A research team led by Prof. WANG Mingtai from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has proposed an interesting approach to improve the efficiency of solar cells. Their focus on the potential antimony trisulfide (Sb₂S₃) as a photovoltaic absorber has led to a Parallel Planar Heterojunction (PPHJ) strategy for fabricating highly efficient solar cells.

Their results have been published in Angewandte Chemie International Edition.

One of the current challenges to the terrestrial use of photovoltaic electricity is the lack of inexpensive, efficient, and stable materials and related photovoltaic devices for converting photons into electrons. Typically, two independent planar heterojunction (PHJ) subcells are stacked in tandem to create efficient solar cells. However, the need for an interfacial layer to recombine the opposite charges of the top and bottom subcells adds complexity to material selection and device preparation.

"This is why we introduced the PPHJ strategy in our study," said team member Prof. CHEN Chong, “it enables us to realize the practical potential of creating efficient multiple PHJ solar cells."

The Sb₂S₃-based PPHJ device consists of two types of conventional PHJ subcells connected in parallel. The researchers explained the divided tasks. The Sb₂S₃-based PHJ subcells are responsible for absorption and charge generation, while the CH₃NH₃PbI₃-based PHJ subcells control the electron transport to the collection electrode. Despite the two types of subcells, the PPHJ device remains a Sb₂S₃ device in nature.

The result is a remarkable increase in the efficiency of solution-processed Sb₂S₃ solar cells, achieving an impressive 8.32% efficiency, the highest among all Sb₂S₃ devices.

"In fact, our strategy simplifies the preparation process by allowing for the conventional sequential deposition of multiple PHJ layers," said CHEN, "It eliminates the typical complexity associated with both tandem and parallel tandem PHJ systems."

"This study paves the way for the conceptual design of low-cost and efficient partially or fully inorganic solar cells, thus promoting their development," said CHEN.

The architecture, photovoltaic performance and carrier process in the Sb₂S₃-based PPHJ solar cell. (Image by the team)