Interface and Nanostructural Engineering of Low-cost, Efficient and Stable Perovskite Solar Cells
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Interface and Nanostructural Engineering of Low-cost, Efficient and Stable Perovskite Solar Cells** Zonglong Zhu1 and Shihe Yang1* 1 Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. *corresponding author email: [email protected] ABSTRACT Perovskite solar cells have caught wide attention. High efficiency, low-cost and high stability are among the major goals, which could eventually move the perovskite solar cells to the market. To achieve these goals, interface deliberation and nanostructural engineering hold the key. INTRODUCTION Recently, perovskite typed solar cells (PSCs) based on the organmetal halide perovskite absorber family have attracted great attention in terms of both mesoscopic and planar heterojunctions with their power conversion efficiencies (PCE) reaching over 20%.1 One prominent feature of the perovskites is that the electron-hole diffusion length has reached over 1 Pm in the mixed halide absorber (CH3NH3PbI3-xClx) and 100 nm in the triiodide absorber (CH3NH3PbI3), which much longer than in current low temperature solution-processed photovoltaic materials (typically organic solar cells about 10 nm).2, 3 This, combining with a high open circuit voltage and current density, a broad spectral absorption, etc., has aroused enthusiastic optimism among global researchers to be over the potential of current state of perovskite solar cells.4 The earliest use of perovskite perovskite sensitizer (CH3NH3PbX3, X is halogen) was inspired from the dye-sensitized solar cells, which partnered with the infusion of a liquid electrolyte into a TiO2 mesoporous film, resulting in a 3.8% PV efficiency with lack of stability.5 With boosting development, people replaced the liquid electrolyte by a metal salt doping hole transport layer (HTL) of spiro-OMeTAD, then the cell efficiency was rapidly improved close to 10%.6 The latest power conversion efficiency (PCE) has achieved over 15 % for both mesoporous and planar cell architectures.7, 8 Spiro-OMeTAD suffered from its low mobility in its pristine form although it is as a small molecule hole conductor has been a game changer for the perovskite solar cells. It is well-known that the hole mobility has been improved by over an order of magnitude after doping with cobalt electrolyte and lithium salts together, but it remains an efficiency limiting factor of perovskite solar cells.7 Recently, other small molecule hole transport small molecular have also been publisheded by the derivatives of pyrene and thiophene.9, 10 Meanwhile the conjugated polymers such as the arylamine derived polymers were explored as hole transporting and electron blocking layers.11 The latest efficiency achieved over 18% with PTAA in meso-superstructured perovskite solar cells and over 12% and 10% with poly-TPD and P3HT in planar thin film perovskite solar cells.12, 13 Over the past few years, we have focused on the interface and nanostructural engineering of perovskite solar cells due to their importance from both the fundamental and practical
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