Rice University researchers 'dissolve' final roadblock in perovskite solar panels
Researchers at Rice University have solved the 'stability problem' of the solar panels made from halide perovskites paving the way for their commercial production and usage. In the research study published today, the researchers have detailed the right solvent that allows the building of 3D/2D solar cells with high energy conversion efficiency.
Perovskite solar cells hold massive potential since their energy conversion efficiencies have scaled up very quickly over the past decade. However, large-scale applications using perovskites solar cells are not common today since the material is extremely prone to decomposition when it comes in contact with moisture and oxygen.
Over the past few years, researchers have made improvements to the material and demonstrated survival for months. However, for commercial applications, perovskite solar cells need to remain stable for at least two decades. This could now be possible with the work done by researchers at Rice University.
Bifacial perovskite solar cells
Aditya Mohite, a chemical and biomolecular engineer, has a lab at the School of Engineering at the university where he conducts research in building thin 3D/2D solar cells.
In the press release, Mohite elaborates that 2D perovskites are stable but suffer from a lower efficiency of energy conversion while the 3D cells have higher energy conversion efficiency but low stability.
Combining these two types brings the best features of both to the fore. These bifacial cells can be used for applications where light comes in from both sides. The 2D perovskite absorbs blue and visible photos while the 3D side absorbs near-infrared ones.
However, manufacturing these cells is complicated. Industry-wide, solution processing is the method that is used for such applications, where material can be deposited on another by placing it in a liquid. When the liquid evaporates, the coating remains.
Since both layers in a bifacial cell are made up of the same material, solvents used in making them can dissolve the underlying layer too.
Finding the right solvent
Mohite's team looked at two important properties of the solvent, the dielectric constant and Gutmann donor number. The dielectric constant is the ratio of the electric permeability of the material to its free space. This determines how well a solvent can dissolve a compound. The donor number is the electron-donating capability of the solvent's molecules.
By studying these properties for perovskites, Mohite and his research team found that there were just four solvents that could dissolve perovskites and still process them without disrupting the lower layer, the press release said. The researchers tested the solar cells to light for over 2,000 hours but did not see even one percent degradation. The cell layers are just one micron thick.
Using their discovery, one could manufacture perovskites solar cells at a capacity of 30 meters per minute, Mohite claims. Interestingly, the applications are not limited to solar energy alone. The method also opens up areas like green hydrogen, non-grid solar for cars, and building integrated photovoltaics, the press release added.
The research findings were published today in the journal Science.
Realizing solution-processed heterostructures is a long-enduring challenge in halide perovskites because of solvent incompatibilities that disrupt the underlying layer. By leveraging the solvent dielectric constant and Gutmann donor number, we could grow phase-pure two-dimensional (2D) halide perovskite stacks of the desired composition, thickness, and bandgap onto 3D perovskites without dissolving the underlying substrate. Characterization reveals a 3D–2D transition region of 20 nanometers mainly determined by the roughness of the bottom 3D layer. Thickness dependence of the 2D perovskite layer reveals the anticipated trends for n-i-p and p-i-n architectures, which is consistent with band alignment and carrier transport limits for 2D perovskites. We measured a photovoltaic efficiency of 24.5%, with exceptional stability of T99 (time required to preserve 99% of initial photovoltaic efficiency) of >2000 hours, implying that the 3D/2D bilayer inherits the intrinsic durability of 2D perovskite without compromising efficiency.