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For efficient hybrid solar cells based on organometal halide perovskites, the real origin of the IV hysteresis became a big issue and has been discussed widely. In this study, simulated IV curves of different equivalent circuit models were validated with experimental IV curves of a planar perovskite solar cell with the power conversion efficiency (PCE) of 18.0% and 8.8% on reverse scan (from open circuit to short circuit) and forward scan (from short circuit to open circuit), respectively. We found that an equivalent circuit model with a series of double diodes, capacitors, shunt resistances, and single series resistance produces simulated IV curves with large hysteresis matching with the experimentally observed curves. The electrical capacitances generated by defects due to the lattice mismatch at the TiO 2 /CH 3 NH 3 PbI 3 and CH 3 NH 3 PbI 3 /spiro-OMeTAD interface are truly responsible for the hysteresis in perovskite solar cells.Perovskite solar cells based on CH 3 NH 3 PbI 3 have attracted enormous attention in the last few years due to their outstanding performance as photovoltaics. The power conversion efficiency (PCE) of the devices has dramatically improved to over 20% in a relatively short duration.1,2 Despite the unique properties and higher efficiencies, several important issues, e.g., mysterious hysteresis in IV curves and durability of stabilized performance, still remained for commercialization.3,4 It has been found the hysteresis strongly depends on the device architecture, where the planar structure and Al 2 O 3 mesoscopic perovskite cells show relatively large hysteresis than TiO 2 mesoporous structure devices. 5 The typical planar structure of SnO 2 :F(FTO)/compact TiO 2 /CH 3 NH 3 PbI 3 /spiro-OMeTAD/Au 6 suffers from severe hysteresis in the IV measurement.3,4 The reverse scan (from the open circuit to the short circuit) always shows higher PCE than the forward scan (from short circuit to the open circuit). Hence, such hysteresis in the IV curves creates ambiguity about the actual performance of the device, which is being suspected to be over-estimated. 7,8 The origin of hysteresis has been discussed on the intrinsic proprieties like ferroelectric polarization 9 and/or ionic migration 10 of the perovskite to date. However, there was no direct evidence that could support the above claims. It has been reported that passivation of TiO 2 layer by C60 or use of phenyl-C61-butyric acid methyl ester (PCBM) instead of TiO 2 in inverted device structure reduces the hysteresis. 1113 The passivation could minimize the trap states and improve electron transfer through the interface of TiO 2 /CH 3 NH 3 PbI 3 , resulting in the reduction of hysteresis.11 On the other hand, PCBM in the inverted cell could extract the carriers (electrons) more efficiently than TiO 2 without accumulation at the interface, and the hysteresis was eliminated. In another standpoint, lattice mismatch of the interfaces containing organic compounds could be ignored and consequently the hysteresis was reduced. The importance of la...

Avoiding cryogenic cooling not only reduces the cost and weight but also simplifies the infrared detector system allowing widespread usage. Here an uncooled infrared detection using intravalence bands is reported. A set of three p-GaAs/ Al x Ga 1−x As multiple heterojunction detector structures were used to demonstrate the concept experimentally. A preliminary detector showed peak responsivity of 0.29 mA/ W at 2.5 m at 300 K. The intravalence band approach can be used to cover various wavelength ranges by using different material systems giving rise to the possibilities of a dual band detector operating in atmospheric windows.

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Energy harvesting at low light intensities has recently attracted a great deal of attention of perovskite solar cells (PSCs) which are regarded as promising candidate for indoor application. Anomalous hysteresis of the PSCs a complex issue for reliable evaluation of the cell performance. In order to address these challenges, we constructed two new evaluation methods to determinate the power conversion efficiencies (PCEs) of PSCs. The first setup is a solar simulator based on light emitting diodes (LEDs) allowing evaluation of the solar cells at wider range of light intensities, ranging from 102 to 10−3 mW·cm−2. As the overestimate error, we found that the PCEs of dye sensitized solar cell (DSC) and PSCs increase dramatically at low light intensities conditions. Due to the internal capacitance at the interfaces on hybrid solar cells, the measurement of current below 10−2 mW·cm−2 shows constant value given high PCE, which is related to the capacitive current and origin of the hysteresis. The second setup is a photovoltaic power analyzing system, designed for tracking the maximum power (P max) with time. The paper suggests the combination of the LED solar simulator and P max tracking technique as a standard to evaluate the PCE of capacitive solar cells.