Silicon-Organic Heterojunction Solar Cells with Electron-Selective Contacts Based on Organic Interface Dipoles

Electron-selective contacts based on organic molecules with a permanent dipole moment are explored as an interfacial layer between n-type crystalline silicon (c-Si) and the metal electrode to modify the interface and effective work function of the contact. The amino acids histidine, tryptophan, phenylalanine, glycine, and sarcosine were investigated as dipole materials for an electron-selective contact on the back of p- and ntype c-Si with two different metal electrodes. The performance of solar cells with a boron diffusion on the front was significantly increased when histidine and/or the fluorosurfactant was applied as a full-area back surface field, resulting in conversion efficiencies of 17.5% with open-circuit voltages of 625 mV and fill factors of 76.3%. These results show the potential of organic interface dipoles for silicon organic heterojunction solar cells due to their simple formation by solution processing and their low thermal budget requirements.