The effect of silicon and copper-indium-gallium-selenide based solar cell structures and processing on temperature dependent performance losses
University of Delaware
Temperature dependent current voltage measurements (J-V-T) of solar cells provide both fundamental and practical information. They give detailed insight into recombination losses within the device as well as information about module performance losses at higher outdoor operating temperatures. In this thesis, J-V-T measurements were applied to two distinctly different types of solar cells: crystalline silicon heterojunction cells and thin film (AgCu)(InGa)Se2 or ACIGS polycrystalline cells. Crystalline silicon solar cells with heterojunction structure improve the opencircuit voltage and efficiency. Interdigitated back contact (IBC) Si solar cells obtain a higher short-circuit current and fill factor compared to front heterojunction (FHJ) solar cells. ACIGS solar cells have shown higher efficiencies at wider bandgap compared to the baseline CIGS solar cells. Two high open-circuit voltage CIGS solar cells are included and compared with ACIGS solar cells. In this thesis, the impact of different types of solar cells structure and fabrication on temperature dependent performance losses will be discussed. Devices with higher bandgap are predicted to have higher open-circuit voltage and lower temperature coefficient of maximum power output (Pmax). The correlation between temperature coefficient of Pmax and open-circuit voltage can be found in Si FHJ cells but not Si IBC or ACIGS cells. However, ACIGS cells show an inverse correlation between temperature coefficient of Pmax and bandgap as expected. Analysis of diode quality factor and other parameters are interpreted. Sshape J-V curve can reduce the device's fill factor with a relative high series resistance. This phenomenon tends to occur in FHJ cells rather than IBC at low temperature. Light-dark crossover and roll over effects are commonly seen in ACIGS cells and the anomaly is enhanced at lower temperature. Most of FHJ and IBC cells obtain the ideality factor between 1 and 2 while some of ACIGS cells obtain the ideality factor less than 1 or larger than 2. The value of the ideality factor may be limited by different recombination mechanism.