Ultrathin Poly(3-hexylthiophene) Nanowires as Chemically Robust and Versatile Surface Passivators of Perovskite Solar Absorbers

Abstract

Surface passivation of perovskite solar absorbers is essential for improving device performance and stability. Various defects, such as ionic vacancies and grain boundaries, serve as charge-trapping sites. Suppressing charge recombination through passivation promotes carrier injection/transfer at the interfaces between the perovskite and charge transport layers (CTLs). However, during the fabrication of solar cells, the passivation layers can be damaged during the spin coating of the solutions for the deposition of CTLs. Organic semiconducting passivators can dissolve in nonpolar solvents. Passivators with a high resistance to dissolution in these solutions are necessary to preserve the passivated perovskite surface. In this study, poly(3-hexylthiophene) nanowires (P3HT-NWs) were used to achieve sustainable surface passivation. They were synthesized by cooling P3HT/m-xylene solutions. Ultrathin P3HT-NW layers (2.5 nm thick) uniformly cover the perovskite surface. The lone pair electrons of the thiophene backbones readily coordinate with Pb2+, leading to a significant reduction in the defect density. The band alignment of perovskite and 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifluorene (spiro-OMeTAD), which was improved by incorporating P3HT-NW layers, facilitated carrier injection/transfer at their interfaces. The highly crystalline and robust P3HT-NW films remained intact during the spin-coating of the spiro-OMeTAD solutions. The resulting power conversion efficiency (PCE) increased significantly from 18.89% to 20.49%. Furthermore, the normalized PCE of the unencapsulated device was retained at 81.7% of its initial value after 1000 h under 1 sun illumination because the hydrophobic P3HT-NW layers effectively protected the perovskite against moisture.