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-cm 2 silicon heterojunction solar cell with an active-area short-circuit current density of nearly 39 mA/cm 2 and a certified efficiency of over 22%. V C 2013 American Institute of Physics. [http://dx

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In this article we determine descriptive scattering parameters—haze and angular distribution functions—of scattered light for textured glass/SnO2 Asahi U-type substrates. These scattering parameters are input parameters of our optical model that enables us to analyze multilayer optical systems with rough interfaces. The scalar scattering theory is used to calculate the haze parameters of all internal rough interfaces in the a-Si:H solar cells deposited on the glass/SnO2 substrates. In the equations of the scalar scattering theory the correction functions are introduced in order to match the calculations with the measurements of the haze parameters of the substrates. The angular distribution functions of the substrates are applied to the rough internal interfaces. Using these scattering parameters we investigate the optical behavior of a-Si:H solar cells with different intrinsic layer thicknesses deposited on the textured glass/SnO2 substrates with different roughnesses.