- Solar cells
Alex Zettl and Onur Ergen of Lawrence Berkeley National Laboratory have developed graded bandgap perovskite photovoltaic cells with good output current and power conversion efficiency by implementing a new cell architecture. GaN was chosen to replace the typical TiO2 electron transport layer to provide a better surface morphology and enhanced electron injection due to its ability to be heavily doped. A graphene aerogel makes an excellent barrier layer to moisture ingress and improves hole collection efficiency in the hole transport layer. The aerogel also promotes a more crystalline perovskite structure. Choosing the right metal cation and varying halide anion concentration also successfully establishes bandgap tuning of the perovskite absorber layer. The combination of GA and h-BN enables this bandgap formation, and this configuration produces cells that are reproducible and stable.
Organic-inorganic perovskite solar cells are typically prepared in a single bandgap configuration, where an absorber layer (ABX3, A=CH3NH3(MA); B=Pb, Sn; and X=Cl, Br, I) is sandwiched between an electron transport layer (ETL) and a hole transport layer (HTL). Following significant effort in optimizing interface layers to control the carrier dynamics, power conversion efficiencies (PCEs) for this design, for a single cell, have surpassed 20%. In addition, due to the toxicity of lead in the absorber layer, lead-free tin halide perovskite solar cells have gained tremendous importance. However, lead-free cells do not exhibit such high photovoltaic performances (e.g., less than 7%) due to chemical instability.
The tunable bandgap of methylammonium-lead-halide has also led researchers to construct multijunction tandem cells which aim to maximize the solar irradiative spectrum. In these tandem cells, the perovskite layer can be integrated with crystalline silicon (c-Si) and copper indium gallium selenide (CIGS). However, the tandem cell requires complex electrical coupling and interconnection between the perovskite sub-cells, which generates electron-hole recombination centers
STATUS: Issued U. S. Patent 10,403,708. Available for licensing or collaborative research.