Highly Stable and Efficient N-I-P Structured Tin-Rich Lead-Tin Halide Perovskite Solar Cells with Blended Hole-Transporting Materials

Mixed lead-tinv halide (LTH) perovskite solar cells (LTH-PSCs) can reduce the toxicity concerns of full lead-based PSCs and potentially optimize the bandgap to maximize efficiency. However, commonly used hole-transporting material (HTM) 2,2 ',7,7 '-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9 '-spirobifluorene (Spiro-OMeTAD) with additional dopants Li-bis(trifluoromethanesulfonyl) imide (Li-TFSI) and 4-tert-butylpyridine (t-BP) deteriorate oxidation Sn2+ to Sn4+ leading to trap formation. Here, the study introduces a novelty Sn-friendly HTM for Sn-rich LTH-PSCs, combining Spiro-OMeTAD with 4-Isopropyl-4 '-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (dpi-TPFB) as a dopant and blended with poly(3-hexylthiophene-2,3-diyl) (P3HT). This blended HTM avoids the harmful effects of Li-TFSI and t-BP dopants and leverages the beneficial hydrophobic properties of P3HT, which predominantly resides on the surface with a face-on orientation. This arrangement not only enhances charge transport and extraction but also improves device stability by protecting the perovskite from environmental factors. Optimizing the P3HT concentration of blended HTM achieved a PCE of 17.27%, the highest reported for n-i-p structured Sn-rich mixed LTH-PSCs. This HTM also significantly improved device stability, maintaining over 90% of the initial PCE after 3000 h of storage and 80% under maximum power point tracking (MPPT) for 550 h in the air.