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

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 m omega 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%.image