Advanced doped‐silicon‐layer‐based passivating contacts have boosted the power conversion efficiency (PCE) of single‐junction crystalline silicon (c‐Si) solar cells to over 26%. However, the inevitable parasitic light absorption of the doped silicon layers impedes further PCE improvement. To this end, alternative passivating contacts based on wide‐bandgap metal compounds (so‐called dopant‐free passivating contacts (DFPCs)) have attracted great attention, thanks to their potential merits in terms of parasitic absorption loss, ease‐of‐deposition, and cost. Intensive research activity has surrounded this topic with significant progress made in recent years. Various electron‐selective and hole‐selective contacts based on metal compounds have been successfully developed, and a champion PCE of 23.5% has been achieved for a c‐Si solar cell with a MoOx‐based hole‐selective contact. In this work, the fundamentals and development status of DFPCs are reviewed and the challenges and potential solutions for enhancing the carrier selectivity of DFPCs are discussed. Based on comprehensive and in‐depth analysis and simulations, the improvement strategies and future prospects for DFPCs design and device implementation are pointed out. By tuning the carrier concentration of the metal compound and the work function of the capping transparent electrode, high PCEs over 26% can be achieved for c‐Si solar cells with DFPCs.

Progress and Future Prospects of Wide‐Bandgap Metal‐Compound‐Based Passivating Contacts for Silicon Solar Cells

Solar cells rely on the efficient generation of electrons and holes and the subsequent collection of these photoexcited charge carriers at spatially separated electrodes. High wafer quality is now commonplace for crystalline silicon (c‐Si) based solar cells, meaning that the cell's efficiency potential is largely dictated by the effectiveness of its carrier‐selective contacts. The majority of contacts currently employed in industrial production are based on highly doped‐silicon, which can introduce negative side‐effects including Auger recombination or parasitic absorption depending on whether the dopants are diffused into the absorber or whether they are incorporated into silicon layers deposited outside the absorber. Given the terawatt scale of deployment of c‐Si solar cells, the search for alternative contacting schemes that can offer potential benefits in terms of performance, cost, ease of processing or stability is highly relevant. One such category of contacting schemes, with the potential to avoid the above mentioned issues, is that which employs metal compounds as the ‘carrier‐selective’ layer. The last 7 years has seen a surge in interest on this topic and a few promising families of materials have emerged, most prominently the alkali/alkaline‐earth metal compounds and the transition‐metal oxides. The number of successful selective‐contact demonstrations of materials within these families is fast increasing with the best solar cell demonstrations now exceeding 23%. However, in addition to improving their efficiency performance, several challenges remain if such contacts are to be considered for industrial adoption. These are mainly associated with poor stability, lack of compatibility with transparent electrodes and inability to be deposited using standard industrial techniques. This review covers the historical developments, current status and future prospects of metal‐compound based selective contacts in the context of c‐Si photovoltaics.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/pip.3552

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Zhiming Chen

Papers

Degradation Mechanism and Stability Improvement of Dopant-Free ZnO/LiFx/Al Electron Nanocontacts in Silicon Heterojunction Solar Cells

Green-laser-doped selective emitters with separate BBr3 diffusion processes for high-efficiency n-type silicon solar cells

Yttrium Fluoride-Based Electron-Selective Contacts for Crystalline Silicon Solar Cells

High-Performance Europium Fluoride Electron-Selective Contacts for Efficient Crystalline Silicon Solar Cells

Enhanced Hole Extraction of WOx/V2Ox Dopant‐Free Contact for p‐type Silicon Solar Cell