Longevity has been a long-standing concern for hybrid perovskite photovoltaics. We demonstrate high-resilience positive-intrinsic-negative perovskite solar cells by incorporating a piperidinium-based ionic compound into the formamidinium-cesium lead-trihalide perovskite absorber. With the bandgap tuned to be well suited for perovskite-on-silicon tandem cells, this piperidinium additive enhances the open-circuit voltage and cell efficiency. This additive also retards compositional segregation into impurity phases and pinhole formation in the perovskite absorber layer during aggressive aging. Under full-spectrum simulated sunlight in ambient atmosphere, our unencapsulated and encapsulated cells retain 80 and 95% of their peak and post-burn-in efficiencies for 1010 and 1200 hours at 60° and 85°C, respectively. Our analysis reveals detailed degradation routes that contribute to the failure of aged cells.
The short exciton diffusion length associated with most classical organic semiconductors used in organic photovoltaics (5-20 nm) imposes severe limits on the maximum size of the donor and acceptor domains within the photoactive layer of the cell. Identifying materials that are able to transport excitons over longer distances can help advancing our understanding and lead to solar cells with higher efficiency. Here, we measure the exciton diffusion length in a wide range of nonfullerene acceptor molecules using two different experimental techniques based on photocurrent and ultrafast spectroscopy measurements. The acceptors exhibit balanced ambipolar charge transport and surprisingly long exciton diffusion lengths in the range of 20 to 47 nm. With the aid of quantum-chemical calculations, we are able to rationalize the exciton dynamics and draw basic chemical design rules, particularly on the importance of the end-group substituent on the crystal packing of nonfullerene acceptors.
High mobility thin‐film transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thin‐film transistors is reported that exploits the enhanced electron transport properties of low‐dimensional polycrystalline heterojunctions and quasi‐superlattices (QSLs) consisting of alternating layers of In2O3, Ga2O3, and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180–200 °C). Optimized prototype QSL transistors exhibit band‐like transport with electron mobilities approximately a tenfold greater (25–45 cm2 V−1 s−1) than single oxide devices (typically 2–5 cm2 V−1 s−1). Based on temperature‐dependent electron transport and capacitance‐voltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gas‐like systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, roll‐to‐roll, etc.) and can be seen as an extremely promising technology for application in next‐generation large area optoelectronics such as ultrahigh definition optical displays and large‐area microelectronics where high performance is a key requirement.
We report the synthesis of a selenophene -diketopyrrolopyrrole monomer and its co-polymerisation with selenophene and thieno [3,2-b]thiophene monomers by Stille coupling. The resulting low band gap polymers exhibit ambipolar charge transport in organic field effect transistors. High and balanced electron and hole mobilities in excess of 0.1 cm 2 V -1 s -1 were observed in bottom gate, bottom contact devices, 10 suggesting that selenophene inclusion is a promising strategy for the development of ambipolar organic semiconductors.
ABSTRACT:While recent improvements in the reported peak power conversion efficiency (PCE) of hybrid organic-inorganic perovskite solar cells have been truly astonishing, there are many fundamental questions about the electronic behavior of these materials. Here we have studied a set of electronic devices employing methylammonium lead iodide ((MA)PbI 3 ) as the active material and conducted a series of temperature-dependent measurements. Field-effect transistor, capacitor and photovoltaic cell measurements all reveal behavior consistent with substantial and strongly temperature-dependent polarization susceptibility in (MA)PbI 3 at temporal and spatial scales that significantly impact functional behavior. The relative PCE of (MA)PbI 3 photovoltaic cells is observed to reduce drastically with decreasing temperature, suggesting that such polarization effects could be a prerequisite for high-performance device operation. The pace at which new materials and designs for solar cells emerge is very slow, [1][2][3][4][5][6] and is arguably comparable to the discovery of high T c superconductors. [7][8] The finding that hybrid organic metal halide solar cells based on CH 3 NH 3 PbI 3 can lead to high power conversion efficiency (PCE) using simple coating methods, in a material comprising earth-abundant elements has therefore garnered significant interest. 6, 9-10 Not only has the peak reported PCE exceeded 20% in a short time, [11][12][13] but the processing techniques widely employed suggest that commercial products could be fabricated using low-cost, large-area techniques, potentially compatible with flexible substrates.
14The ABX 3 perovskite crystal structure is characterized by three-dimensionally corner connected network of BX 6/2 octahedra that is filled by the A ions. Perovskite compounds where the A is an organic cation, B is usually a main group element, and X is a group 7 anion (halide) We found that the electrical characteristics of (MA)PbI 3 had a complex temperature dependence. At room temperature these devices exhibit low source-drain currents and no fieldinduced current modulation (see Figure 1(a)). However when the temperature is reduced below 220K, a field-effect is observed and the drain current continues to increase as the temperature is reduced. Where the drain current is observed to be substantially in excess of gate current the gradual-channel approximation 44 has been applied to extract a value of field-effect mobility. The gradual channel approximation for extraction of carrier mobility in field-effect devices assumes a single electronic charge carrier, uniform carrier accumulation in the channel, and timeindependent behavior and consequently does not provide a simple estimation of the carrier motion for measurements with non-ideal effects. This is consistent with our observation of absolute values of electron mobility substantially lower than those previously reported using other techniques. 16 Nonetheless it can be applied as a proxy for relative transistor performance, assuming a high transcondu...
Solution-processable organic metal halide Ruddlesden− Popper phases have shown promise in optoelectronics because of their efficiencies in solar cells along with increased material stability relative to their three-dimensional counterparts (CH 3 NH 3 PbI 3 ). Here, we study the layered material butylammonium methylammonium lead iodide (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) n−1 Pb n I 3n+1 for values of n ranging from 1 to 4. Thin films cast from solution show a gradual change in the crystalline texture of the two-dimensional lead iodide layers from being parallel to the substrate to perpendicular with increasing n. Contactless timeresolved microwave conductivity measurements show that the average recombination rate order increases with n and that the yield−mobility products and carrier lifetimes of these thin films are much lower than that of CH 3 NH 3 PbI 3 , along with increased higher-order recombination rate constants.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.