CHEOPS assessed a new production process for bigger (5x5 cm2) perovskite solar cells. The process significantly improves the cells’ performance and spatial uniformity – both is key to the scale-up of the technology.
To increase the photovoltaic performance of perovskite solar cells, CHEOPS researchers conducted several experiments to assess the effect of a thinner electron transporting layer (compact titanium dioxide blocking layer, BL-TiO2) on photovoltaic parameters of perovskite solar cells.
Results show that, in this case, less is more:
Reducing the thickness of BL-TiO2 from 40-50 nm to 20-30 nm increased the open circuit voltage by 10.36 % on average. The fill factor was increased by an average of 3.79 % (absolute increase). The picture below shows a cross-sectional scanning electron microscope (SEM) image of the optimized device stack.
Perovskite depositions are very sensitive to the realization technique, the curing and the annealing steps, which means that what works for the production of lab-scale cells may not work for larger cells. This is why, in addition to photovoltaic performance, spatial uniformity is key for the scale-up of perovskite technology and characterization of the perovskite homogeneity is mandatory. CHEOPS researchers did so by using light beam induced current (LBIC) measurements to assess the homogeneity of 5x5 cm2 modules, produced with three different coating techniques: Two-step blade-coating, anti-solvent quenching and spin-coating. As the LBIC map below indicates, modules fabricated by using the two-step procedure and the automated blade coater (for both perovskite and hole transport layer) are the most uniform. Blade coating also allows production in air without controlling the environment and facilitates scale-up to larger substrates.
Spin-coated perovskite, spin-coated Spiro-OMeTAD
Blade-coated perovskite, spin-coated Spiro-OMeTAD
Blade-coated perovskite, blade-coated Spiro-OMeTAD
CHEOPS will continue to optimize photovoltaic performance by improving the perovskite formulation passing from methylammonium-based perovskite to mixed-cation perovskites with optimized morphologies and thickness. This formulation will be applied to a larger substrate (10x10 cm2) which comes closer to the size required for industrial production.
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