For highly interested organolead perovskite based solar cells, the exciton and free carriers are the photoproducts in the working layers. In this study, we revealed their two forms of relations depending on heat-annealing condition. In non-annealed films and single crystal, they are in density-dependent dynamical balance (co-existing). For the sufficiently heat-annealed films, they present a significant emissive exciton-carrier collision (ECC). The two relations indicate the emergence of a subgrain morphology within the tetragonal phase of crystal grain, induced by heat annealing process. Such subgrain structure could be assigned to a ferroelastic twinning structure recently found inside the crystal grain of the films. Since the heat annealing is a general procedure in preparing perovskite working layers, we propose that the ECC and subgrain morphology widely exist in real devices. We suggest that the subgrain structure provides another level of morphological basis for in depth understanding high performance of organolead perovskite working layers.

Recently, perovskite solar cells have attracted tremendous research interest due to their amazing light to electric power conversion efficiency (PCE). However, most high performance devices usually use mesoporous TiO2 as the electron transport layer (ETL), which increases cost for practical application. Here, TiO2/SnOxCly double layer was employed as the ETL for planar perovskite solar cells. Compared with bare TiO2, perovskite solar cell based on TiO2/SnOxCly shows drastically improved power conversion efficiency and reduced hysteresis. These improvements are attributed to TiO2/SnOxCly which could enhance electron extraction and reduce surface trap-state. (C) 2017 Elsevier B.V. All rights reserved.

Poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) is one of the most widely used hole transport layers (HTL) in inverted perovskite solar cells (PSCs) due to its simple solution-processed ability, high transparency, and conductivity. However, PEDOT: PSS-based devices suffer a lower open-circuit voltage (V-oc) than devices with the conventional structure. To address this issue, we fabricated ammonia-modified PEDOT: PSS films by simply doping PEDOT: PSS solution with different ratio of ammonia. The acidity of PEDOT: PSS can be neutralized by the doped ammonia, which inhibits the ion-exchange reaction between PSS-H and CH3NH3I, thus retarding the reduction of the work function for PEDOT: PSS to some extent. As a result, a superior power conversion efficiency (PCE) of 15.5% was obtained for the device based on the ammonia-doped PEDOT: PSS HTL than that of the pristine PEDOT: PSS-based device. We ascribe the PCE enhancement to the increased Voc and fill factor (FF), which is attributed not only to the better energy-level alignment between the ammonia-modified PEDOT: PSS film and perovskite layer but also to the increased grain size and crystallinity of perovskite film. (C) 2017 Published by Elsevier B.V.

In recent years, perovskite solar cells have drawn a widespread attention. As an electrode material, fluorine-doped tin oxide (FTO) is widely used in various kinds of solar cells. However, the relatively low work function (WF) (similar to 4.6 eV) limits its application. The potential barrier between the transparent conductive oxide electrode and the hole transport layer (HTL) in inverted perovskite solar cells results in a decrease in device performance. In this paper, we propose a method to adjust WF of FTO by implanting zirconium ions into the FTO surface. The WF of FTO can be precisely and continuously tuned between 4.59 and 5.55 eV through different dopant concentration of zirconium. In the meantime, the modified FTO, which had a WF of 5.1 eV to match well the highest occupied molecular orbital energy level of poly(3,4-ethylenedioxylenethiophene):polystyrene sulfonate, was used as the HTL in inverted planar perovskite solar cells. Compared with the pristine FTO electrode-based device, the open circuit voltage increased from 0.82 to 0.91 V, and the power conversion efficiency increased from 11.6 to 14.0%.

High-efficiency organic inorganic hybrid perovskite solar cells have experienced rapid development and attracted significant attention in recent years. Crystal growth as an important factor would significantly influence the quality of perovskite films and ultimately the device performance, which usually requires thermal annealing for 10 min or more. Herein, we demonstrate a new method to get high crystallization of perovskite film by electric current annealing for just 5 s. In contrast to conventional thermal annealing, a homogeneous perovskite film was formed with larger grains and fewer pinholes, leading to a better performance of the device with higher open-circtlit voltage and fill factor. An average power conversion efficiency of 17.02% with electric current annealing was obtained, which is higher than that of devices with a conventional thermal annealing process (16.05%). This facile electric current annealing process with legs energy loss and time consumption shows great potential in the industrial mass production of photovoltaic devices.

