Hole-transport-material-free Perovskite Solar Cells Based On Nanoporous Gold Film

Organic inorganic hybrid perovskite CH3NH3PbI3/CH3NH3PbBr3 was first introduced to solar cells in 2009. The power conversion efficiency of perovskite solar cells has developed to 22.1%. The rapid development of perovskite solar cell is benefited by the intrinsic physical properties of CH3NH3PbI3, such as direct band gap semiconductor with a band gap of 1.5eV, broad spectral absorption range from300nm to 800nm, large absorption coefficient, ambipolar charge transport, high carrier mobility, long carrier diffuse length and so on. The research of perovskite solar cells is one of the hot spots in new photovoltaic materials, physics and devices in recent years.Most of the highly efficient perovskite solar cells contain expensive hole transport material (HTM), such as spiro-MeOTAD, P3HT, which will increase fabrication costs. Simultaneously, the using of HTM will make the device structure complex and reduces the stability of the device. HTM-free perovskite solar cell can solve these problems better. For HTM-free perovskite solar cells, holes were transport from CH3NH3PbI3 to back electrode directly. Thus the back electrode of HTM-free perovskite solar cells must not only contains a highly conductivity but also a matched work function to the value band of CH3NH3PbI3. Gold and carbon were the commonly used materials which meet these requirements. Although carbon is a good choice for back electrode, but the conductivity is lower than gold, thus the devices should contains a thick electrode, which is not benefit for the integration of the devices.In this work, nanoporous gold film was used as back electrode for HTM-free perovskite solar cell. We design a special device structure which has no demand for a high quality perovskite film. The CH3NH3PbI3 was infiltrated into the porous of mesoporous layer and nanoporous gold film. Three ways, namely one-step spin-coating deposition, sequential deposition, and two-step spin-coating deposition were introduced to fabricate CH3NH3PbI3. The infiltration and crystallization of CH3NH3PbI3 fabricated by different ways on the performance of the devices was investigated. The infiltration of CH3NH3PbI3 into the porous structure is a critical factor for the device. The devices fabricated by two step spin-coating deposition show best infiltration. The well infiltrated device show the highest power conversion efficiency of 7.99%. We have also investigated the influence of mesoporous Al2O3 on the performance of the devices and the J-V hysteresis of the devices. Our research put forward a new electrode material which can be used in HTM-free perovskite solar cells.