Perovskite solar cells (PSCs) have risen in only nine years as the hottest next-generation photovoltaic technology and are predicted to be one of the most serious challengers for the silicon-based solar cell market. PSCs have been found to efficiently convert up to 28% of captured solar energy into electricity. It took almost 42 years for all other flexible solar cell technologies to reach an efficiency level of 22.6%.
Perovskite describes a class of mineral composed of calcium, titanium, and oxygen discovered in the Ural Mountains by Lev Perovski. The name is broadly used when referring to any material that shares the same crystal structure as the originally described perovskite. PSCs are designed to utilize organometallic halide perovskite absorber layers (i.e., a hybrid organic-inorganic lead or tin halide material), which contribute significantly to its high performance.
Although PSCs have been mainly the result of extensive academic research (3,200 published papers and 110,000 citations during 2017 alone), its expansion and development continues to address how to decrease costs of production, enhance its poor lifespan, reduce levels of toxicity or test additional nontoxic materials, and translate its high power-conversion efficiency found under lab settings to commercial products.
Why are perovskites ideal for the production of flexible solar panels?
- The organic-inorganic hybrid perovskites achieve crystallization at very low temperatures, which makes the fabrication of flexible cells possible.
- Perovskite material has advantageous mechanical properties such as the ability to endure compression, tortuosity, and a certain degree of bendability. These properties contribute to PSCs’ “defect tolerance” and flexibility. Compared to silicon solar cells that need to be perfectly aligned and where any damage renders the entire device unusable, PSCs, once layered on any surface, start absorbing and generating electric charges.
- Perovskite materials are able to dissolve in organic polar solvents, allowing high-quality thin films to be deposited on any surface using simple solutions (spin-coating, spray coating, inkjet printing, slot-die coating, and blade coating). These deposition techniques can be easily integrated into the roll-to-roll production of flexible PSCs.
- Perovskite material band gaps have high light absorption coefficients that allow the fabrication of ultra-thin PSCs without compromising their conversion efficiency.
- PSCs have a high power-per-weight ratio, currently at 23 watts per gram, the highest of any existent solar cells on the market today. This property could facilitate PSCs’ application in aerial vehicles that require a prolonged flight range (i.e., airplanes, quadcopters, weather balloons) needed for environmental and industrial monitoring, rescue and emergency response, and tactical security applications.
In a nutshell, taking advantage of perovskite’s physical properties, flexible PSCs can absorb solar energy with active layers that are 100 times thinner than those layers produced for silicon solar cells, efficiently produce electricity, and keep production costs low, opening up a vast range of yet-to-be imagined applications.
Current markets and the fate of flexible perovskite solar cells:
Three types of flexible thin-film solar technologies — amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS) — currently dominate the market. Recent statistics indicate that in 2017, CdTe and CIGS attained 51% and 42% of total global flexible photovoltaic cell production, respectively. The production of a-Si thin films dropped drastically to 7%, due perhaps to its low efficiency and higher costs to achieve the desired efficiency.
Flexible PSCs are taking gigantic steps forward. The Australian company Greatcell Solar has taken the direction of providing PSC raw materials, specific chemicals, components, and equipment aiming to assist partners in the manufacture of PSCs. Swift Solar, an American company, will start the design and manufacture of PSCs with an initial investment of $4.6 million in early 2019.
One of the most active companies, Saule Technologies, which produced the first inkjet printing manufacturing process for perovskite sheets, has started the production of the first large, flexible, 1-m2-format modules. The initial efficiency is expected to be around 10%, with an initial price of $58 per square meter. Skanska, a Japanese company partnered with Saule, has installed a commercial prototype on the Spark office building facade in Warsaw. Their flexible PSC prototype is 1.3 x 0.9 m2 and contains 52 photovoltaic modules fabricated using inkjet printing technology. Huis Ten Bosch Co. has also installed 72 photovoltaic Saule flexible PSC units to power a billboard for the South Arm of its Henn na hotel in Tokyo.
Finally, in January 2019, Oxford PV announced a new certified efficiency world record of 28% for a 1-cm2 perovskite-silicon tandem solar cell. Oxford PV has over $59 million of funding aimed to transfer its perovskite technology into silicon solar cells. Oxford PV prototypes passed the tests under high humidity and temperature that are required for certification of solar panel products.
All these companies paint a positive future for the massive production of fully functional, stable, durable, and highly efficient flexible-thin PSCs by the end of 2021. However, PSCs still need to prove that those high efficiency rates achieved under laboratory standards can also be maintained after installation and can endure diverse weather factors. This far, PSCs have reached and improved efficiencies in ways that silicon will be unable to match.
