Perovskite Solar Cell Using Isonicotinic Acid as a Gap-Filling Self-Assembled Monolayer with High Photovoltaic Performance and Light Stability

High photovoltaic performance and light stability arerequiredfor the practical outdoor use of lead-halide perovskite solar cells.To improve the light stability of perovskite solar cells, it is effectiveto introduce a self-assembled monolayer (SAM) between the carriertransport layer and the perovskite layer. Several alternative approachesin their molecular design and combination with multiple SAMs supporthigh photovoltaic conversion efficiency (PCE). Herein, we report anew structure for improving both PCE and light stability, in whichthe surface of an electron transport layer (ETL) was modified by combininga fullerene-functionalized self-assembled monolayer (C(60)SAM) and a suitable gap-filling self-assembled monolayer (GFSAM).Small-sized GFSAMs can enter the gap space of the C(60)SAMand terminate the unterminated sites on the ETL surface. The bestGFSAM in this study was formed using an isonicotinic acid solution.After a light stability test for 68 h at 50 & DEG;C under 1 sun illumination,the best cell with C(60)SAM and GFSAM showed a PCE of 18.68%with a retention rate of over 99%. Moreover, following outdoor exposurefor six months, the cells with C(60)SAM and GFSAM exhibitedalmost unchanged PCE. From the valence band spectra of the ETLs obtainedusing hard X-ray photoelectron spectroscopy, we confirmed a decreasein the offset at the ETL/perovskite interface owing to the additionalGFSAM treatment on the C(60)SAM-modified ETL surface. Time-resolvedmicrowave conductivity measurements demonstrated that the additionalGFSAM improved electron extraction at the C(60)SAM-modifiedETL/perovskite interface.

Automated summary

To enhance the light stability of lead-halide perovskite solar cells, a self-assembled monolayer (SAM) is introduced between the carrier transport layer and the perovskite layer. By combining a fullerene-functionalized SAM (C(60)SAM) and a suitable gap-filling SAM (GFSAM), both the photovoltaic conversion efficiency (PCE) and light stability are improved. The best cell with C(60)SAM and GFSAM exhibits a PCE of 18.68% and a retention rate of over 99% after a light stability test, and shows almost unchanged PCE after six months of outdoor exposure.