In this paper, we have utilized finite difference time domain (FDTD) method to investigate the solar energy absorption of hybrid solar cells (HSCs) with trapezoid-pyramidal structure (TPs) based PEDOT:PSS/c-Ge. We have changed some parameters of TPs (different heights and different ratios of top to bottom) to study its effects on the solar energy absorption for HSCs. The optimization of geometric parameters is based on the maximum solar energy absorption efficiency. The optical absorption of the HSCs with TPs is basically above 90% from ~300 nm to ~1300 nm and the average solar energy absorption is 93.8% under AM 1.5 solar spectrum (from 300 nm to 1500 nm). Simultaneously, we have calculated the short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), maximum power (Pmax) and photoelectric conversion efficiency (PCE) respectively through DEVICE software. The results of electrical simulation reveal that the maximum Jsc is 43.47 mA/cm2 , it is 45.73% higher than planar PEDOT:PSS/c-Ge HSCs. Moreover, to further explain the mechanism of solar energy absorption of HSCs with TPs, the logarithmic figures of electric field intensity for trapezoid-pyramidal PEDOT:PSS/c-Ge HSCs and planar PEDOT:PSS/c-Ge HSCs at different wavelengths are analyzed. The result shows that TPs array has shown excellent light-trapping effect. This work reveals the huge potential of c-Ge HSCs in solar absorption, and at the same time has certain guiding significance for the structural design of Ge SCs. It is believed that through further exploration, the conversion efficiency of c-Ge HSCs will be further improved.

Introduction

In recent years, with the development of society, energy and environmental issues have attracted much more attention. People pay more and more attention to research clean and renewable energy, such as wind energy, geothermal energy, tidal energy, etc. (Orrego et al., 2017; Sun et al., 2018; Zhang et al., 2020). However, due to the infinite energy provided by the sun, the photovoltaic devices which can directly convert solar energy into electricity have caused extensive research (Yi et al., 2019; Wu et al., 2020; Gao et al., 2019). As we know, researchers have been working to improve the efficiency of solar cells (SCs) (Li et al., 2019; Iman et al., 2020; Van der Heide et al., 2009). The photoactive layer realizes the conversion from light energy to electricity by absorbing photons to excite electrons from the valence band to the conduction band, and then separates the generated electron-hole pairs through a PN junction to form photocurrent. The more light energy is absorbed, the more electron-hole pairs are generated, the larger the photocurrent is generated, and the efficiency of the SCs will be improved accordingly (Li et al., 2019). In order to improve the light absorption efficiency, various microstructures are fabricated on the active layer to improve the solar energy absorption (Liu et al., 2017).