ADVANCED PHOTOVOLTAICS
Perovskite Tandems (PP3.1)
PP3.1: Perovskite Tandems
The aim of this work package is to develop perovskite tandem cells with either silicon or alternate material bottom cells that will achieve >30% efficiency, and to develop manufacturable approaches to deliver these high efficiency tandem cell technologies.
Investigators: Anita Ho-Baillie, Udo Bach, Kylie Catchpole, Nathan Chang, Klaus Weber, Thomas White, Gregory Wilson
PP3.1.1 Stable High Efficiency Wide and Narrow Bandgap Perovskite Cells
In this activity, high performance wide and narrow bandgap perovskite cells will be demonstrated. While the ideal bandgap combinations for double junction tandem are 0.98eV; 1.87eV and for triple junctions 0.82eV; 1.44eV; and 2.26eV, a range of bandgaps for each junction is acceptable.
Significant voltage deficit in current high bandgap perovskite cells is a bottleneck to high efficiency tandems. Therefore, a key focus will be the demonstration of high voltage high bandgap cells with minimum halide segregation building on the knowledge on halide segregation and remixing.
One major origin of the efficiency loss for wide-bandgap perovskite solar cells is the large open-circuit voltage loss in contact design and some perovskite films. A series of strategies including perovskite compositional engineering, additive engineering, interfacial engineering and device engineering, have been proven effective at minimizing non-radiative recombination and reducing voltage losses.
This activity will extend the previous work by developing and investigating novel defect passivation strategies guided by sophisticated modelling and characterization techniques, including the accurate quantification of the relative contributions from bulk and surface defects.
It will also develop effective encapsulation methods for stable perovskite and tandem solar cells and conduct extended stability assessments using both accelerated testing and field tests. The feedback gathered from these assessments will be used for material, process, and device development with the aim of improving tandem stability.
All material and cell design decisions to pursue high efficiency will be guided by the stability research planned in PP2. Through these, a significant efficiency gain of perovskite solar cells will be realized, contributing to boosting the silicon/perovskite tandem efficiency well beyond the limits of standard silicon solar cells.
PP3.1.2 Demonstrations of Stable Ultra-High Efficiency Perovskite Tandems
In this activity, perovskite-based tandems with various bottom cells using monolithic integration and/or mechanical stacking will be demonstrated. The aim will be to achieve ultra-high efficiency with each technology investigated.
For mechanically stacked perovskite tandems, integration strategies to reduce optical losses and maximise optical coupling for different types of tandems will be developed.
For monolithically integrated tandems, cell designs will be developed taking into account the processing compatibility of each stage, including temperature requirements and texturing or surface roughness of bottom cells, all of which impact fabrication processes.
As part of this work package, device modelling will be carried out to identify key optical and electrical losses of current tandems and to develop new cell designs for future tandems.
As demonstrations of double junction monolithically integrated perovskite-perovskite tandem become more mature, triple junction tandems will be demonstrated as part of ACAP.
PP3.1.3 Advanced Perovskite/Silicon Tandem Design Using Low-Cost Approaches
For Si/perovskite tandems to succeed, they need to be produced at a low cost.
UNSW and ANU cost studies indicate that the demonstrated high-efficiency silicon/perovskite tandems involve prohibitively expensive material and processes as well as too many processing steps, making the tandem cost overhead largely outweigh the efficiency gain.
This activity will address this challenge, which is a crucially important step towards the commercialization of silicon/perovskite tandem technology.
Besides requiring excellent performance for each of the sub cells, the silicon/perovskite tandem device also demands a good mechanical, optical, and electrical interconnection to efficiently connect the two sub cells.
This activity will develop new concepts and advanced designs to simplify the tandem structure and fabrication processes, building on high efficiency interconnect-free concepts that have been developed at ACAP.
According to UNSW and ANU cost studies, to produce low-cost silicon/perovskite tandem, it is also important to mitigate cost barriers associated with high-cost processes and materials.
Therefore, this activity will further simplify the tandem device structure including the top transparent contact stack, develop abundant materials for use as contact and electrode and optimize the fabrication process to enable high-efficiency and stable tandems to be manufactured at low cost.
Efforts will continue to be devoted to tandems built on the PERC/TOPCon silicon solar cells, the two market-dominating technologies in the coming ten years, in combination with the state-of-the-art perovskite materials developed in 3.1.1 and 3.1.2, thereby providing a direct route to achieve ultra-high efficiency tandems with low cost.
PP3.1.4 Techno-Economic Analyses
In this activity, techno-economic analyses will be performed to direct research to commercially relevant outcomes, comparing monolithic tandems and mechanical-stacked tandems. The comparison will be insightful to evaluate the integration-effort-savings in mechanical-stacked tandems and the greater flexibility in cells fabrication and optimization. These developments will incur extra cost from the additional wiring and insulating layers required interfacing with the stacks that will need to be assessed for impact on performance, manufacturability and durability.
Cost drivers for each of the perovskite-based tandem technologies will be assessed and identified to inform research.
