Dikai Xu

Ambient Engineering for High-Performance Organic–Inorganic Perovskite Hybrid Solar Cells

Considering the evaporation of solvents during fabrication of perovskite films, the organic ambience will present a significant influence on the morphologies and properties of perovskite films. To clarify this issue, various ambiences of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and chlorobenzene (CBZ) are introduced during fabrication of perovskite films by two-step sequential deposition method. The results reveal that an ambient CBZ atmosphere is favorable to control the nucleation and growth of CH3NH3PbI3 grains while the others present a negative effect. The statistical results show that the average efficiencies of perovskite solar cells processed in an ambient CBZ atmosphere can be significantly improved by a relatively average value of 35%, compared with those processed under air. The efficiency of the best perovskite solar cells can be improved from 10.65% to 14.55% by introducing this ambience engineering technology. The CH3NH3PbI3 film with large-size grains produced in an ambient CBZ atmosphere can effectively reduce the density of grain boundaries, and then the recombination centers for photoinduced carriers. Therefore, a higher short-circuit current density is achieved, which makes main contribution to the improvement in efficiency. These results provide vital progress toward understanding the role of ambience in the realization of highly efficient perovskite solar cells.

Interface engineering and efficiency improvement of monolayer graphene-silicon solar cells by inserting an ultra-thin LiF interlayer

Graphene–silicon (Gr–Si) Schottky junction solar cells have recently attracted intensive attention as candidates for low-cost photovoltaic devices. However, the efficiency of Gr–Si solar cells still needs further improvement. In this study, we have introduced an ultra-thin LiF layer between the Si and aluminum (Al) back electrode of Gr–Si solar cells. It is found that carrier recombination at the back surface is significantly suppressed, resulting directly in the improvement of external quantum efficiency (EQE) of devices in the long wavelength range of 800–1100 nm. Moreover, the back contact resistance is greatly reduced, and therefore the fill factor (FF) of devices is greatly improved. As a result, the highest power conversion efficiency (PCE) of 6.25% has been obtained for a pristine Gr–Si solar cell, which is further improved to 10.61% after chemical doping. These results pave a new way to the fabrication of high efficiency Gr–Si solar cells.

Fulleropyrrolidinium Iodide As an Efficient Electron Transport Layer for Air-Stable Planar Perovskite Solar Cells

Organic-inorganic halide perovskite solar cells have attracted great attention in recent years. But there are still a lot of unresolved issues related to the perovskite solar cells such as the phenomenon of anomalous hysteresis characteristics and long-term stability of the devices. Here, we developed a simple three-layered efficient perovskite device by replacing the commonly employed PCBM electrical transport layer with an ultrathin fulleropyrrolidinium iodide (C60-bis) in an inverted p-i-n architecture. The devices with an ultrathin C60-bis electronic transport layer yield an average power conversion efficiency of 13.5% and a maximum efficiency of 15.15%. Steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements show that the high performance is attributed to the efficient blocking of holes and high extraction efficiency of electrons by C60-bis, due to a favorable energy level alignment between the CH3NH3PbI3 and the Ag electrodes. The hysteresis effect and stability of our perovskite solar cells with C60-bis become better under indoor humidity conditions.

Room-temperature processed, air-stable and highly efficient graphene/silicon solar cells with an organic interlayer

Graphene/silicon (Gr/Si) solar cells have attracted interest for their potential in low-cost photovoltaic applications. Inserting a p-type organic hole transporting layer (HTL) in-between the Gr and Si would suppress carrier recombination and improve the performance of the solar cells. Here, we report highly stable and high-performance Gr/Si solar cells fabricated by using a room-temperature process. Spiro-OMeTAD was selected as the HTL for its novel electrical and optical properties. The employment of spiro-OMeTAD led to an impressive power conversion efficiency (PCE) of 13.02%. Moreover, our solar cells exhibit excellent stability with a PCE of ∼11% for over four months. These results could be encouraging for the development of Gr/Si solar cells toward practical applications. Meanwhile, this work offers a universal solution for the application of organics in Gr-based optoelectronics and photovoltaics from the viewpoint of device robustness.

Self-generation of a quasi p–n junction for high efficiency chemical-doping-free graphene/silicon solar cells using a transition metal oxide interlayer

Graphene/silicon (Gr/Si) solar cells have attracted extensive research interest for their potentials in low-cost photovoltaic applications. However, the performance of Gr/Si solar cells is still limited by the working principles of Schottky junctions. This work developed a new type of Gr/Si solar cell with a self-generated quasi p–n junction. In such devices, a strong upward band bending is caused by considerable charge transfer from Si, resulting in a p-type layer being formed at the near-surface of the n-type Si substrate. They have similar rectification characteristics to conventional p–n junctions, and are even superior due to the absence of the “dead layer”. Here, a thermal evaporation deposited tungsten tri-oxide (WO3) interlayer was inserted between the Gr and Si to form the quasi p–n junction Gr/Si solar cells, achieving a high power conversion efficiency (PCE) of 10.59% for Gr/Si solar cells without chemical doping. The concept of a self-generated quasi p–n junction offers a possibility to overcome the limitations affecting the development of Gr/Si solar cells, and shows a promising future for diverse transition metal oxides for the fabrication of low-cost, high-efficiency and stable photovoltaic devices in the future.

Design and Photovoltaic Properties of Graphene/Silicon Solar Cell

Graphene/silicon (Gr/Si) Schottky junction solar cells have attracted widespread attention for the fabrication of high-efficiency and low-cost solar cells. However, their performance is still limited by the working principles of Schottky junctions. Modulating the working mechanism of the solar cells into a quasi p–n junction has advantages, including higher open-circuit voltage (VOC) and less carrier recombination. In this study, Gr/Si quasi p–n junction solar cells were formed by inserting a tunneling Al2O3 interlayer in-between graphene and silicon, which led to obtain the PCE up to 8.48% without antireflection or chemical doping techniques. Our findings could pave a new way for the development of Gr/Si solar cells.