Hybrid Organic Inorganic Perovskites for Water Splitting
LaboratoryNational Renewable Energy Laboratory (NREL)
Capability ExpertKai Zhu, Joseph Berry
Process and Manufacturing Scale-Up
Node Readiness Category2: Photoelectrochemical (PEC)
The hybrid organic inorganic perovskite (HOIP) team at NREL has the ability to grow high-quality hybrid perovskites for various solar conversion and optoelectronic applications. The typical hybrid perovskite materials have an ABX3 structure, where A is monovalent cation such as methylammonium (MA+), formamidinium (FA+), or cesium (Cs+); B is a bivalent cation such as Pb2+ or Sn2+; and X is a halide anion such as I-, Br-, or Cl-. The NREL HOIP team is capable of producing >20% perovskite solar cells with either a normal n-i-p (e.g., glass/TCO/ETL/perovskite/HTL/Ag; ETL/HTL: electron/hole transport layer) or an inverted p-i-n (e.g., glass/TCO/HTL/perovskite/C60/BCP/Ag) device structures for different applications. The bandgap of perovskites can be varied from about 1.2 eV to 2.3 eV by changing A-, B-, and/or X-site compositions. These perovskites can be synthesized in various forms including polycrystalline thin films, single crystals, and nanocrystals. In addition to the standard 3-dimensional (3-D) perovskite ABX3 structure, the NREL HOIP team also has expertise on fabricating 2-D or quasi 2-D perovskites with a general structure of (R-NH3)2An-1BnX3n+1, where n=1 corresponds to a 2-D perovskite sheet whereas n=∞ corresponds to the 3-D perovskite structure. It is worth noting that the NREL HOIP team can produce >20%-efficient solar cells with a wide range of perovskite bandgaps including ~1.7 eV perovskite composition which is suitable to pair with Si or similar bandgap materials for tandem devices. The wide selection of material compositions and continuous bandgap tuning coupled with high conversion efficiencies are very attractive for PEC applications especially tandem or multijunction PEC electrodes or hybrid photo-electrodes for H2 production.
As part of HOIP solar cells fabrication, the team also has physical vapor deposition (PVD) capabilities for the 3D perovskite active layer materials across the typical photovoltaic material composition space, as well as oxide or metal contact layer materials. The PVD tools include traditional magnetron based sputtering which can be used to produce single or mixed composition materials and multilayers for 3-4 1”x1” samples or fixed compositions at larger areas up to 5”x5” for typical transparent oxides (e.g, IZO, GZO). More flexible PVD capabilities that can also be leveraged for custom electrode depositions also includes pulsed laser deposition which can handle up to 2” x 2” and permits graded oxide composition electrodes, complex multilayers contacts to be deposited. Critical to many of these is production of thin protective layers which permit integration of PVD based materials without compromising the HOIP materials via atomic layer deposition (ALD) or related chemical vapor deposition. ALD can also be used as a means of creating encapsulation for improved perovskite stability alone or in combination with other PVD layers. Metal deposition, as well as select dielectric oxides, can be done via thermal or e-beam deposition capabilities; again these can be used as electrodes and/or encapsulation layers. These various materials also enable both integration of multiple absorbers for multijunctions and serve as electrodes for integration of catalysts for hydrogen evolution.
Standard lateral sample size is 1”x1”, but samples of dimensions up to about 5”x5” are also possible. The effective perovskite film thickness ranges from about 100 nm to 1–2 µm.
The hybrid perovskite R&D capabilities include several strongly interconnected areas on perovskite synthesis, device fabrication, fundamental characterizations. Perovskite synthesis can be done under controlled atmosphere with specific perovskite composition, grain morphology, film thickness. Perovskite based devices can be fabricated with various device architectures using various contact/transport/protection layers from mm2 at the lab scale to inch2 that is relevant to industrial partners. Various characterizations at different length and time scales provide a wide range of information on perovskite structure, charge carrier dynamics, and device operation characteristics. The integration of these state-of-the-art capabilities coupled with extensive experience from expert researchers is unique within the national lab system with demonstrated track record in various aspects of perovskite-based solar cell development [1–6].
During the past several years, NREL’s HOIP team has published >100 high-impact scientific publications and also has generated a large portfolio of intellectual properties on perovskites . NREL’s HOIP team can produce >20%-efficient PV devices especially for ~1.7-eV perovskite that is suitable to build tandem cells with Si or similar low-bandgap materials. The demonstrated high efficiency & quality of our perovskite materials is also unique in the national lab system. Several companies and many university teams have been working with the NREL HOIP team to conduct R&D on perovskites for PV. HOIP materials are versatile semiconductors suitable for a range of optolelectronic applications such as emitters, photodetectors and X-ray sensors. HOIPs also have potential in next generation optoelectronics applications such as neuromophic computing and/or quantum information processing by being an enabling material for memsitors, or spintronics devices like spin diodes.
We can produce samples on substrates from about 1”x1” to 5”x5” size depending on the specific project needs. We have great flexibility of tuning perovskite composition, perovskite structure, device architecture, transport/contact layers to enable easy testing/developing of individual layers with industrial partners or university collaborators. The various capability tools closely located at NREL has been an integral part in the technological work done under CRADAs/TSA with private sector institutions as well as universities via different research agreements. NREL’s primary HOIP capabilities are currently supported by the SETO program for the PV application. The HOIP team has availability to support HydroGEN projects in addition to the current work. The HOIP capabilities described above (including synthesis, characterization, multilayer deposition) are available to HydroGEN. Standard samples can be provided to EMN partners. We can also work with collaborators to have unique designs to meet the specific project needs/goals.
This described capability can allow researchers to work with NREL experts to test or develop specific perovskite composition and structure, and optimize certain device layers for improved efficiency, durability, and scalability for HOIP development or integration with other materials for tandem/multijunction structures for PEC electrodes for water splitting. This would significantly reduce the development cycle. It can also be used to generate standard samples with good reproducibility and reliability in order to help EMN collaborators/partners to develop the specific electrode structures at their own research locations. All these activities will be in direct support of the HydroGEN goals.
Figure 1. Photograph of the HOIP capabilities at NREL: (1) Perovskite synthesis covering from solution processing to vapor phase deposition, from polycrystalline thin films to perovskite single crystals, and from 3-D perovskites to lower dimensional perovskites (2-D structures or 0-D quantum dots); (2) Device functional/contact layer control via sputtering, ALD, thermal/e-beam evaporation, and other physical vapor phase deposition; and (3) State-of-the-art characterizations on structural, chemical, and optoelectronic/photophysical properties. All these capabilities are closely located at NREL to ensure effective R&D support.
- Christians, J.A. et al. Tailored interfaces of unencapsulated perovskite solar cells for >1,000 hour operational stability. Nature Energy 3, 68-74 (2018).
- Li, Z. et al. Scalable fabrication of perovskite solar cells. Nature Reviews Materials 3, 18017 (2018).
- Swarnkar, A. et al. Quantum dot–induced phase stabilization of α-CsPbI3 perovskite for high-efficiency photovoltaics. Science 354, 92-95 (2016).
- Yang, M. et al. Perovskite ink with wide processing window for scalable high-efficiency solar cells. Nature Energy 2, 17038 (2017).
- Yang, Y. et al. Observation of a hot-phonon bottleneck in lead-iodide perovskites. Nature Photonics 10, 53 (2015).
- Zhao, D. et al. Low-bandgap mixed tin–lead iodide perovskite absorbers with long carrier lifetimes for all-perovskite tandem solar cells. Nature Energy 2, 17018 (2017).