Tin Halide Perovskite Solar Cells with Open-Circuit Voltages Approaching the Shockley-Queisser Limit

An open-cage bis[60]fulleroid as an electron transport material for tin halide perovskite solar cells

An open-cage bis[60]fulleroid (OC) was applied as an electron transport material (ETM) in tin (Sn) halide perovskite solar cells (PSCs). Due to the reduced offset between the energy levels of Sn-based perovskites and ETMs, the power conversion efficiency (PCE) of Sn-based PSCs with OC reached 9.6% with an open-circuit voltage (VOC) of 0.72 V. Additionally, OC exhibited superior thermal stability and provided 75% of the material without decomposition after vacuum deposition. The PSC using vacuum-deposited OC as the ETM could afford a PCE of 7.6%, which is a big leap forward compared with previous results using vacuum-deposited fullerene derivatives as ETMs.

Evaporable Fullerene Indanones with Controlled Amorphous Morphology as Electron Transport Layers for Inverted Perovskite Solar Cells

Fullerenes are among the most commonly used electron-transporting materials (ETMs) in inverted perovskite solar cells (IPSCs). Although versatile functionalized fullerene derivatives have shown excellent performance in IPSCs, pristine [60]fullerene (C60) is still the most widely used in devices mainly because of its uniform morphology by thermal deposition. However, thermally evaporable fullerene derivatives have not yet been achieved. Herein, we developed a series of evaporable fullerene derivatives, referred to as fullerene indanones (FIDOs), affording IPSCs with high power conversion efficiency (PCE) and long-term storage stability. The FIDOs were designed with a unique architecture in which the fullerene moiety and a benzene ring moiety are linked via a five-membered carbon ring in benzene ring plane. This molecular arrangement affords exceptional thermal stability, allowing the FIDOs to withstand harsh thermal deposition conditions. Moreover, by manipulating the steric bulk of the functional groups, we could control the state of the organic film from crystalline to amorphous. Subsequently, we used FIDOs as an electron transport layer (ETL) in IPSCs. Thanks to the suitable energy level and dual-passivation effect of FIDOs compared with a reference ETL using C60, the device using FIDOs achieved an open-circuit voltage of 1.16 V and a fill factor of 0.77. As a result, the PCE reached 22.11%, which is superior to 20.45% of the best-performing reference device. Most importantly, the FIDO-based IPSC devices exhibited exceptional stability in comparison to the reference device due to the stability of the amorphous ETL films.