In this paper, the theoretical efficiency of multi‐junction solar cells based on group IV elements has been investigated. The effects of different absorbing layer numbers, different band gap combinations, and temperature changes have been reviewed for multi‐spectral solar cells. Several simulations were done to identify the ideal band gap combination for triple‐junction solar cells. Based on these results and under consideration of actual material parameters, a new promising triple‐junction solar cell concept with a‐Si:H/µc‐Si:H/ and µc‐Ge:H has been found for developing high efficiency thin film solar cells. Additionally, advanced simulations were performed in order to evaluate the feasibility of this new concept. The photocurrent, the external quantum efficiency, and the layer thicknesses were simulated and evaluated. All parameters deliver promising results for a new triple‐junction solar cell concept with an intermediate reflector between the middle‐ and bottom structure. Copyright © 2011 John Wiley & Sons, Ltd.

Solar cells used in building integration of photovoltaic cells (BIPV) are commonly made from crystalline wafer cells. This contribution investigates the challenges and benefits of using bifacial solar cells in vertical installations. We show that those cells get up to 13% more irradiance compared to optimum tilted south facing monofacial modules in Germany. The role of the n-layer in thin amorphous bifacial single-junction cells intended to be used as bifacial cells in BIPV applications is investigated. In contrast to the superstrate cell design, a transparent n-layer and back contact play a key role to achieve high bifaciality. We therefore increased the transparency of the n-layer by adding CO 2 , increasing the PH 3 flow in the deposition gas and tested different thicknesses. With those measures, we reached a bifaciality of 98% for short-circuit current density and 99% for open-circuit voltage. 184

Optical emission measurements were recorded during microcrystalline germanium layer growth on glass with plasma enhanced chemical vapor deposition. A significant difference for the intensities of SiH and GeH could be identified in the optical emission spectra of hydrogen/silane (H2/SiH4) and hydrogen/germane (H2/GeH4) plasma. In H2/SiH4 plasma, Si and SiH are present, whereas Ge but no GeH could be detected in H2/GeH4 plasma. The specific Raman crystallinity factor (ϕc) was evaluated for the layers after deposition. In H2/GeH4 plasma, the ratio of optical emission intensities of Hα (I(Hα), λ = 656.28 nm) and Ge (I(Ge), λ = 303.90 nm) is proportional to ϕc,Ge.

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