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An overview of the high-efficiency solar cell developments with crystalline silicon at Fraunhofer ISE (Germany) is given. Seven types of solar cells are discussed: (1) LBSF cells (local back surface field); (2) RP-PERL cells (random pyramids, passivated emitter rear locally-diffused); (3) RP-PERC (random pyramids, passivated emitter and rear cell); (4) MESC (mesh-structured emitter cell): (5) cells with interdigitated contacts; (6) high-efficiency thin film solar cells based on SOI (silicon on insulator); and (7) mini modules integrated on one 4" SOI-wafer. All these cells show very good efficiencies close to or well above 20%, respectively. The goal of all activities is to develop technologies for efficiencies as high as possible but at the same time as simple as possible. Many of the developments are performed in close cooperation with German PV companies and/or with European research teams in the framework of projects of the European Commission.

The characterization of two types of silicon solar cells with interdigitated metal grids processed at Fraunhofer-ISE is presented in this paper: the 19.2% efficient thin-film silicon on insulator (SOI) cell and a 21.4% rear contact cell (RCC). The spectrally resolved reflection and absorption properties of the cells are simulated with the 3D ray tracing program RAYN. Optical generation profiles calculated with RAYN are utilized in the device simulator DESSIS to model the observed electrical properties. The successful modelling allows predictions of the performance of thinner SOI cells and RCC cells processed from lower quality material.