EAGER: New interconnect for the perovskite-silicon tandem solar cell: optically transparent and electrically conductive multilayer film

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

A solar cell is at the heart of renewable energy devices for harvesting sun light. Out of several light absorbers for solar cells, halide perovskite is an emerging one of high performance. The power conversion efficiency (PCE) of perovskite solar cells (PSCs) is getting close to that of silicon solar cells which are dominant in a commercial market. In addition, PSCs can be manufactured using a simple and cheap synthesis process. Thus, PSCs have a potential to meet an urgent need for low cost and high efficiency power generation. However, the performance of PSCs is not expected to excel that of silicon solar cells due to a theoretical limit. A tandem solar cell consisting of PSC and Si solar cells is a promising solution to overcome such a theoretical limit. Stacks of PSC and silicon solar cell can harness solar energy much better than either PSCs or silicon solar cells. One of key components of the tandem cell is an interconnect which is placed between top PSC and bottom Si solar cells. A good interconnect needs to be electrically conductive and optically transparent. A single layer of oxide semiconductor, which is widely used as the interconnect of the tandem solar cell, does not fully meet these requirements. In this project, comprehensive research on the multilayer of semiconductor and metal films will be performed to address such a need for the interconnect of high electric conductivity and optical transparency. The new multilayer interconnect will improve the performance of the tandem solar cells and accelerate the advent of net zero economy. From the viewpoint of engineering education, the multidisciplinary aspect of this project including materials synthesis, basic science, and device fabrication will reinforce a current trend to ask future scientists and engineers to develop comprehensive knowledge and skills. Though the project, both undergraduate and graduate students will be trained in the areas of materials science, electric engineering and devices physics. Among different tandem cell designs, 2-terminal (2-T) monolithic tandem cells offers the highest PCE, because this design promotes light transmittance and suppresses parasitic resistance by reducing a number of interfaces. In addition, the 2T tandem cell simplifies the device structure and significantly reduces the production cost. However, current 2-T tandem solar cells suffer from a lack of the suitable interconnect which should provide high electric conductivity and optical transparency. This project will address this need by developing the semiconductor-metal-semiconductor (S-M-S) multilayer film. High electric carrier concentration of the central metal layer and high mobility of the semiconductor layer will be combined for the interconnect of the high electric conductivity without decreasing the transparency. The objectives of this exploratory research are 1) to develop a fundamental understanding of the physical interactions between semiconductor and metal layers in transparent conducting S-M-S films, 2) to design a novel S-M-S interconnect which selectively collects photogenerated charge carriers in PSC – silicon tandem solar cells and 3) test the new interconnect in the tandem solar cells. For these purposes, there will be extensive experimental and theoretical research on symmetric and asymmetric metal-semiconductor multilayer films to understand the electronic band structures and the light interference. Outcomes of this project (i.e. the interconnect of high electric and optical performance) will facilitate the electron-hole recombination at the interface and deliver incident to the bottom Si solar cell with minimal interface reflectance. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.