penghuang

Triarylamine-based polymers with different functional groups were synthetized as hole-transport materials (HTMs) for perovskite solar cells (PSCs). The novel materials enabled efficient PSCs without the use of chemical doping (or additives) to enhance charge transport. Devices employing poly(triarylamine) with methylphenylethenyl functional groups (V873) showed a power conversion efficiency of 12.3 %, whereas widely used additive-free poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) demonstrated 10.8 %. Notably, devices with V873 enabled stable PSCs under 1 sun illumination at maximum power point tracking for approximately 40 h at room temperature, and in the dark under elevated temperature (85 °C) for more than 140 h. This is in stark contrast to additive-containing devices, which degrade significantly within the same time frame. The results present remarkable progress towards stable PSC under real working conditions and industrial stress tests.

PolyTPAs for stable PSCs: Poly(triarylamine) with methylphenylethenyl functional groups (V873) is used as a hole-transporting material in perovskite solar cells (PSCs). Devices employing V873 reach a power conversion efficiency of 12.3 % without any additives, and enable stable operation under 1 sun at maximum power point tracking and under elevated temperature (85 °C). This result shows remarkable progress towards stable PSCs under real working conditions and industrial stress tests.

The solution processing of pinhole-free methylammonium lead triiodide perovskite–C₇₀ fullerene (MAPbI₃:C₇₀) blend films on fluorine-doped tin oxide (FTO)-coated glass substrates is presented. Based on this approach, a simplified and robust protocol for the preparation of efficient electron-transport layer (ETL)-free perovskite solar cells is described. Power conversion efficiency (PCE) of 13.6 % under AM 1.5 G simulated sunlight is demonstrated for these devices. Comparative impedance spectroscopy and photostability analysis of the MAPbI₃:C₇₀ and single MAPbI₃ films compared with conventional compact TiO₂ ETL-based devices are shown. The beneficial impact of using MAPbI₃:C₇₀ blend films is emphasized.

Mix, spin, go! Perovskite solar cells based on pinhole-free perovskite–C₇₀ fullerene blend films deposited on fluorine-doped tin oxide (FTO)-coated glass substrates, without a specific electron-transporting/blocking layer, are fabricated and characterized. Enhanced photovoltaic performance and stability with respect to traditional compact TiO₂-based cells is achieved for these simplified devices under continuous AM 1.5 G simulated sunlight, without the need for encapsulation.

Organic–inorganic hybrid perovskite light absorbers have recently emerged as a “holy grail” for next generation thin-film photovoltaics with excellent optoelectronics properties and low fabrication cost. In a very short span of time, we have witnessed a pronounced and unexpected progress in organic– inorganic perovskite solar cells (PSCs) with a vertical rise in power conversion efficiency from 3.8 to 22.1 %. In this manuscript we focus specifically on the recent development of metal oxide-based electron-transporting layer (ETL) modification for high performing PSCs and their stability. This review highlights various methodologies to modify existing compact/scaffold layers for improving device performance and stability. Various aspects of the ETL are discussed with different metal oxide compact layers in their relation to modification in mesoporous layers towards the design of a cell structure with high performance and stability.

Dig deeper–Solution at the bottom! Recent developments of metal oxide-based electron-transporting layers (ETLs) for high performing, stable perovskite solar cells (PSCs) are reviewed. Various methodologies to modify existing ETLs, the first deposited layer in regular architecture PSCs, are highlighted, and the effects of these modifications are considered towards the design of a cell structure with high performance and stability.

Three novel hole-transporting materials (HTMs) using the 4-methoxytriphenylamine (MeOTPA) core were designed and synthesized. The energy levels of the HTMs were tuned to match the perovskite energy levels by introducing symmetrical electron-donating groups linked with olefinic bonds as the π bridge. The methylammonium lead triiodide (MAPbI₃) perovskite solar cells based on the new HTM Z34 (see main text for structure) exhibited a remarkable overall power conversion efficiency (PCE) of 16.1 % without any dopants or additives, which is comparable to 16.7 % obtained by a p-doped 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD)-based device fabricated under the same conditions. Importantly, the devices based on the three new HTMs show relatively improved stability compared to devices based on spiro-OMeTAD when aged under ambient air containing 30 % relative humidity in the dark.

Stability in 3 Ds: Three dopant-free donor (D)–π–D–π–D conjugated hole-transport materials (HTMs) with tunable energy levels are developed for perovskite solar cells exhibiting excellent power conversion efficiency up to 16.1 %, which is comparable to devices with the state-of-art doped HTM (spiro-OMeTAD). Moreover, the devices based on these three HTMs are more stable than spiro-OMeTAD-based devices in ambient air.

In this report, we fabricated thiocyanate-based perovskite solar cells with low-pressure vapor-assisted solution process (LP-VASP) method. Photovoltaic performances are evaluated with detailed materials characterizations. Scanning electron microscopy images show that SCN-based perovskite films fabricated using LP-VASP have long-range uniform morphology and large grain sizes up to 1 μm. The XRD and Raman spectra were employed to observe the characteristic peaks for both SCN-based and pure CH₃NH₃PbI₃ perovskite. We observed that the Pb(SCN)₂ film transformed to PbI₂ before the formation of perovskite film. X-ray photoemission spectra (XPS) show that only a small amount of S remained in the film. Using LP-VASP method, we fabricated SCN-based perovskite solar cells and achieved a power conversion efficiency of 12.72 %. It is worth noting that the price of Pb(SCN)₂ is only 4 % of PbI₂. These results demonstrate that pseudo-halide perovskites are promising materials for fabricating low-cost perovskite solar cells.

Pseudohalide, solid performance: Pseudohalide SCN-based perovskite layers are fabricated using the low-pressure vapor-assisted solution processing method. The formation mechanism, full characterization of the films, and the SCN/I ratio in the final perovskite films are investigated. Devices fabricated using these films yielded power conversion efficiency values of 12.72 % with nearly 90 % of the initial PCE maintained after a 10 day stability test.

Organic–inorganic halide perovskite solar cells have attracted great attention because of their superb efficiency reaching 22 % and low-cost, facile fabrication processing. Nevertheless, stability issues in perovskite solar cells seem to block further advancements toward commercialization. Thus, device stability is one of the important topics in perovskite solar cell research. In the beginning, the poor moisture resistivity of the perovskite layer was considered as a main problem that hindered further development of perovskite solar cells, which encouraged engineering of the perovskite or protection of the perovskite by a buffer layer. Soon after, other parameters affecting long-term stability were sequentially found and various attempts have been made to enhance intrinsic and extrinsic stability. Here we review the recent progresses addressing stability issues in perovskite solar cells. In this report, we investigated factors affecting stability from material and device points of view. To gain a better understanding of the stability of the bulk perovskite material, decomposition mechanisms were investigated in relation to moisture, photons, and heat. Stability of full device should also be carefully examined because its stability is dependent not only on bulk perovskite but also on the interfaces and selective contacts. In addition, ion migration and current–voltage hysteresis were found to be closely related to stability.

Between the layers: The stability of perovskite solar cells and the research involved to overcome this challenge through optimization of the perovskite material and charge-selective layers is reviewed in detail. The most dominant factor affecting stability of halide perovskite is moisture, which induces even faster degradation when it was coupled with light and heat. The stability issues in perovskite solar cells are expected to be solved as we gain better understanding of the factors and the mechanisms on the instability of perovskite solar cells.