Cross-sections of a hole-conductor-free CH3NH3PbI3 perovskite solar cell were characterized with Kelvin probe force microscopy. A depletion region width of about 45 nm was determined from the measured potential profiles at the interface between CH3NH3PbI3 and nanocrystalline TiO2, whereas a negligible depletion was measured at the CH3NH3PbI3/Al2O3 interface. A complete solar cell can be realized with the CH3NH3PbI3 that functions both as light harvester and hole conductor in combination with a metal oxide. The band diagrams were estimated from the measured potential profile at the interfaces, and are critical findings for a better understanding and further improvement of perovskite based solar cells.
High voltage hole conductor free perovskite solar cell achieved 1.35 V.
This work demonstrates antisolvent treatment of organo-metal halide perovskite film in hole-conductor-free perovskite-based solar cell, achieving impressive power conversion efficiency of 11.2% for hole-conductor-free cells with gold contact. We found that antisolvent (toluene) surface treatment affects the morphology of the perovskite layer, and importantly, it also affects the electronic properties of the perovskite. Conductive atomic force microscopy (cAFM) and surface photovoltage show that the perovskite film becomes more conductive after antisolvent treatment. Moreover, the antisolvent treatment suppresses the hysteresis commonly obtained for perovskite-based solar cells. When the perovskite alone is characterized, a I−V plot of a single perovskite grain measured by cAFM shows that hysteresis vanishes after toluene treatment. During toluene treatment, excess halide and methylammonium ions are removed from the perovskite surface, leading to a net positive charge on the Pb atoms, resulting in a more conductive perovskite surface, which is beneficial for the hole-conductor-free solar cell structure. The reliability of the surface treatment was proved by calculating the statistical parameters Z score and p value, which were 2.5 and 0.012, respectively. According to these values, it can be concluded with 95% confidence that the average efficiency of cells fabricated via surface treatment is greater than the average efficiency of cells without surface treatment. The statistical data support the impact of surface treatment on the photovoltaic performance of perovskite solar cells.
In this work we demonstrate the planar configuration on hole conductor (HTM) free perovskite based solar cells. The CH 3 NH 3 PbI 3 perovskite was deposited using the spray technique to achieve micrometer size perovskite crystals. The number of spray passes changes the CH 3 NH 3 PbI 3 film thickness; for example, 10 spray passes achieved a film thickness of 3.4 μm of perovskite. Surprisingly, power conversion efficiency of 6.9% was demonstrated for this novel, simple solar cell structure with thick perovskite film that has no HTM. Capacitance−voltage measurements reveal charge accumulation at the CH 3 NH 3 PbI 3 /Au interface while the compact TiO 2 /CH 3 NH 3 PbI 3 junction showed a space charge region, which inhibits the recombination. Studying these interfaces is key to understanding the operation mechanism of this unique solar cell structure. This simple planar HTM free perovskite solar cell demonstrates the potential to make large-scale solar cells while maintaining a simple, low-cost architecture. ■ INTRODUCTIONOrganometal perovskite is a hybrid material composed of inorganic and organic components having high absorption coefficient, direct band gap, and high carrier mobility, 1−3 making it attractive for photovoltaic (PV) solar cells. In recent years, organometal perovskite has been used intensively in PV solar cells, achieving a power conversion of 20.1%. 4 Long electron−hole diffusion length was demonstrated in organometal perovskite which contributes to the high power conversion efficiency. 5,6 The perovskite based solar cells are not restricted to a specific solar cell configuration as might occur in other solar cell technologies. It has been demonstrated that perovskite, with and without the ability to inject electrons, functions on mesoporous metal oxide. 7−9 The perovskite can also be used both as a hole conductor (HTM) and as a light harvester due to the efficient hole and electron mobility, making the solar cell structure even simpler. HTM free cells show PV performance of 10−12% efficiency. 10−15 In addition, it is possible to observe efficient perovskite solar cells in planar architecture. In this solar cell structure, the perovskite is usually deposited on a planar substrate, contrary to the mesoporous configuration. One of the first reports on planar architecture discussed the evaporation of the organometal perovskite, achieving a uniform perovskite film with more than 15% efficiency. 16 Moreover, a vapor-assisted solution process was demonstrated as an efficient deposition technique for the planar structure, achieving 12.1% efficiency. 17 Flexible, low temperature planar perovskite solar cells were demonstrated on ZnO nanoparticles exceeding 10% efficiency 18 and on polymer substrate in an inverted configuration, where the perovskite was deposited between PDOT:PSS and PCBM. 19 Recently, inverted planar perovskite based solar cells where a CuSCN layer was deposited on the ITO surface showed 15.6% efficiency. The low interface contact resistance between the perovskite, the CuSCN, and the C60 ...
Hybrid organic-inorganic perovskite has proved to be a superior material for photovoltaic solar cells. In this work we investigate the parameters influencing the growth of ZnO nanowires (NWs) for use as an efficient low temperature photoanode in perovskite-based solar cells. The structure of the solar cell is FTO (SnO2:F)-glass (or PET-ITO (In2O3·(SnO2) (ITO)) on, polyethylene terephthalate (PET)/ZnAc seed layer/ZnO NWs/CH3NH3PbI3/Spiro-OMeTAD/Au. The influence of the growth rate and the diameter of the ZnO NWs on the photovoltaic performance were carefully studied. The ZnO NWs perovskite-based solar cell demonstrates impressive power conversion efficiency of 9.06% on a rigid substrate with current density over 21 mA/cm2. In addition, we successfully fabricated flexible perovskite solar cells while maintaining all fabrication processes at low temperature, achieving power conversion efficiency of 6.4% with excellent stability for over 75 bending cycles.
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