Perovskite photovoltaics are a new class of light absorbers with exceptional and unparalleled progress in solar power performance. A perovskite is any material with a specific ABX3 crystal structure. In photovoltaic applications, the A cation can be either organic, inorganic, or hybrid in composition. The B component is typically a metal cation such as lead, and X is a halide such as iodine or bromine. Work on solar cells using perovskite materials has advanced rapidly as a result of the material’s excellent light absorption, charge-carrier mobilities, and lifetimes – resulting in high device efficiencies with low-cost, industry-scalable technology. While the potential for perovskite photovoltaic devices is high, commercialization will require overcoming other challenges relating to material stability, efficiency, and environmental compatibility.
Over the last decade, scientists and engineers have revolutionized perovskites by incorporating formamidinium (HC(NH2)2+, FA+) cation into organic-inorganic lead halide devices. Perovskites containing FA+ show improved structural/chemical/opto-electronic properties, wider absorption spectral window into the NIR range, and longer charge carrier diffusion length. While these devices show great promise, some have already demonstrated efficiencies above 20%, they have so far shown excellent performance only when adopting a mesoscopic architecture. To successfully adopt FA-based perovskite layers in planer device geometries for various applications, alternative procedures for forming thick, uniform, material with enhanced charge transport will be necessary.
Researchers at NREL have created a FA-based perovskite device using an oriented crystal growth approach. Although this has traditionally been accomplished by incorporating chlorine, this approach has not been applied as successfully in FA-based perovskite devices due differences in reaction rates during sublimation. Researchers instead fabricated a uniaxially-oriented high-crystalline perovskite layer by utilizing a facile and simple topotactic oriented attachment (TOA) process. The resulting device exhibits unprecedented high 9 GHz charge-carrier mobility (up to 70.8 cm2V-1s-1) and an efficiency of 19.7%, comparable to that of mesoscopic perovskite structures.
This technology is within the Perovskite Film Chemistry group of NREL’s perovskite portfolio. For further information regarding NREL's broader perovskite portfolio, please visit NREL's Perovskite Patent Portfolio website.
To learn more about Oriented Perovskite Crystals and Methods of Making the Same, please contact Bill Hadley at Bill.Hadley@nrel.gov.
Applications and Industries
- Enables high performance FA-based perovskite planar heterojunction devices
- Improved charge carrier mobility
- Versatile process for other alloys including state-of-the-art triple cation and mixed halide perovskite compositions