1. Perovskite/silicon two-terminal tandem photovoltaic modules

The use of perovskite solar cells in tandem photovoltaic (PV) modules based on silicon PV is an attractive application for perovskites, as perovskite-on-silicon tandem solar cells offer a route in exceeding the power conversion efficiency (PCE) of the market-dominant silicon single-junction photovoltaics. In order to improve the PCE of silicon single-junction solar cells, a key strategy in light management is the texturing of the crystalline silicon surface for enhancing light incoupling as well as light trapping[1][2]. Since the micron-scale texture facilitates light incoupling for the complete optical spectrum, the adoption of textures is also of high relevance in perovskite/silicon tandem PV modules[3].

Under realistic conditions, the spectrum and intensity of irradiance is changing continuously with time, and is not comparable to the illumination under conventional standard test conditions (STC) for deriving the solar cell’s PCE. The calculation of energy yield (EY) under realistic irradiation conditions offers the possibility to carefully optimize the structure of perovskite/silicon tandem PV modules. For this, our recently developed EY platform accounts for the variations in the share of specular and diffuse irradiance with time as well as angular dependency of incident light. The model uses the transfer-matrix method combined with statistical ray tracing for the optical modelling of the device and the one-diode model for the electrics. With input of irradiance data of a typical meteorological year (TMY3) from NREL[4] for many locations with various climate zones, we calculate the EY of the solar cell, and predict the optimal structure for different device architectures as well as for different locations. Since the bandgap of perovskites is tunable[5], we further evaluate the EY for different bandgaps finding the optimal bandgap for all investigated architectures and locations.

2. Energy yield modelling of different architectures with planar and textured interfaces

In this work, we focus on the two-terminal (2T) configuration of perovskite/silicon tandem PV modules with monolithic interconnection of perovskite top cell and silicon bottom cell. There is also work on the EY modelling of perovskite/CIGS tandem PV modules, with the comparison of 2T and four-terminal (4T) configuration[6]. For perovskite/silicon 2T tandem PV modules the EY is calculated for three different architectures, a planar with flat front and rear side, a double-side texture with texture at the front and rear side, and rear texture only[7]. The EY of all perovskite/silicon 2T tandem PV modules with a perovskite bandgap of 1.72 eV is compared to the EY of a reference silicon single-junction PV module with a double-side textured architecture, and the relative enhancement in EY is evaluated. These calculations are performed for three locations with various climate conditions with an optimized module tilt angle and an optimal perovskite absorber layer thickness.

We optimize the perovskite absorber layer thickness in order to minimize losses due to mismatch of generated currents in both subcells. Since current matching depends mainly on the spectrum and intensity of irradiance, the maximal EY is found for different perovskite absorber layer thicknesses than under STC. This fact has to be considered in optimizing the layer stack of perovskite/silicon 2T tandem PV modules. The EY increases for all three architectures and the highest relative enhancement in EY with 26–28% is shown for the perovskite/silicon 2T tandem PV module with double-side texture, whereas it is 12–14% for the planar and 19–22% for the rear texture. In order to find the optimal perovskite bandgap for a 2T tandem, we further evaluate various perovskite bandgaps in the range of 1.55–1.88 eV. With this work we demonstrate the importance of wide bandgap perovskites to the application in perovskite/silicon 2T tandem PV modules.