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

Abstract

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.

Nonfullerene Self-Assembled Monolayers As Electron-Selective Contacts for n-i-p Perovskite Solar Cells

“…The WF of ITO/ PANDI (∼4.45 eV) is found to be lower than that of ITO/ PAAQ (∼4.66 eV), indicating a more favorable energetic alignment for electron extraction. Therefore, the larger WF difference of ITO/ PANDI (∼0.27 eV) than ITO/ PAAQ (∼0.10 eV), in reference to bare-ITO, enhances the band bending at the ITO/ PANDI /perovskite interface, thereby improving its electron selectivity (see also the schematic illustration in Figure c). , The larger shift of the WF of PANDI can be associated with its larger interface dipole compared to PAAQ , as discussed above. − Apart from WF modifications, the SAM coatings do not significantly change the surface roughness of ITO, as shown by AFM results in Figure S13.…”

“…Accordingly, we found that the net dipole moment of PAAQ at 3.94 D is smaller than that of PANDI (4.58 D). However, it is crucial to acknowledge that the net dipole moments of SAM molecules may not linearly follow the WF values, as the orientation and packing of the SAMs with respect to the ITO surface is still not fully understood. , Nevertheless, by assuming the perpendicular orientation of the SAM molecules to the substrates, the z -projection of the dipole moment becomes particularly relevant, given its higher contribution compared to the x - and y -projections. Upon calculation, we found that the z -projection dipole moment values for PAAQ and PANDI are −0.20 and −1.04 D, respectively (Figure S11 and Table S2).…”