Interfacial materials play a critical role in photoelectric conversion properties as well as the anomalous hysteresis phenomenon of the perovskite solar tells (PSCs), In this article, a water-soluble polythiophene PTEBS was employed as a cathode interfacial, material for PSCs. Efficient energy level aligning and improved film morphology Were obtained due to an ultrathin coating of PTEBS. Better ohmic contact :between the perovskite layer and the cathode also benefits the charge transport and extraction of the device. Moreover, less charge accumulation at the interface weakens the polarization of the perovskite resulting in a relatively quick response of the modified device. The ITO/PTEBS/CH3NH3PbI3/spiro-MeOTAD/Au cells by an all low-temperature process achieved power conversion efficiencies of up to 15.4% without apparent hysteresis effect. Consequently, the utilization of this water-soluble polythiophene is a practical approach for the fabrication of highly efficient, large-area, and low-cost PSCs and compatible with low:temperature solution process, roll-to-roll manufacture, and flexible application.

The past five years have witnessed the significant breakthrough of perovskite solar cells (PSCs). High certificated power conversion efficiency (PCE) of 22.1% was achieved in a short time after the inorganic-organic perovskite was firstly used as the light absorber in the solar cells. It is believed that PSCs now become one of the most promising photovoltaic in the new-generation solar cells, which may rival silicon based solar cells. In this article, simplified planar perovskite solar cells without a hole-blocking layer were fabricated by a two-step spin-coating method, and the highest PCE of 15.1% was achieved with an average PCE of 13.6%. Moreover, it is found that the hysteresis effect is reduced in this kind of devices. The research on improved performance for the PSCs with simplified device architecture is very important both for understanding the working mechanism of cells, and for fabricating low-cost and high-performance PSCs to approach commercial applications. (C) 2017 Published by Elsevier Ltd.

Inverted planar heterojunction perovskite solar cells with poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) sulfonic acid (PEDOT:PSS) as the hole transport layer (HTL) have attracted significant attention during recent years. However, these devices suffer from a serious stability issue due to the acidic and hygroscopic characteristics of PEDOT: PSS. In this work, we demonstrate a room-temperature and solution-processed CuI film which is used as the HTL for inverted perovskite solar cells. As a result, an impressive PCE of 16.8% is achieved by the device based on the CuI HTL. Moreover, the unsealed CuI-based device displays enhanced air stability compared to the PEDOT: PSS-based device. In addition, the fabrication of the CuI HTL is a simple and time-saving procedure without any post-treatment, thus making it a promising candidate as the HTL in inverted perovskite solar cells and a potential target for efficient flexible and tandem solar cells.

The high efficiency of perovskite solar cells benefits from the high density of photoinduced free carriers. We studied how exciton and free carriers, as the two major photoproducts, coexist inside the CH3NH3PbI3 perovskite. A new density-resolved spectroscopic method was developed for this purpose. The density-dependent coexistence of excitons and free carriers over a wide density range was experimentally observed. The quantitative analysis on the density-resolved spectra revealed a moderate exciton binding energy of 24 +/- 2 meV. The results effectively proved that the strong ionic polarization inside the perovskite has a negligible contribution to exciton formation. The spectra also efficiently uncovered the effective mass of electron-hole pairs. Our spectroscopic method and the results profoundly enrich the understanding of the photophysics in perovskite materials for photovoltaic applications.

Ferroelectric materials exhibiting anomalous photovoltaic properties are one of the foci of photovoltaic research. We review the foundations and recent progress in ferroelectric materials for photovoltaic applications, including the physics of ferroelectricity, nature of ferroelectric thin films, characteristics and underlying mechanism of the ferroelectric photovoltaic effect, solar cells based on ferroelectric materials, and other related topics. These findings have important implications for improving the efficiency of photovoltaic cells.