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

Single-isomer bis(pyrrolidino)fullerenes as electron-transporting materials for tin halide perovskite solar cells

Although fullerene bisadducts are promising electron-transporting materials for tin halide perovskite solar cells, they are generally synthesized as a mixture of isomeric products that require a complicated separation process. Here, we introduce a phenylene-bridged bis(pyrrolidino)fullerene, Bis-PC, which forms only a single isomer due to geometrical restriction. When used in a tin perovskite solar cell with a PEA0.15FA0.85SnI3 (PEA: phenylethylammonium and FA: formamidinium) light absorption layer, the resulting open-circuit voltage (V OC) was 0.78 V, a value higher than that of fullerene monoadducts and comparable to that of the commonly used indene-C60 bisadduct (ICBA). The performance could be further improved by the composition engineering of perovskite, where the PEA0.15(FA0.87MA0.13)0.85SnI3 based device (MA: methylammonium) exhibited a photoelectric conversion efficiency of 12.3% with a V OC of 0.86 V. The device with single-isomer Bis-PC shows superior stability to that with mixed-isomer ICBA, retaining its initial performance after 3000 h storage under an inert atmosphere.

Adjusting the Crystallization of Tin Perovskites through Thiophene Additives for Improved Photovoltaic Stability

Tin-based perovskites (Sn-PVK) are promising lead-free alternatives for efficient photovoltaic technology, but they face challenges related to bulk and surface defects due to suboptimal crystallization and Sn2+ oxidation. Introducing thiophene-2-ethylammonium halides (TEAX, where X = I, Br, Cl) improves FASnI3 crystallization and reduces Sn4+ formation. This is achieved by adjusting the crystallization dynamics through the formation of a complex between S and Sn during the preparation of the precursor solution, which also inhibits Sn2+ oxidation in the resulting films. In solar cells, these additives boost power conversion efficiency (PCE) from 6.6% (without additives) to 9.4% (using TEABr), with further enhancement to 12% by adjusting selective contacts. The addition of TEAX also increases the Sn2+ content, outperforming control. Devices with TEABr maintained over 95% of their initial PCE after 2000 h in N2 under continuous operation with 1 sun simulated illumination.

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.