The cell-to-panel efficiency gap observed in a-Si/c-Si heterojunction solar cells is one of the key challenges of this technology. To systematically address this issue, we describe an end-to-end ...modeling framework to explore the implications of process and device variation at the module level. First, a process model is developed to connect the a-Si deposition parameters to the device parameters. Next, a physics based device model is presented which captures the essential features of photo-current and diode injection current using the thermionic-diffusion theory. Using the process and device models, the effects of process conditions on cell performance are explored. Finally, the performance of the panel as a function of device and process parameters is explored to establish panel limits. The insights developed through this process-to-panel modeling framework will improve the understanding of the cell-to-panel efficiency gap of this commercially promising cell technology.
Coupling perovskite and silicon solar cells in a tandem configuration is considered an attractive method to increase conversion efficiency beyond the single-junction Shockley-Queisser limit. While a ...mechanically-stacked perovskite/silicon tandem solar cell has been demonstrated, a method to electrically couple perovskite and silicon solar cell in a monolithic configuration has not been demonstrated. In this contribution, we design and demonstrate a working monolithic perovskite/silicon tandem solar cell, enabled by a silicon tunnel junction, with a VOC of 1.58 V. We further discuss possible efficiency loss mechanisms and mitigation strategies.
Light management in the Si bottom cell of a GaAs/Si tandem system is crucial due to the bandgap mismatch of the two materials, which results in a low current of the bottom cell. To evaluate the light ...coupling and light trapping, we developed an optical model to simulate the light absorption in the silicon bottom cell. This optical model is an extension of Basore's analytical model. By comparing the simulation with the measurement of the prototype tandem solar cell, we find that the Si bottom cell can gain up to 2.4 mA/cm2 photocurrent by improving light coupling. In addition, we study the impact of the rear surface reflectance on the photocurrent in the Si bottom cell. We observed that ~17% relative increase in current generated in this bottom cell can be achieve by changing the rear surface design from a full area metal contact to a local-back-surface-field configuration.
With the advent of high-bandgap perovskites, the opportunity now exists to make tandems with perovskites on top of silicon. We have prototyped a mechanically stacked tandem, achieving 17.9% certified ...efficiency using a perovskite cell with a silver nanowire mesh electrode. We have also prototyped a monolithically integrated tandem on silicon, with the two subcells electronically connected by band-to-band tunneling in the silicon. The primary challenges to propelling perovskite/silicon tandems into a high-efficiency (>25%) regime are spiro-OMeTAD parasitic absorption, perovskite crystal quality, stability of a perovskite with a 1.8 eV bandgap, perovskite environmental stability, and transparent electrode quality and stability.
Hyperdoping has emerged as a promising method for designing semiconductors with unique optical and electronic properties, although such properties currently lack a clear microscopic explanation. ...Combining computational and experimental evidence, we probe the origin of sub-band gap optical absorption and metallicity in Se-hyperdoped Si. We show that sub-band gap absorption arises from direct defect-to-conduction band transitions rather than free carrier absorption. Density functional theory predicts the Se-induced insulator-to-metal transition arises from merging of defect and conduction bands, at a concentration in excellent agreement with experiment. Quantum Monte Carlo calculations confirm the critical concentration, demonstrate that correlation is important to describing the transition accurately, and suggest that it is a classic impurity-driven Mott transition.
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