As single junction thin-film technologies, both Si heterojunction (HIT) and Perovskite based solar cells promise high efficiencies at low cost. One expects that a tandem cell design with these cells connected in series will improve the efficiency further. Using a self-consistent numerical modeling of optical and transport characteristics, however, we find that a traditional series connected tandem design suffers from low due to band-gap mismatch and current matching constraints. It requires careful thickness optimization of Perovskite to achieve any noticeable efficiency gain. Specifically, a traditional tandem cell with state-of-the-art HIT () and Perovskite ( ) sub-cells provides only a modest tandem efficiency of 25%. Instead, we demonstrate that a bifacial HIT/Perovskite tandem design decouples the optoelectronic constraints and provides an innovative path for extraordinary efficiencies. In the bifacial configuration, the same state-of the-art sub-cells achieve a normalized output of =33%, exceeding the bifacial HIT performance at practical albedo reflections. Unlike the traditional design, this bifacial design is relatively insensitive to Perovskite thickness variations, which may translate to simpler manufacture and higher yield.

a-Si/c-Si (amorphous Silcon/crystalline Silicon) heterojunction solar cells exhibit several distinctive dark and light I-V nonideal features. The dark I-V of these cells exhibits unusually high ideality factors at low forward-bias and the occurrence of a "knee" at medium forward-bias. Nonidealities under illumination, such as the failure of superposition and the occurrence of an "S-type" curve, are also reported in these cells. However, the origin of these nonidealities and how the dark I-V nonidealities manifest themselves under illumination, and vice versa, have not been clearly and consistently explained in the current literature. In this study, a numerical framework is used to interpret the origin of the dark I-V nonidealities, and a novel simulation technique is developed to separate the photo-current and the contact injection current components of the light I-V. Using this technique, the voltage dependence of photo-current is studied to explain the failure of the superposition principle and the origin of the S-type light I-V characteristics. The analysis provides a number of insights into the correlations between the dark I-V and the light I-V. Finally, using the experimental results from this study and from the current literature, it is shown that these nonideal effects indeed affect the dark I-V and the light I-V in a predictable manner.

The device physics of commercially dominant diffused-junction silicon solar cells is well understood, allowing sophisticated optimization of this class of devices. Recently, so-called passivating-contact solar cell technologies have become prominent, with Kaneka setting the world's silicon solar cell efficiency record of 26.63% using silicon heterojunction contacts in an interdigitated configuration. Although passivating-contact solar cells are remarkably efficient, their underlying device physics is not yet completely understood, not in the least because they are constructed from diverse materials that may introduce electronic barriers in the current flow.To bridge this gap in understanding, we explore the device physics of passivating contact silicon heterojunction (SHJ) solar cells. Here, we identify the key properties of heterojunctions that affect cell efficiency, analyze the dependence of key heterojunction properties on carrier transport under light and dark conditions, provide a self-consistent multiprobe approach to extract heterojunction parameters using several characterization techniques (including dark J-V, light J-V, C-V, admittance spectroscopy, and Suns-Voc), propose design guidelines to address bottlenecks in energy production in SHJ cells, and develop a process-to-module modeling framework to establish the module's performance limits. We expect that our proposed guidelines resulting from this multiscale and self-consistent framework will improve the performance of future SHJ cells as well as other passivating contact-based solar cells.

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