A new perovksite solar cell successfully generates more than 23% efficiency

And it can be boosted to 30 percent.
Derya Ozdemir
A perovskite solar cell and people admiring solar energy system1, 2

A perovskite solar cell (PSC) with a unique passivation technique based on the utilization of guanidinium (Gua) and octylammonium (Oa) spacer cations has entered the solar scene; thanks to a team of researchers from Flinders University, the University of New South Wales, and Australian National University.

In case you missed it, perovskite solar cells are thin-film devices made up of layers of materials that are either printed or coated with liquid inks or vacuum-deposited. They offer a lot of potential advantages as they are extremely lightweight and can be made with flexible plastic substrates.

In their study, which was published in the journal Solar RRL, the researchers found that the guanidinium salts can improve the performance of the perovskite film.

This is of utmost importance as perovskite solar cells are not currently commercially viable because of their limited operational lifetimes. With numerous studies in the pipeline on understanding the stability and degradation of PSCs, this research takes us one tiny step closer to a mainstream solar power generation utilizing perovskite solar cells.

Engineering the chemistry 

Guanidinium salts were able to increase the performance of the perovskite film because guanidinium ions can penetrate the bulk of the perovskite material and localize at grain boundaries (GBs), according to an initial report from PV Magazine.

The researchers utilized guanidinium bromide (GuaBr) and octylammonium bromide (OABr) as cations. They are said to exceed their monospace cation counterparts in terms of short-circuit current density, power conversion efficiency, and thermal stability. The passivation layers were implanted on the hole transport layer (HTL) side.

"To optimize the ratio between GuaBr and OABr components, three different volume ratios of 1:1 (termed as 1G-1O), 1:2 (named as 1G-2O), and 2:1 (referred to as 2G-1O) were examined,” the team said in an interview with PV Magazine. “After spin coating the 3D perovskite precursor solution on the substrate and annealing it on a hotplate at 100 C for 30 minutes, the passivation solution is spun on the substrate, followed by another annealing at 100 C for 10 minutes."

Future of PSC shines a little brighter

As a result, the efficiency increased from 21.37 percent for the control cell to 23.13 percent for the passivated device, with significantly better shelf-life stability. Furthermore, the researchers reported that test device 1G-1O maintained approximately 97 percent of its initial efficiency after 60 hours of light soaking stability.

“We designed the cells to be used in small-scale residential solar systems or large-scale solar power plants,” researcher at The Duong explained to PV Magazine. “Significantly, the perovskite solar cell technology can be combined with the existing silicon solar cell technology in a tandem configuration to achieve ultrahigh efficiency of up to 30%.”

That's a significant number, and according to the researchers, further improvements in cell performance and stability may be possible by investigating other combinations. There are still a number of challenges before perovskite solar cells can become a competitive commercial technology; however, this is a step in that direction. With perovskite solar cells, which have been dubbed "the holy grail of solar" in many cases, becoming low-cost and gaining high efficiency, they can help increase solar adoption worldwide and pave the way for durable photovoltaics in the future.

Study Abstract:

One of the important factors in the performance of perovskite solar cells (PSCs) is effective defect passivation. Dimensional engineering technique is a promising method to efficiently passivate non-radiative recombination pathways in the bulk and surface of PSCs. Herein, a passivation approach for the perovskite/hole transport layer interface is presented, using a mixture of guanidinium and n-octylammonium cations introduced via GuaBr and n-OABr. The dual-cation passivation layer can provide an open-circuit voltage of 1.21 V with a power conversion efficiency of 23.13%, which is superior to their single cation counterparts. The mixed-cation passivation layer forms a 1D/2D perovskite film on top of 3D perovskite, leading to a more hydrophobic and smoother surface than the uncoated film. A smooth surface can diminish non-radiative recombination and enhance charge extraction at the interface making a better contact with the transport layer, resulting in improved short-circuit current. In addition, space charge-limited current measurements show a three times reduction in the trap-filled limit voltage in the mixed-cation passivated sample compared with unpassivated cells, indicating fewer trapped states. The shelf-life stability test in ambient atmosphere with 60% relative humidity as well as light-soaking stability reveal the highest stability for the dual-cation surface passivation. 

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