wangzhaowei

Electrically driven reversible structural conversion between the MAPbI₃ and PbI₂ phase in MAPbI₃ at 330 K is first reported, which provides insights into the intrinsic stability and chemical activities of MAPbI₃ materials. Meanwhile, direct visualization of the macro­scopic migration of iodine anions is also reported for the first time, which provides strong evidence for the iodine ions migration.

Highly efficient transparent conductive oxide (TCO)-free perovskite (CH₃NH₃PbI₃) solar cells are demonstrated by using a graphene transparent anode and organic carrier transport materials. By adding a few nanometer-thick MoO₃ layer, wettability and work function of the graphene electrode are enhanced to enable a 17.1% power conversion efficiency, which is so far the highest efficiency for TCO-free solar cells.

The field of organic photovoltaics has recently produced highly efficient single-junction cells with power conversion efficiency >10%, yet the open-circuit voltage (V_OC) remains relatively low in many high performing systems. An accurate picture of the density of states (DOS) in working solar cells is crucial to understanding the sources of voltage loss, but remains difficult to obtain experimentally. Here, the tail of the DOS is characterized in a number of small molecule bulk heterojunction solar cells from the charge density dependence of V_OC, and is directly compared to the disorder present within donor and acceptor components as measured by Kelvin probe. Using these DOS distributions, the total energy loss relative to the charge transfer state energy (E_CT)—ranging from ≈0.5 to 0.7 eV—is divided into contributions from energetic disorder and from charge recombination, and the extent to which these factors limit the V_OC is assessed.

The open-circuit voltage in organic photovoltaic devices is well below the thermodynamic limit due to high rates of bimolecular recombination and energetic disorder. Here, the effect of disorder on voltage loss in molecular bulk heterojunction solar cells is carefully determined from a range of in situ energetic measurements.

Organometal trihalide perovskites have recently emerged as promising materials for low-cost, high-efficiency solar cells. In less than five years, the efficiency of perovskite solar cells (PSC) has been updated rapidly as a result of new strategies adopted in their fabrication process, including device structure, interfacial engineering, chemical compositional tuning, and crystallization kinetics control. To date, the best PSC efficiency has reached 20.1%, which is close to that of single crystal silicon solar cells. However, the stability of PSC devices is still unsatisfactory and is the main bottleneck impeding their commercialization. Here, we summarize recent studies on the degradation mechanisms of organometal trihalide perovskites in PSC devices, and the strategies for stability improvement.

Organometal trihalide solar cells, despite their high efficiency and low cost, still have a serious air instability limitations. Recent studies of the degradation mechanisms of organometal trihalide perovskites in photovoltaics and various strategies for stability improvement are summarized.

Currently, one main challenge in organic solar cells (OSCs) is to achieve both good stability and high power conversion efficiencies (PCEs). Here, highly efficient and long-term stable inverted OSCs are fabricated by combining controllable ZnMgO (ZMO) cathode interfacial materials with a polymer:fullerene bulk-heterojunction. The resulting devices based on the nanocolloid/nanoridge ZMO electron-transporting layers (ETLs) show greatly enhanced performance compared to that of the conventional devices or control devices without ZMO or with ZnO ETLs. The ZMO-based OSCs maintain 84%–93% of their original PCEs over 1-year storage under ambient conditions. An initial PCE of 9.39% is achieved for the best device, and it still retains a high PCE of 8.06% after 1-year storage, which represents a record high value for long-term stable OSCs. The excellent performance is attributed to the enhanced electron transportation/collection, reduced interfacial energy losses, and improved stability of the nanocolloid ZMO ETL. These findings provide a promising way to develop OSCs with high efficiencies and long device lifetime towards practical applications.

High efficiency inverted organic solar cells (OSCs) with long-term stability are fabricated using controllable nanocolloid/nanoridge ZnMgO as electron-transporting layers (ETLs). A greatly improved efficiency of 9.39% is achieved for the OSCs with an optimized ZnMgO ETL. The device retains 8.06% efficiency after 1-year storage, which represents a record high value for long-term stable OSCs.

