Cheap materials and new techniques

A significant reason for the high cost price of solar cells is the high purity of the semi-conductive materials required for being able to separate well the charges that occur from the sunlight. TU Delft has been able to demonstrate that if the active zones in the solar cell are made from very small particles (nano-composites) that charge separation comes about faster, so that in the future it becomes possible to apply less costly materials of lesser purity (like titanium oxide – TiO₂, an ingredient of toothpaste and latex). TU Delft is also studying nano-structuring in order to increase the output of silicon based thin layer solar cells.

Thin film silicon solar cells are considerably more environmentally-friendly and less costly than the current crystalline solar cells. These cells are very thin - the thickness of the silicon layer is about 200 to 300 times thinner than the thickness of the crystalline silicon of the first generation of solar cells - and are produced at low temperature, so the expectation is that in large-scale production these solar cells will become less costly than the crystalline silicon solar cells. In the years to come they will be acquiring a substantial market share. TU Delft is studying possibilities for improving and accelerating the production technology of the thin films (with the so-called chemical vapour deposition (CVD) technique), thereby simultaneously increasing the conversion efficiency. In this the university is working closely with industry (Nuon’s subsidiary Helianthos), and other research institutes (University of Utrecht, Eindhoven University of Technology, ECN, TNO-TPD). Among other things this collaboration has resulted in a new, promising production process that Nuon will soon be taking into use. TU Delft has some advanced infrastructure for making and characterising thin film silicon trial cells.

Light absorption with which free charges are produced is the first step in the electricity production process in the solar cell. In principle, no costly materials are necessary for this. Organic materials (plastics) are of considerable interest for this. In a few cases, these materials are being combined with metal oxides like titanium oxide in order to attain efficient charge separation. Fundamental research is being used to explain the relationship between material composition and free charging as a result of light absorption. Examples of the materials being studied are conjugated polymers, PCBM and porphyrins.