Interface engineering is critical to the development of highly efficient perovskite solar cells. Here, urea treatment of hole transport layer (e.g., poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS)) is reported to effectively tune its morphology, conductivity, and work function for improving the efficiency and stability of inverted MAPbI 3 perovskite solar cells (PSCs). This treatment has significantly increased MAPbI 3 photovoltaic performance to 18.8% for the urea treated PEDOT:PSS PSCs from 14.4% for pristine PEDOT:PSS devices. The use of urea controls phase separation between PEDOT and PSS segments, leading to the formation of a unique fiber-shaped PEDOT:PSS film morphology with well-organized charge transport pathways for improved conductivity from 0.2 S cm −1 for pristine PEDOT:PSS to 12.75 S cm −1 for 5 wt% urea treated PEDOT:PSS. The urea-treatment also addresses a general challenge associated with the acidic nature of PEDOT:PSS, leading to a much improved ambient stability of PSCs. In addition, the device hysteresis is significantly minimized by optimizing the urea content in the treatment.order to overcome the reactivity issue of the acidic PEDOT:PSS with the plastic substrates. Therefore, we expect this technology to be expanded for addressing the stability and performance issues of perovskite solar cells.

Low-temperature processed inorganic hole transport layer for efficient and stable mixed Pb-Sn low-bandgap perovskite solar cells

In this work, methylammonium lead triiodide (CH3NH3PbI3) perovskite solar cells with efficiencies higher than 18% were achieved using a new nanocomposite hole transport layer (HTL) by doping poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with a mixed dopant of polyaniline (PANI) and graphene oxide (GO). A synergistic engineering between GO, PANI, and PEDOT:PSS was accomplished to introduce additional energy levels between perovskite and PEDOT:PSS and increase the conductivity of PEDOT:PSS. Kelvin probe force microscope results confirmed that adding GO to PEDOT:PSS/PANI composite significantly reduced the average surface potential. This increased the open circuit voltage (Voc) to 1.05 V for the GO/PEDOT:PSS/PANI nanocomposite perovskite solar cells from the pristine PEDOT:PSS (Voc = 0.95 V) and PEDOT:PSS/PANI (Voc = 0.99 V). In addition, adding PANI to the HTLs substantially enhanced short circuit current density (Jsc). This was supported by the current sensing‐atomic force microscopy (CS‐AFM) and conductivity measurements. The PANI doped films showed superior electrical conductivity compared with those without PANI as indicated by CS‐AFM results. PANI can fill the gaps between the microflakes of GO and give rise to more compact hole transport material (HTM) layer. This led to a higher Jsc after doping with PANI, which was consistent with the incident photon‐to‐current efficiency and electrochemical impedance spectroscopy results. The results of X‐ray diffraction (XRD) and AFM indicated the GO/PANI doped HTMs significantly improved the crystallinity, topography, and crystal size of the perovskite film grown on their surface. A higher efficiency of 18.12% for p‐i‐n perovskite solar cells has been obtained by adding the mixed dopant of GO, PANI, and PEDOT:PSS, demonstrating better stability than the pristine PEDOT:PSS cell.image

It has been a challenge to use transition metal oxides as anode materials in Li-ion batteries due to their low electronic conductivity, poor rate capability and large volume change during charge/discharge processes. Here, we present the first demonstration of a unique self-recovery of capacity in transition metal oxide anodes. This was achieved by reducing tungsten trioxide (WO3) via the incorporation of urea, followed by annealing in a nitrogen environment. The reduced WO3 successfully self-retained the Li-ion cell capacity after undergoing a sharp decrease upon cycling. Significantly, the reduced WO3 also exhibited excellent rate capability. The reduced WO3 exhibited an interesting cycling phenomenon where the capacity was significantly self-recovered after an initial sharp decrease. The quick self-recoveries of 193.21%, 179.19% and 166.38% for the reduced WO3 were observed at the 15th (521.59/457.41 mA h g-1), 36th (538.49/536.61 mA h g-1) and 45th (555.39/555.39 mA h g-1) cycles respectively compared to their respective preceding discharge capacity. This unique self-recovery phenomenon can be attributed to the lithium plating and conversion reaction which might be due to the activation of oxygen vacancies that act as defects which make the WO3 electrode more electrochemically reactive with cycling. The reduced WO3 exhibited a superior electrochemical performance with 959.1/638.9 mA h g-1 (1st cycle) and 558.68/550.23 mA h g-1 (100th cycle) vs. pristine WO3 with 670.16/403.79 mA h g-1 (1st cycle) and 236.53/234.39 mA h g-1 (100th cycle) at a current density of 100 mA g-1.