Materials and devices for photovoltaics (MIB-SOLAR)

Inorganic materials for solar energy

Currently, crystalline-Si (c-Si) based devices rule the photovoltaic (PV) market, accounting for about 96% of the total annual production versus 4% for thin films based technologies (namely, CdTe, Cu(In,Ga)Se2 (CIGS) and a-Si). In spite of the strong market gap between Si and thin films technologies, the development of PV absorbers proper for thin films based devices is nowadays even more crucial than in the past for future applications both in Building/Product Integrated Photovoltaics and in tandem devices. Furthermore, the availability of many raw materials used in thin film solar devices is seriously decreasing, while both energy and technology needs for the daily life are strongly increasing, which makes material saving crucial. The most studied alternatives to CdTe and CIGS in the last years were Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe), where more abundant and less expensive elements like Zn and Sn are used in place of In and Ga. More recently, further alternatives based on earth abundant elements emerged, among them Cu2MnSnS4 (CMTS) and Cu2FeSnS4 (CFTS).

Our research activities deal with the above-mentioned PV absorbers and related solar devices. In detail:

SILICON  Under the realistic assumption that c-Si based PV modules will dominate the PV market in the coming decade, our research activity has been focused on the further increase of Si solar cells efficiency (studying the effect of defects mainly by spectroscopic techniques), on the characterization of low price andhigh quality solar grade silicon feedstock and finally on new initiatives to build high efficiency tandem solar cells.

CIGS and CuGaS2 (CGS) thin films on glass and flexible substrates (like plastic foils) are grown by an innovative hybrid sputtering-evaporation approach (combining the advantages of both techniques) and tested both in single junction and tandem devices.

CZTS, CFTS and CMTS are prepared mainly by a soft-chemical route involving the coordination of the metals into the solution thanks to the use of DMSO as solvent and thiourea as sulphur source, making it very appealing due to the absence of further organic additives and external sulphur sources. The precursors solution is directly deposited by drop-casting onto the substrate without the use of further expensive and/or industrially non-compatible instruments, making the whole procedure appealing for industrial green application.

Lately, halide perovskite (HP) solar cells broke into thin film PV technology, proposing themselves as the best companion of silicon and chalcogenide-based thin films in tandem architecture devices. In this scenario, the HP range of light absorption can be tuned, varying the chemical composition, to match the requirements of the tandem counterpart. By varying the deposition method, along with the chemical composition, efficient semi-transparent solar cells can be made for use in smart windows. Besides, HPs can self-assemble in bulk materials where the charge is confined, for this reason, they are called low-dimensional HPs. The charge confinement impact on the optoelectronic properties opens the way for various HPs technology applications (e.g. thermoelectric generators, memristors and sensors).

A comprehensive structural and spectroscopic characterization (including scanning electron microscopy, Raman spectroscopy, X-ray diffraction and photoluminescence) is performed for all these compounds. All thin films are produced, tested and fully characterized in prototype devices on rigid and flexible substrates.

Research Lab

U5 Building, 1st Floor, Room 1032-1034-1037-1041
U5 Building, Ground Floor, Room T057-T067
U4 Building – Room 101
U9 Building – Room 10