Stable Dopant-Free Asymmetric Heterocontact Silicon Solar Cells with Efficiencies above 20%
Development of new device architectures and process technologies is of tremendous interest in crystalline silicon (c-Si) photovoltaics to drive enhanced performance and/or reduced processing cost. In this regard, an emerging concept with a high-efficiency potential is to employ low/high work function metal compounds or organic materials to form asymmetric electron and hole heterocontacts. This Letter demonstrates two important milestones in advancing this burgeoning concept. First, a high-performance, low-temperature, electron-selective heterocontact is developed, comprised of a surface passivating a-Si:H layer, a protective TiOx interlayer, and a low work function LiFx/Al outer electrode. This is combined with a MoOx hole-selective heterocontact to demonstrate a cell efficiency of 20.7%, the highest value for this cell class to date. Second, we show that this cell passes a standard stability test by maintaining >95% of its original performance after 1000 h of unencapsulated damp heat exposure, indicating its potential for longevity. ; Materials characterization was supported by the Electronic Materials Programs, funded by the Director, Office of Science, Office of Basic Energy Sciences, Material Sciences and Engineering Division of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. XPS characterization was performed at the Joint Center for Artificial Photosynthesis, supported through the Office of Science of the U.S. Department of Energy under Award Number DESC0004993. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy (Contract No. DE-AC02- 05CH11231). S.E. held a Marie Skłodowska-Curie Individual Fellowship from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No: 706744, action acronym: COLIBRI). Work at EPFL was financially supported by the Swiss National Science Foundation via the NRP70 "Energy Turnaround" Project "PV2050". Work at the ANU was supported by the Australian Government through the Australian Research Council (Discovery Project: DP150104331) and the Australia−US Institute for Advanced Photovoltaics (AUSIAPV) program under Grant Number ACAP6.9.