Lead-free Materials for Solar-Cell Production

NU 2016-131, NU 2015-139, NU 2015-050, NU 2014-135, NU 2014-052, NU 2014-049

PRIMARY NVENTOR
Mercouri Kanatzidis

SHORT DESCRIPTION 
New, environmentally safe, inorganic materials for the production of stable and cost-effective solar cells 

BACKGROUND
Solar cells are photovoltaic semiconductor devices that convert sunlight directly into electricity when photons from the sun excite electronics in a material, generating electric current. Sales of solar cells totaled $170.6 billion in 2022. Future potential is vast considering that currently only 3.3% of the electricity in the United States is generated from photovoltaic modules. One type of solar cell technologies with enormous potential is a new generation of perovskite-based solar cells. Perovskite solar cells achieve high efficiency while having tunable properties and low cost of fabrication. However, these perovskites exhibit long-term instabilities and toxicities associated with lead compounds that limit widespread applications. Thus, to realize commercial applications of this technology, it is important to achieve analogous optical and photovoltaic performance using lead-free and air-stable organic−inorganic compounds for ambient processing that offer growth orientation control of films and reproducibility.

ABSTRACT
Northwestern scientists have developed lead-free perovskite-like materials for use in photovoltaic materials for solar cell production. While perovskites have found ample use in solar cell design due to their high efficiency and solution processability, these minerals often utilize toxic lead (Pb) and are unstable under ambient conditions making them a suboptimal choice for large-scale solar cell production. To solve these issues, Prof. Kanatzidis and colleagues have produced tin (Sn) and Germanium (Ge) perovskite-like materials that do not contain harmful metals, while still displaying remarkable similarities to Pb perovskites. Kanatizidis’ innovations in perovskite production also included a fast, low-temperature, gas-solid crystallization method for the reproducible fabrication of high-quality perovskite films without pinholes, which allows better control over the dynamics of nucleation and crystal grain growth of AMX3 perovskite film. Additionally, new Sn halide perovskites utilize 2D multi-layer perovskites in place of problematic 3D analogs that have poor reproducibility. This reliable fabrication improves long-term chemical and operational stability and allows for functionalization with charge-transport active compounds separating the perovskite sheets which can lead to integrated solar cell compounds. Their innovative materials are inexpensive to produce, do not pollute the environment, and are stable at ambient conditions, which greatly simplify solar cell manufacturing. In laboratory tests, photovoltaic cells utilizing these alternative “safe” materials have adequate conversion efficiency, which is currently as high as 8%. By combining low-cost starting materials with simple and scalable manufacturing procedures, this new technology may facilitate the implementation of photovoltaics into the current electricity production landscape.

APPLICATIONS 

• Solar panels

• Portable electronics

• Solar power plants

ADVANTAGES 

• Stable in ambient conditions

• Less toxic and harmful to environments

• Scalable production

• Inexpensive

PUBLICATIONS

Song TB, Yokoyama T, Stoumpos CC, Logsdon J, Cao DH, Wasielewski MR, Aramaki S, Kanatzidis MG. (2017) Importance of reducing vapor atmosphere in the fabrication of tin-based perovskite solar cells. Journal of the American Chemical Society. 139(2):836-42.

Yokoyama T, Song TB, Cao DH, Stoumpos CC, Aramaki S, Kanatzidis MG. (2017) The origin of lower hole carrier concentration in methylammonium tin halide films grown by a vapor-assisted solution process. ACS Energy Letters, 2(1):22-8.

Qiu X, Cao B, Yuan S, Chen X, Qiu Z, Jiang Y, Ye Q, Wang H, Zeng H, Liu J, Kanatzidis MG. (2017) From unstable CsSnI3 to air-stable Cs2SnI6: A lead-free perovskite solar cell light absorber with bandgap of 1.48 eV and high absorption coefficient. Solar Energy Materials and Solar Cells,1;159:227-34.

Ke W, Stoumpos CC, Zhu M, Mao L, Spanopoulos I, Liu J, Kontsevoi OY, Chen M, Sarma D, Zhang Y, Wasielewski MR. (2017) Enhanced photovoltaic performance and stability with a new type of hollow 3D perovskite {en} FASnI3. Science advances, 3(8):e1701293.

Cao DH, Stoumpos CC, Farha OK, Hupp JT, Kanatzidis MG (2015). 2D homologous perovskites as light-absorbing materials for solar cell applications. Journal of the American Chemical Society, 137(24), pp.7843-7850. 2015 

F. Hao, C. C. Stoumpos, D. H. Cao, R. P. H. Chang, Kanatzidis MG (2014) Lead-free solid-state organic–inorganic halide perovskite solar cells. Nature Photonics 8, 489-494.

F. Hao, C. C. Stoumpos, D. H. Cao, R. P. H. Chang, Kanatzidis MG (2014) Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells.  Journal of the American Chemical Society 136, 8094-8099.

IP STATUS
A portfolio of US and PCT applications have been filed.