Italian researchers from two Italian institutions have used graphene to develop a perovskite-silicon solar cell - a promising new solar technology - with an impressive conversion efficiency of 26.3%.
The researchers added graphene to the titanium dioxide electron selective layer used in a perovskite solar cell in order to increase chemical stability. The two-terminal cell was made by stacking two sub-cells which were fabricated and optimized separately. The new device blends the advantages of thin-film perovskite and silicon-based heterojunction cells, according to its developers.
The scientists added graphene to the titanium dioxide (TiO2) electron selective layer used in the perovskite cell to increase the chemical stability of the perovskite films and durability of the cell.
Graphene flakes were deposited on a titanium dioxide precursor and TiO2 nanoparticle solutions. Such a small amount of graphene flake doping has been demonstrated to be sufficient for boosting the photovoltaic performance of the mesoscopic [relating to dimensions ranging from nanoscale to micrometers] perovskite solar cells without altering the optical absorption of the whole device, the researchers stated.
The two-terminal cell was made by applying a ‘‘mechanical approach’’ to stack two sub-cells which were fabricated and optimized separately. The optimized, bifacial, mesoscopic, perovskite top cell has been mechanically stacked over a silicon bottom cell by applying a pressure of around 1kg/cm² over the contact area between the two sub-cells, the Italian group said.
The effective coupling of the two cells, the scientists said, ensured the resulting device had a high fill factor of 75.6%. Such optimized, bifacial, perovskite solar cells have been used as top cells in tandem devices adopting either double-side textured c-Si [crystalline silicon] and Si HJT [silicon heterojunction] bottom cells, reaching a champion PCE [power conversion efficiency] of 26.3% in reverse voltage scan mode (25.7% in forward voltage scan mode and stabilized PCE of 25.9%) over an active area of 1.43cm², the paper noted.
Research co-ordinator Mario Tucci added: Graphene improved performance in the perovskite cell while the heterojunction structure with amorphous films in the rear silicon cell allowed to increase the tension.