Breakthrough towards cheap and efficient solar cells

Scientists from EPFL and CSEM have made remarkable progress in the photovoltaics field, specifically in perovskite-on-silicon tandem solar cells, by achieving an impressive efficiency of 31.25%. This noteworthy accomplishment is a result of advancements in materials and processes that have successfully unlocked the true potential of this emerging technology. Studies at NCD-SWEET beamline of ALBA have been carried out to analyse these materials. The scientific breakthrough behind this milestone has been published in Science, representing a significant step towards a greener, cleaner energy future and the ongoing energy transition.

Cerdanyola del Vallès, 4th October 2023 Silicon solar cells that are commonly used for solar electricity generation are limited in terms of efficiency — the amount of sunlight that hits a solar cell and gets converted into electricity. The current highest efficiency records for silicon-only solar cells stand around 24.5% for commercial cells and 27% in laboratory settings. These figures are considered close to the theoretical maximum of 29% for such cells, with little progress in moving this number higher in recent years. Research groups worldwide are engaged in efforts to enhance the efficiency and develop innovative materials, like metal halide perovskites, as potential alternatives to silicon.

Racing past crucial energy barrier

To overcome this efficiency limitation and further reduce the costs of solar electricity, scientists from EPFL’s PV-Lab and CSEM have been exploring innovative approaches and finally demonstrated, in the article published in Science,an efficiency of 31.25% by stacking silicon and perovskite cells in a so-called tandem structure. This achievement marks the first time a low-cost technology has surpassed the 30% efficiency milestone.

Tandem solar cells offer improved utilization of solar energy by optimizing each sub-cell to capture different parts of the solar spectrum. However, typical limitation of perovskite-on-silicon tandem cells is the recombination losses that occur at the perovskite interface with the electron selective contact. Recombination refers to the loss of photogenerated charge carriers before they can be collected and utilized to generate electricity.

To address this issue, EPFL’s and CSEM’s scientists started with a standard commercial silicon cell and incorporated an additive in the processing sequence when growing the perovskite crystal on top. This additive effectively regulated the perovskite crystallization process and passivated the perovskite top interface. Passivation involves adapting the structure and chemistry of interfaces and surfaces so that energy loss is minimized, and a maximum of the energy generated can be utilized efficiently.

A bright light for a brighter energy future

In order to deeply analyse the impact of the additive on the perovskite crystallization process, grazing incidence wide-angle x-ray scattering (GIWAXS) was performed at the ALBA Synchrotron. “GIWAXS provides detailed information about the crystallographic structure, orientation, and phase transitions within the material”, explains Eduardo Solano, beamline scientist at ALBA. In particular, Solano gives support to research groups who come to ALBA for using this synchrotron light-based technique at NCD-SWEETa flexible dynamic multipurpose beamline that can accommodate a large variety of sample environments for in situ experiments.

Read more on ALBA website

Image: From left to right, Julian Steele, scientist at KU Leuven and at the University of Queensland, and Eduardo Solano, beamline scientist at NCD-SWEET.