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

Abstract

Multi-junction architectures are utilized in photovoltaic (PV) technology to widen spectral range, increase voltage and/or current, and hence deliver higher overall power conversion efficiencies (PCEs). However, accurate approaches for simulating multi-junction PVs using the electro-optical properties of real materials are somewhat scarce—particularly in the context of novel applications such as indoor PVs, where the illumination spectrum differs from natural sunlight. Herein, we present a robust methodology—alongside an open-source simulation tool—for modeling multi-junction PVs while accounting for intrinsic PV features, including sub-gap absorption, band-filling effects, and radiative couplings between junctions. Although we primarily focus our investigation on perovskite-based multi-junction devices, our approach is extendable to any class of PV material. We apply it in the context of indoor PVs by assuming the LED-B4 spectrum as a representative light source. At a typical illuminance of 1000 lux, we find that PCEs above 60% are possible by combining a 2.1 eV wide-gap top cell with a 1.0–2.0 eV narrow-gap bottom cell, meaning that a suitable wide-gap semiconductor could be coupled with almost any conventional solar cell to achieve high performance. Using the spectral responses of real PV devices, we then predict optimal material configurations under LED-B4 illumination, before probing the spectral versatility of these devices under a variety of indoor light sources and intensities. We find that the maximum power point voltage is mostly independent of light source, while PCE is more sensitive due to changes in current density, which provides insight into how laboratory-optimized devices may perform in realistic scenarios