Characterization of mono- and bifacially active semitransparent crystalline silicon solar cells under out-door operating conditions

The novel POWER (Polycrystalline Wafer Engineering Result) solar cell concept (Willeke et al., 1994) possesses interesting properties for the photovoltaic market. An optical semitransparency of up to 20% can be combined with a bifacial light-collecting activity. POWER cells have been characterized under standard test condition (STC) (Kuhn et al., 1998). Latest results show efficiencies of 12.7% for bifacial POWER cells with 11% optical transmittance and 11.2% for monofacial POWER cells with 18% transmittance (both on Cz-Si), best efficiencies on mc-Si are 12.0% respectively 10.0%. However, due to its semitransparency and bifacial activity this cell type is very sensitive to background reflections as well as to diffuse irradiation. These two parameters are not easy to control in STC-characterization. This paper presents IV-measurements of POWER solar cells under actual operating conditions. Mono- as well as bifacially active semitransparent solar cells have been characterized using natural sunlight on a specialised outdoor test facility (Durisch et al., 1998) and are compared to conventional solar cells. The results are in good agreement with the STC-measurements. The influence of different angles of irradiation and different types of background reflectors on the IV-characteristic has been investigated for fixed as well as for suntracked positioning.