Research Paper: Thermodynamic principles for optimizing multi-junction photovoltaics — Exemplified for perovskite-based indoor photovoltaics

Scientific Summary

This study introduces a novel, robust methodology and accompanying open-source simulation tool for optimising multi-junction photovoltaics (PVs), particularly for indoor applications. The main goal was to accurately model complex PV features, including sub-gap absorption, band-filling effects, and realistic bidirectional radiative couplings between junctions. Key findings indicate that power conversion efficiencies (PCEs) above 60% (reaching 77% with radiative coupling) are thermodynamically possible for indoor PVs under conditions like LED-B4 spectrum at 1000 lux. This high performance can be achieved by combining a 2.1 eV wide-gap top cell with a 1.0–2.0 eV narrow-gap bottom cell, suggesting that a wide range of conventional solar cell materials are suitable for the bottom junction. The research also demonstrates that the maximum power point voltage (Vmpp) remains largely independent of the light source, while PCE is more sensitive to changes in current density.

Why it Matters

These findings are vital for accelerating the design and deployment of high-efficiency, versatile multi-junction PVs for applications like indoor energy harvesting and the Internet of Things (IoT). The insights gained into device performance under diverse real-world indoor settings, particularly the independence of Vmpp from the light source and the PCE's sensitivity to current density, are crucial for advancing next-generation indoor PV technology.

Publication Details

Kay, A.M., Riley, D.B., Burwell, G., & Meredith, P. (2025), Thermodynamic principles for optimizing multi-junction photovoltaics—Exemplified for perovskite-based indoor photovoltaics. APL Energy, 3, 036102. https://doi.org/10.1063/5.0266374

Fluxim Tools Used

The paper mentions Setfos (Fluxim AG) as one of several "multi-scale electro-optical device models" available for optimizing multi-junction PV designs. However, this study developed and utilized its own robust, open-source simulation methodology and computational tool for its core investigations.