, can be interpreted as the driving force that triggers the selective motion of charge carriers and, thus, induces the electric voltage at the terminals of the device. [ABSTRACT FROM AUTHOR]

Provides information on a study examination the function of a thin microcrystalline p(...c-SiH) layer in a p-i-n hydrogenated amorphous silicon (a-Si:H) based solar cell. Methodology used to conduct the study; Information on circumstances at the ZNO/p front contact heterozygosity; Detailed information on the examination of p(...c-Si:H) fundamental material parameters; Conclusions reached on the study.

Examines the band-gap engineering in CdS/Cu(In,Ga)Se[sub2] (CIGS) solar cells using a numerical device simulation program. Simulation model description; Discussion on band-gap engineering in CIGS base structure; Analysis of two grading concepts.

Calculates the transient response after turning the light off. Simulation of transient phenomena in amorphous silicon devices; Fitting of two families of measured steady-state characteristics such as light intensity and temperature dependence of the secondary photocurrent.

In amorphous/crystalline silicon heterojunction solar cells, an inversion layer is present at the front interface. By combining numerical simulations and experiments, we examine the contribution of the inversion layer to lateral transport and assess whether this layer can be exploited to replace the front transparent conductive oxide (TCO) in devices. For this, heterojunction solar cells of different areas (2 × 2, 4 × 4, and 6 × 6 mm2) with and without TCO layers on the front side were prepared. Laser-beam-induced current measurements are compared with simulation results from the ASPIN2 semiconductor simulator. Current collection is constant across millimeter distances for cells with TCO; however, carriers traveling more than a few hundred microns in cells without TCO recombine before they can be collected. Simulations show that increasing the valence band offset increases the concentration of holes under the surface of n-type crystalline silicon, which increases the conductivity of the inversion layer. Unfortunately, this also impedes transport across the barrier to the emitter. We conclude that the lateral conductivity of the inversion layer may not suffice to fully replace the front TCO in heterojunction devices. [ABSTRACT FROM AUTHOR]

Silicon heterojunction solar cells have record-high open-circuit voltages but suffer from reduced short-circuit currents due in large part to parasitic absorption in the amorphous silicon, transparent conductive oxide (TCO), and metal layers. We previously identified and quantified visible and ultraviolet parasitic absorption in heterojunctions; here, we extend the analysis to infrared light in heterojunction solar cells with efficiencies exceeding 20%. An extensive experimental investigation of the TCO layers indicates that the rear layer serves as a crucial electrical contact between amorphous silicon and the metal reflector. If very transparent and at least 150 nm thick, the rear TCO layer also maximizes infrared response. An optical model that combines a ray-tracing algorithm and a thin-film simulator reveals why: parallel-polarized light arriving at the rear surface at oblique incidence excites surface plasmons in the metal reflector, and this parasitic absorption in the metal can exceed the absorption in the TCO layer itself. Thick TCO layers-or dielectric layers, in rear-passivated diffused-junction silicon solar cells-reduce the penetration of the evanescent waves to the metal, thereby increasing internal reflectance at the rear surface. With an optimized rear TCO layer, the front TCO dominates the infrared losses in heterojunction solar cells. As its thickness and carrier density are constrained by anti-reflection and lateral conduction requirements, the front TCO can be improved only by increasing its electron mobility. Cell results attest to the power of TCO optimization: With a high-mobility front TCO and a 150-nm-thick, highly transparent rear ITO layer, we recently reported a 4-cm2 silicon heterojunction solar cell with an active-area short-circuit current density of nearly 39 mA/cm2 and a certified efficiency of over 22%. [ABSTRACT FROM AUTHOR]