Spatially-Resolving the Optoelectronic Properties in Textured, Multi-junction Perovskite/Si Solar Cells
Elizabeth Tennyson a, Kyle Frohna a, William Drake a, Quentin Jeangros b, Chien-Jen Yang b, Fan Fu b, Jérémie Werner b c, Christophe Ballif b, Samuel Stranks a
a Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
b École Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin-Film Electronics Laboratory (PV-Lab), Rue de la Maladière 71b, Neuchâtel 2002, Switzerland
c Chemical and Biosciences Department, University of Colorado, Boulder, University of Colorado, Chemical and Biosciences Department, Boulder, Colorado 80309, United States
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Elizabeth Tennyson, 173
Publication date: 11th February 2019

To accelerate solar energy adoption and mitigate the consequences of climate change, researchers are focusing their efforts towards multi-junction photovoltaics (PV) to boost the total amount of solar energy harvested, ultimately decreasing the cost/watt. One approach is to integrate another light-absorbing material on top of an already commercialised, high-performance Si solar cell. Metal-halide perovskites are excellent candidates for the top cell, as they have high power-conversion efficiency (η), are low cost, and have tunable optoelectronic properties [1]. The perovskite bandgap can be adjusted to the theoretical optimal one, of 1.75 eV for a two-terminal device, by altering the constituent elements within the material’s composition [2]. To date, the maximum perovskite/Si tandem solar cell has reached a remarkable η=28%, yet to reach the desired η=30%, further light-management optimisation is necessary.

State-of-the-art multi-junction PV devices are currently textured with micron-sized pyramids that are designed in size and shape for enhanced photon in-coupling [3]. However, the texturing processes are optimised solely for the underlying Si device and not necessarily for the entirety of the perovskite/Si stack. Therefore, it is reasonable to assume that with a new texturing scheme, photon recycling and lateral light absorption will be enhanced by altering the x, y, or Θ, as illustrated in the top half of the TOC image, increasing η. In addition, the morphology of this solar cell type consists of two multi-scale spatially varying components: (i) the ≈5 µm sized Si pyramids and (ii) the <1 µm diameter polycrystalline grains of the perovskite. Each construct will introduce discrete, unique, and localised non-uniformities of the optoelectronic properties [4], [5]. In order to understand how the micron-sized pyramids and grain-to-grain heterogeneity influence device performance, we spatially and spectrally resolve the local optoelectronic properties for perovskite/Si multi-junction samples with variable charge transport layers and texturing schemes. For this, we implement wide-field hyperspectral photoluminescence and optical (reflection/transmission) microscopy to acquire maps of both the emission and absorption, with ~500 nm spatial resolution, see bottom half of TOC image. We perform these measurements on a wide range of perovskite/Si solar cells, and by visualising these optoelectronic properties, we reveal heterogeneous emission/absorption distributions with transport layer dependent bandgap segregation. Looking ahead, we provide new insights and suggestions for improved light capturing to enhance performance.

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