We present a detailed study on the rear contact formation of rear-surface-passivated silicon solar cells by full-area screen printing and alloying of aluminum pastes on the locally opened passivation layer. We demonstrate that applying conventional Al pastes exhibits two main problems: 1) high contact depths leading to an enlargement of the contact area and 2) low thicknesses of the Al-doped p + Si regions in the contact points resulting in poor electron shielding. We show that this inadequate contact formation can be directly linked to the deficiently low percentage of silicon that dissolves into the Al-Si melt during alloying. Thus, by intentionally adding silicon to the Al paste, we could significantly improve the contact geometry by reducing the contact depth and enlarging the Al-p + thickness in the contact points, enabling a simple industrially feasible way for the rear contact formation of silicon solar cells.Index Terms-Aluminum alloying, local back surface field, local emitter, silicon solar cells.

This paper discusses the influence of different solar cell loss mechanisms at low light intensities and presents a simple method for the analysis of solar cell performance under various illumination intensities below 1 sun. Suns-PL and Suns − V o c are used to measure the intensity-dependent pseudo I-V curves of symmetric test structures and of finished silicon solar cells in an intensity range between 1 sun and 10 −3 suns. The solar cell parameters from the pseudo I-V curves are compared with the parameters evaluated by intensity-dependent measurements of the whole I-V curve. The pseudo efficiency and pseudo fill factor are found to be in good agreement with the real values at low intensities as the influence of the series resistance vanishes. Based on this finding, we compare the passivation quality of silicon dioxide and silicon nitride in combination with emitter windows on test structures. Above 0.1 suns, both passivation layers show similar performance. Below 0.1 suns, the pseudo fill factors and pseudo efficiencies of the silicon nitride passivated sample are strongly reduced compared with the sample with silicon dioxide. The open-circuit voltage starts differing below 0.01 suns. Index Terms-Emitter windows, intensity dependence, low light intensities, pseudo I-V curve, suns-PL, suns-V o c .

No abstract

No abstract

Photovoltaic micro energy harvesting for self-sufficient sensor system applications is a promising new market for silicon photovoltaics. Therefore, silicon solar cells need to work under weak light conditions both outdoors, e.g. in the forest, or indoors. Hence, the spectral distribution of the given conditions differs as well with the application. We present a new investigation of real conditions and a first evaluation for a frequently used office. Even during winter the contribution of the artificial light sources does not exceed 35%. The spectrum is mainly determined by sun light. In order to proof the feasibility of solar cells for micro energy harvesting simulations of the efficiency limits for different spectra and intensities were made. The simulation of the theoretical efficiency limits show that silicon, which is best suited for AM1.5, can achieve even higher efficiencies for artificial light sources. Concerning the technological feasibility, PC1D simulation show that a PERC structure can be optimized resulting in efficiencies of 20% at an intensity of 1 sun and still 14% at an intensity of 1/1000 sun. The efficiencies even rise for artificial spectra of energy saving lamps, halogen bulbs or LEDs