The thin-fi lm photovoltaic material Cu 2 ZnSnS x Se 4-x (CZTSSe) has drawn world-wide attention due to its outstanding performance and earth-abundant composition. Until recently, [ 1 ] stateof-the-art CZTSSe thin-fi lm solar cells were limited to 11.1% power conversion effi ciency (PCE), with these performance levels being achieved via a hydrazine slurry approach. [ 2 ] Other vacuum-and non-vacuum-based deposition techniques have also been successful in fabricating CZTSSe solar cells with PCE above 8%. [ 3,4 ] However, even record devices with PCE of 11% are still far below the physical limit, known as the ShockleyQueisser (SQ) limit, of about 31% effi ciency under terrestrial conditions. [ 5 ] For a solar cell with 1.13 eV bandgap such as the previous 11.1% champion, [ 2 ] the SQ limits for open circuit voltage ( V oc ) and short-circuit current density ( J sc ) are 820 mV and 43.4 mA cm −2 , respectively. The previous 11.1% champion only achieved a V oc of 460 mV and a J sc of 34.5 mA cm −2 , corresponding to about 56% and 79% of the SQ limit values. In order to boost J sc , an optical architecture with optimized transparent conductive oxide (TCO) and CdS thicknesses has recently been reported, leading to a new CZTSSe record PCE of 12.0% and a J sc that reaches 83% of the SQ limit. [ 1 ] Despite improvements in shortcircuit current, the V oc defi cit, equal to the difference between the bandgap and V oc , is currently the biggest hurdle preventing CZTSSe devices from achieving higher effi ciency. [ 6 ] Enhancement of V oc also directly improves device fi ll factor. [ 7 ] Although many factors can infl uence V oc in a solar cell, carrier generation and recombination near the charge-separating junction play a dominant role. Thus, in order to decrease the V oc defi cit and increase effi ciency beyond 12%, it is critical to understand junction characteristics, current collection, and recombination mechanisms in the current generation of devices.Here, an independently certifi ed world-record 12.6% PCE CZTSSe thin-fi lm solar cell is presented. The new champion device was fabricated using a recently described hydrazine pure-solution approach, targeting a Cu-poor and Zn-rich condition. [ 8 ] Secondary ion mass spectrometry (SIMS) shows that the obtained CZTSSe fi lms exhibit very low carbon and oxygen concentrations, comparable to fi lms fabricated by the more traditional hydrazine-slurry method. [ 9 ] The rheological properties of the particle-free solution, relative to the slurry process, signifi cantly improves the coating uniformity and fi lm structure and, consequently, the performance of the solar cells. [ 4,8 ] By simultaneously optimizing the TCO and CdS thicknesses to maximize photon transmission to the absorber and improving the bulk qualities of CZTSSe with the hydrazine pure-solution approach, both J sc and V oc are boosted in the 12.6% champion device. Device characteristics of the new champion cell, as deduced from current-voltage, quantum effi ciency, capacitance, and electron-beam-induced current (EBI...

Room-temperature infrared sub-band gap photoresponse in silicon is of interest for telecommunications, imaging and solid-state energy conversion. Attempts to induce infrared response in silicon largely centred on combining the modification of its electronic structure via controlled defect formation (for example, vacancies and dislocations) with waveguide coupling, or integration with foreign materials. Impurity-mediated sub-band gap photoresponse in silicon is an alternative to these methods but it has only been studied at low temperature. Here we demonstrate impurity-mediated room-temperature sub-band gap photoresponse in single-crystal silicon-based planar photodiodes. A rapid and repeatable laser-based hyperdoping method incorporates supersaturated gold dopant concentrations on the order of 10 20 cm À 3 into a single-crystal surface layer B150 nm thin. We demonstrate room-temperature silicon spectral response extending to wavelengths as long as 2,200 nm, with response increasing monotonically with supersaturated gold dopant concentration. This hyperdoping approach offers a possible path to tunable, broadband infrared imaging using silicon at room temperature.

Integrating a silicon solar cell with a recently developed cobaltbased water-splitting catalyst (Co-Pi) yields a robust, monolithic, photo-assisted anode for the solar fuels process of water splitting to O 2 at neutral pH. Deposition of the Co-Pi catalyst on the Indium Tin Oxide (ITO)-passivated p-side of a np-Si junction enables the majority of the voltage generated by the solar cell to be utilized for driving the water-splitting reaction. Operation under neutral pH conditions fosters enhanced stability of the anode as compared to operation under alkaline conditions (pH 14) for which long-term stability is much more problematic. This demonstration of a simple, robust construct for photo-assisted water splitting is an important step towards the development of inexpensive direct solar-to-fuel energy conversion technologies.photoelectrochemical | hydrogen | solar energy | storage P hotosynthetic organisms convert the energy of sunlight into chemical energy by splitting water, producing molecular oxygen and hydrogen equivalents in the highly conserved enzyme complex photosystem II (PSII) (1). Absorbed photons are transferred to the reaction center of PSII, where a single electron/hole charge separation occurs. The oxidative power of the photo-produced hole in PSII is transferred to the oxygen evolving complex (OEC) where water splitting occurs. The electron is transferred to the adjacent photosystem I (PSI), where it participates in the reduction reaction of NAD þ into NADH, which is ultimately used to fix CO 2 . Crucial in the above configuration is the separation of the functions of light collection and conversion from catalysis. Whereas light collection/conversion generates electron/ hole pairs one at a time, water splitting is a four-electron/hole process (2, 3). Hence, the multielectron catalysts of PSII and PSI, positioned at the terminus of the photosynthetic charge-separating network, are compulsory so that the one photon-one-electron/ hole "wireless current" can be bridged to the four-electron/hole chemistry of water splitting.An artificial photosynthesis can be designed if the one-electron/hole wireless current of a semiconductor can be integrated directly with catalysts to perform the four-electron-four proton catalysis of water splitting. To this end, an important recent advance has been the creation of a cobalt-phosphate (Co-Pi) catalyst (4, 5) that captures the functional elements of the OEC of PSII (6). As in PSII OEC, the Co-Pi catalyst self-assembles upon oxidation of an earth-abundant metal [Co 2þ for Co-Pi vs. Mn 2þ for OEC (7-9)] in phosphate-buffered solutions at neutral pH (4, 10), exhibits high activity in natural water and sea water at room temperature (11), activates water by proton-coupled electron transfer (3) [as does the OEC of PSII (12, 13)], and is self-healing (14) [as is PSII (15-18)]. Moreover, X-ray Absorption Spectroscopy (XAS) studies (19,20) have established that the Co-Pi catalyst is a structural relative of PSII OEC. PSII OEC is a Mn 3 CaO 4 -Mn cubane (21) where the fourth M...

We observe an insulator-to-metal (I-M) transition in crystalline silicon doped with sulfur to nonequilibrium concentrations using ion implantation followed by pulsed laser melting and rapid resolidification. This I-M transition is due to a dopant known to produce only deep levels at