Perovskite solar cells (PSCs) have achieved a huge success in power conversion efficiency (PCE), although they still suffer from the long-term stability problem caused by the intrinsic sensitivity of perovskites to moisture. 2,2′,7,7′-Tetrakis (N,N-dip -methoxyphenylamine) 9,9′-spirobifluorene (Spiro-OMeTAD) is widely used as the hole transport layer (HTL) in typical PSCs; meanwhile, bis(trifuoromethane)sulfonimide lithium salt (Li-TFSI) is necessary as an additive in the Spiro-OMeTAD HTL to improve the hole mobility. However, the Li + ions bring in high hygroscopicity and a water-uptake effect that both aggravate degradation of the Spiro-OMeTAD HTL and thereby of the perovskite layers. Here, we modify the Li-TFSI-based Spiro-OMeTAD HTL by adding reduced graphene oxide (rGO). We verify that rGO provides adsorption sites for Li + ions and subsequently suppresses Li + migration. The water-uptake effect originating from Li + ions is thus restrained, and unfavorable pinholes in HTL caused by Li + ion migration are eliminated. Consequently, the rGOincorporated HTL remarkably improves the device stability that maintains the initial PCEs within 3% loss after 700 h under 40% humidity; however, the pristine devices almost lose the efficiency after 620 h. In addition, the good conductivity of the rGO favors hole transport in the Spiro-OMeTAD, resulting in a promotion in PCEs from 17.7% to 19.3% by incorporating rGO in HTL. Our work takes an insight into the function of rGO in the HTL and demonstrates an effective way of improving the efficiency and stability of PSCs simultaneously.

Direct water oxidation via photocatalysis is a four-electron and multiple-proton process which requires high extra energy input to produce free dioxygen gas, making it exacting, especially under visible light irradiation. To improve the oxygen evolution reaction rates (OERs) and utilize more visible light, flower-like cobalt hydroxide/oxide (Fw-Co(OH)/Fw-CoO) photocatalysts were prepared and loaded onto graphitic carbon nitride (g-CN) by a facile coating method in this work. Influenced by the unique three-dimensional morphologies, the synthesized Fw-Co(OH) or Fw-CoO/g-CN hybrids reveal favorable combination and synergism reflected by the modified photoelectric activities and the improved OER performances. Attributed to its prominent hydrotalcite structure, Fw-Co(OH) shows better cocatalytic activity for g-CN modification compared with that of Fw-CoO. Specifically, 7 wt % Fw-Co(OH)/g-CN photocatalyst exhibits photocurrent density 4 times higher and OER performance 5 times better than pristine g-CN. This work unambiguously promotes the application of sustainable g-CN in water oxidation.

Carbon quantum dots (CQDs) have attracted tremendous interest owing to their application in bioimaging, sensors, medicine and catalysis. Herein, CQDs were prepared from several carbon sources as sensitizers for solar cells. Of the CQDs prepared, bee‐pollen‐based CQDs (B‐CQDs) achieved the highest power conversion efficiency of 0.11 % under one sun illumination (AM 1.5).

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Attempts have been made to create artificial photovoltaic (PV) devices that can harness sunlight in a clean and efficient way by mimicking natural photosynthesis process. Inspired by the role of chlorophyll in such photosynthesis, we introduced pheophytins or pyropheophytins capped carbon dots (CDs) into the dye-sensitized solar cell system. The CDs hybrids were synthesized via a single step hydrothermal treatment of celery leaf extract. The effects of hydrothermal temperature on the physical properties of CDs, and the survival rate of the natural dyes were studied. CDs heated at 120 o C (C-120) display relatively homogenous smaller particle size distribution and lower photoluminescence emission intensity relative to their counterparts obtained at higher temperatures. Heated at lower temperatures, the achieved CDs hybrids have higher amount of surviving dye molecules which would be converted into pheophytins or pyropheophytins. The nanocrystalline TiO2 solar cells based on C-120 gave the highest power conversion efficiency (PCE) of 0.48% under AM 1.5G one full sun illumination compared favorably to the average value of 0.20% normally for other biomassderived carbon dots sensitized devices. Besides functioning as light sensitizer, C-120 CDs with lower amount of trap states can also work as an effective electron transfer intermediate to improve the interaction between dye and TiO2 and suppress the photogenerated carrier recombination, thus improving solar cell performance.