high-work-function contact. For the same reason, electrons are extracted from C60 at the CalMEH-PPV:C,, interface. The result, then, is that separated carriers are not "wasted": thev are automaticallv collected by the prope; electrode so that external work can be done.The substantial enhancement in n ' C achieved with the bicontinuous D-A network material results from the large increase in the interfacial area over that in a D-A bilayer and from the relatively short distance from any point in the polymer to a charge-separating interface. Moreover, the internal D-A junctions inhibit carrier recombination and thereby improve the lifetime of the photoinduced carriers (6), so that the separated charge carriers can be efficiently collected by the built-in field from the asymmetric electrodes. Similar effects have been observed in MEH-PPV:Cyano-PPV polymer blends (10 , 1 1).The device efficiencies are not yet optimized. Because only -60% of the incident power was absorbed at 430 nm in the thinfilm devices used for obtaining the data in u Fig. 3, the internal carrier collection efficiency and energy conversion efficiency are approximately 1.7 times larger; that is, qc.= 90% e/ph and qr;-5.5% at 10 p,W/cm2. Although nearly 100% absorption can be achieved"by using thicker films, qc is currently limited in thick-film devices by internal resistive losses. Further imorovements in device efficiencies are expected when the blend com~ositionand the network morphology are optimized. SCIENCE VOL. 270 15 DECEMBER 1995

Methanolysis of {t-Bu2In[μ-P(SiMe3)2]}2 (1) in aromatic solvents gives polycrystalline InP fibers (dimensions 10−100 nm × 50−1000 nm) at 111−203 °C. The chemical pathway consists of a molecular component, in which precursor substituents are eliminated, and a nonmolecular component, in which the InP crystal lattices are assembled. The two components working in concert comprise the solution−liquid−solid (SLS) mechanism. The molecular component proceeds through a sequence of isolated and fully characterized intermediates:  1 → [t-Bu2In(μ-OMe)]2 (2) → [t-Bu2In(μ-PHSiMe3)]2 (3) → 2 → [t-Bu2In(μ-PH2)]3 (4). Complex 4, which is alternatively prepared from t-Bu3In and PH3, undergoes alkane elimination, the last steps of which are catalyzed by the protic reagent MeOH, PhSH, Et2NH, or PhCO2H. In the subsequent nonmolecular component of the pathway, the resulting (InP) n fragments dissolve into a dispersion of molten In droplets, and recrystallize as the InP fibers. Important criteria are identified for crystal growth of covalent nonmolecular solids from (organic) solution. The outcomes of other solution-phase semiconductor syntheses are rationalized according to the functioning of molecular and nonmolecular pathway components of the kind identified here.

Semiconductor crystal growth at low temperatures and under mild reaction conditions would usher in a technological revolution. Following a brief discussion of the processes that occur during crystal growth, several growth techniques are described, including electrodeposition and surfactant‐interface growth. Particular attention is paid to solution–liquid–solid growth, a technique discovered by the authors that resembles a living polymerization and a phase transfer reaction, by which crystalline III—V materials are produced at the lowest known growth temperatures.

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