The photovoltaics of organic−inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regarding compositional engineering of the hybrid perovskite structure are discussed, including potentials for developing all-inorganic and lead-free perovskite materials. Looking at the latest cutting-edge research, the prospects for perovskite-based photovoltaic and optoelectronic devices, including non-photovoltaic applications such as X-ray detectors and image sensing devices in industrialization, are described. In addition to the aforementioned major topics, we also review, as a background, our encounter with perovskite materials for the first solar cell application, which should inspire young researchers in chemistry and physics to identify and work on challenging interdisciplinary research problems through exchanges between academia and industry. CONTENTS 1. Discovery and Background of Perovskite Photovoltaics 3037 1.1.

Although inorganic perovskite, CsPbI 3 , shows superior thermal stability over organic−inorganic hybrid perovskites, stabilization of the photoactive black phase (α-CsPbI 3 ) of CsPbI 3 perovskite at room temperature and in ambient conditions has remained a challenge. Herein, we present a method of stabilizing the α-CsPbI 3 at lower annealing temperature (85 °C) by incorporation of Eu 3+ (EuCl 3 ) into CsPbI 3 , which prevents the black to the yellow phase (δ-CsPbI 3 ) transformation in ambient air (room temperature) for a reasonably long time (>30 days). Photovoltaic performance of this Eu-stabilized α-CsPbI 3 , as assessed in planar heterojunction solar cells (FTO/TiO 2 /CsPbI 3 :xEu/spiro-OMeTAD/Au), shows a power conversion efficiency above 6% on backward scan (stabilized power output above 4%) for CsPbI 3 :xEu cells with 5−6 mol % of Eu, while CsPbI 3 without Eu, as expected, shows no photovoltaic property at all. However, as the cell stability was found to be affected by composition of organic hole transport material (HTM) (spiro-OMeTAD) and morphology of CsPbI 3 film, it is believed that optimization of cell composition and structure with a more suitable HTM will further improve the cell performance, as well as life.

Undertaken this study to understand the performance degradation of perovskite solar cells at high temperature and under a humid environment, and then tried to reuse the perovskite films from the degraded cells to recover the cell efficiency so as to avoid Pb-waste.

The hole transport material, spiro-OMeTAD, in MAPbI3 perovskite solar cells undergoes severe morphological deformation at high temperature, showing big voids in the layer when the devices are heated at 80 °C and above. It is puzzling that the voids emerge only in the area where the spiro-OMeTAD is capped with Au film and only in the case where the HTM contains both LiTFSI and TBP as additives.

Perovskite solar cells (PSCs) have made incredibly fast progress in past years, pushing the efficiency approaching 26%, which is comparable to the best silicon solar cells. One of the features...