Efficient Silicon Solar Cells through Organic Self‐Assembled Monolayers as Electron Selective Contacts

• Published in: Advanced energy materials 2024-03, Vol.14 (9), p.n/a
• Main Authors: Prasetio, Adi, Pradhan, Rakesh R., Dally, Pia, Ghadiyali, Mohammed, Azmi, Randi, Schwingenschlögl, Udo, Allen, Thomas G., De Wolf, Stefaan
• Format: Article
• Language: English
• Subjects: Aluminum; Amorphous silicon; Carbazoles; crystalline silicon solar cells; Current carriers; electron‐selective contact; Energy conversion efficiency; Heterojunctions; Metal oxides; Molecular chains; Monolayers; Organic materials; Perovskites; Phosphonic acids; Photovoltaic cells; Self-assembly; self‐assembled monolayers; Silicon; Solar cells; solution‐processed; Work functions
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202303705

Effective charge carrier‐selective contacts are a crucial component of high‐performance crystalline silicon (c‐Si) solar cells. Organic materials deposited via self‐assembly on the c‐Si surface are promising candidates for simplified, scalable, and cost‐effective processing of charge extraction layers. This study investigates the application of nPACz self‐assembled monolayers (SAMs), based on carbazole and phosphonic acid groups, where n (= 2, 4, or 6) is the aliphatic chain length, to facilitate electron extraction in c‐Si solar cells by tuning the work function of aluminum (Al) at the rear contact. So far, these SAM molecules are mainly applied as the hole‐selective layer in state‐of‐the‐art perovskite and organic solar cells, via anchoring on a metal oxide electrode. Here, by inserting 2PACz between amorphous silicon passivated c‐Si and Al, an electron‐selective contact with a contact resistivity of 65 mΩ cm2 is achieved and a power conversion efficiency of 21.4% with an open‐circuit voltage of 725 mV and a fill factor of 79.2% is demonstrated. Although the 2PACz displays some instability in this study, its initial performance is comparable to those achieved with conventionally used n‐type amorphous silicon. This study highlights the potential of solution‐processable organic SAMs in forming carrier‐selective contacts for c‐Si heterojunction solar cells. [2‐(9H‐carbazol‐9‐yl)ethyl]phosphonic acid (2PACz) self‐assembled monolayers (SAMs) are utilized as electron‐selective layers in crystalline silicon (c‐Si) solar cells. These layers form chemical bonds with the silicon surface, aligning the phosphonic acid group towards the c‐Si and the carbazole group towards the alumunium (Al) electrode. This alignment creates a dipole moment, facilitating electron extraction towards the Al, and enabling efficiencies of 21.4%.