Tetrahedrite (Cu12Sb4S13) Ternary Inorganic Hole Conductor for Ambient Processed Stable Perovskite Solar Cells

Abstract

The hole transport layer (HTL) in a solar cell is a key component for the optimization of photon to electron conversion efficiency and long-term device stability. So far, organic hole transport (HT) materials have been extensively used in mesoscopic perovskite (n–i–p) solar cells for achieving high efficiency. Generally, organic hole transporters are expensive and exhibit low chemical stability. This often results in rapid degradation in the photon to electron conversion efficiencies. In this report, copper antimony sulfide (CAS, Cu12Sb4S13) tetrahedrite crystal phase nanoparticles capped with organic ligands are synthesized using a simple hot injection method. The ternary semiconductor nanoparticles exhibit high carrier concentration (3.4 × 1018 cm–3) and electrical conductivity (0.043 Ω cm) with respect to the conventionally used organic HT, e.g., spiro-OMeTAD. Additionally, appropriate conduction band and valence band positions in the CAS nanoparticles assist in efficient separation of the photogenerated holes from the perovskite materials and block the electrons from moving transport toward the counter metal contact. Incorporation of CAS in the MAPbI3 perovskite solar cell as an HTL, assembled using an ambient fabrication process, achieves a power conversion efficiency of approximately 6.5%. The efficiency degradation studied under controlled humidity (<70%) conditions exhibited a slower rate of decrease for the MAPbI3–CAS (85% and 50% on the 4th and 15th day) compared to the MAPbI3-spiro solar cell (10% on the fourth day). The chemical stability and solar cell performance are attributed to the synergetic effect of crystal phase stability and hydrophobic nature of the organic ligand capped CAS HTL layer. This leads to high moisture resistance and nullifies the need for an additional encapsulation layer as demonstrated in reported literature studies.