The Lower Saxony Institute for Solar Energy Research Hameln (ISFH), an institute of the Leibniz University of Hanover, has achieved a solar cell efficiency of 25.0% in cooperation with the Institute for Materials and Devices of Electronics (MBE) of Leibniz Universität Hannover. This result was confirmed by the DAkkS-accredited independent calibration laboratory ISFH-CalTeC and reported at the Asian conference PVSEC-26 in Singapore.
This high efficiency was achieved with passivating POLO contacts for both polarities, which avoid the otherwise high recombination among the metal contacts. POLO stands for ” pol y-Si on o oxides”.
The contacts consist of a thin silicon oxide and a doped polycrystalline silicon layer. Due to the POLO contacts the recombination could be reduced so much that a high open clamping voltage of 723 mV was achieved. Both polarities of the POLO layers are located on the back of the solar cell, which avoids the shadowing of the front by metal fingers and reduces parasitic absorption in the poly-Si. The result was on a cell area of 3.97 cm 2 obtained (designated area). In the ongoing project the efficiency is to be further increased and complex laboratory processes should be replaced by industrially relevant processes. The work was carried out within the framework of a collaborative project (FKZ: 0325827A) sponsored by the German Federal Ministry of Economics and Energy (BMWi), in which the ISFH, the MBE and the Fraunhofer Institute for Solar Energy Systems (ISE) cooperate.