Record performance for the Fraunhofer triple junction solar cell
(Rinnovabili.it) – The efficiency of perovskite/silicon tandem solar cells it quickly established itself as the new milestone in the sector, surpassing the performance of double junction cells based on III-V semiconductors (e.g. GaInP/GaAs). Thanks to yields above 30% they have inaugurated a new era for high efficiency and low cost photovoltaics. But above all they have opened the doors of multi-junction technology to perovskites.
The next step comes today from Fraunhofer Institute for Solar Energy Systems ISE where a research group created a Perovskite/perovskite/silicon triple junction solar cell with a open circuit voltage of more than 2.8 volts. An important result for the sector and also Triumph research project, funded by the European Commission. The initiative, of which Fraunhofer ISE is a partner, is working to create an advanced concept of monolithic triple junction cells with a conversion efficiency of over 33% and a size of over 100 square cm.
The open circuit voltage
To fully understand the progress achieved by the new triple junction solar cell it is necessary to take a few steps back. The performance of photovoltaic cells is determined by three main factors: open circuit voltage, short circuit current and fill factor. Among these, the first is the one most strongly influenced by the intrinsic properties of the materials used and indicates the maximum electrical voltage that the cell can provide in the absence of an electrical load. By comparison, traditional crystalline silicon units boast an open circuit voltage of between 0.7 and 0.8 volts.
The monolithic two-terminal, triple-junction solar cell created by the German Institute proves to be perfect for the job. “The voltage of more than 2.8 volts measured for the perovskite-perovskite-silicon solar cell suggests that the technology is extremely promising for electricity production“, says Dr Juliane Borchert, group leader for perovskite-silicon technologies at Fraunhofer ISE and at the University of Freiburg. “This is a record value for this type of solar cell and demonstrates how photovoltaics that combine perovskite and silicon offer enormous untapped potential”.
The result was achieved through a gas quenching method for the deposition of the upper layer of perovskite which allows a homogeneous formation of the absorber and prevents solvent damage to the underlying layers. The process also allowed the optimization of the intermediate interconnection layers between the perovskite subcells. The results of the study were published on ACS Energy Letters (English text).