Interface engineering is critical for achieving efficient solar cells, yet a comprehensive understanding of the interface between a metal electrode and electron transport layer (ETL) is lacking. Here, a significant power conversion efficiency (PCE) improvement of fullerene/perovskite planar heterojunction solar cells from 7.5% to 15.5% is shown by inserting a fulleropyrrolidine interlayer between the silver electrode and ETL. The interface between the metal electrode and ETL is carefully examined using a variety of electrical and surface potential techniques. Electrochemical impedance spectroscopy (EIS) measurements demonstrate that the interlayer enhances recombination resistance, increases electron extraction rate, and prolongs free carrier lifetime. Kelvin probe force microscopy (KPFM) is used to map the surface potential of the metal electrode and it indicates a uniform and continuous work function decrease in the presence of the fulleropyrrolidine interlayer. Additionally, the planar heterojunction fullerene/perovskite solar cells are shown to have good stability under ambient conditions.

Inverted planar heterojunction perovskite solar cells are optimized to achieve a maximum efficiency of 15.5% by inserting fulleropyrrolidine as an interface modification layer. The interface between silver electrode and electron transport layer is carefully examined using a variety of electrical and surface potential techniques. Interface engineering is critical for achieving high-performance perovskite solar cells.

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is less selective for holes in an inverted-architecture organic photovoltaic (OPV) than it is in a conventional-architecture OPV device due to differences between the interfacial-PSS concentration at the top and bottom of the PEDOT:PSS layer. In this work, thin layers of polysulfonic acids are inserted between the poly(3-hexylthiophene) (P3HT):indene-C₆₀ bisadduct (ICBA) bulk heterojunction (BHJ) active layer and PEDOT:PSS to create a higher concentration of acid at this interface and, therefore, mimic the distribution of materials present in a conventional device. Upon thermal annealing, this acid layer oxidizes P3HT, creating a thin p-type interlayer of P3HT⁺/acid⁻ on top of the BHJ. Using X-ray absorption spectroscopy, Kelvin probe, and ellipsometry measurements, this P3HT⁺/acid⁻ layer is shown to be insoluble in water, indicating it remains intact during the subsequent deposition of PEDOT:PSS. Current density–voltage measurements show this doped interlayer reduces injected dark current while increasing both open-circuit voltage and fill factor through the creation of a more hole selective BHJ-PEDOT:PSS interface.

Thin layers of sulfonic acid polymers are used to create a doped interlayer in organic photovoltaic devices. The presence of a p-type doped interlayer between the bulk heterojunction (BHJ) and the PEDOT:PSS hole transport layer (HTL) increases the hole selectivity of the BHJ-HTL interface, which increases the open-circuit voltage and fill factor.

Highly transparent electrodes with a well-tuned refractive index are essential for a wide range of optoelectronic devices, such as light emitting diodes and solar cells. Here, it is shown that the transparency of ZnO:Al can be improved and its refractive index can be reduced simultaneously by the addition of SiO₂ into the layer. It is found that for low SiO₂ concentrations, Si quenches oxygen vacancies and improves the layer transparency. At higher SiO₂ concentrations a highly transparent amorphous compound of Zn_xSi_yO:Al forms, with a refractive index that scales down with the relative Si/Zn ratio. These layers are tested in Si heterojunction solar cells by inserting them between Si and the metallic rear contact of such devices. A consistent improvement is found in the cell short-circuit current density and external quantum efficiency with increasing Si incorporation. Our findings establish a general strategy to tune the optical properties of transparent conductive oxides for improved light management in solar cells.

Transparent conductive oxides with tunable refractive index and optical transparency are obtained by adding the highly transparent and low-refractive SiO₂ to ZnO:Al. Si has different functions in ZnO:Al depending on its concentration. A ZnO:Al layer with an optimized SiO₂ concentration significantly improves the infrared external quantum efficiency of a c-Si heterojunction solar cell.

In article number 1501406, Dae-Eun Kim, Min Jae Ko, and co-workers report highly efficient and ITO-free ultra-flexible perovskite solar cells on a shape recovery polymer substrate. The solar cell shows not only outstanding and consistent photovoltaic performance, but also complete shape recovery, even after undergoing repeated bending at an extremely low radius (1 mm) without significant mechanical damage. This provides a potential application to stretchable and wearable energy power supply devices.