Global transition path search for dislocation formation in Ge on Si(001)

Global optimization of transition paths in complex atomic scale systems is addressed in the context of misfit dislocation formation in a strained Ge film on Si(001). Such paths contain multiple intermediate minima connected by minimum energy paths on the energy surface emerging from the atomic interactions in the system. The challenge is to find which intermediate states to include and to construct a path going through these intermediates in such a way that the overall activation energy for the transition is minimal. In the numerical approach presented here, intermediate minima are constructed by heredity transformations of known minimum energy structures and by identifying local minima in minimum energy paths calculated using a modified version of the nudged elastic band method. Several mechanisms for the formation of a 90{\deg} misfit dislocation at the Ge-Si interface are identified when this method is used to construct transition paths connecting a homogeneously strained Ge film and a film containing a misfit dislocation. One of these mechanisms which has not been reported in the literature is detailed. The activation energy for this path is calculated to be 26% smaller than the activation energy for half loop formation of a full, isolated 60{\deg} dislocation. An extension of the common neighbor analysis method involving characterization of the geometrical arrangement of second nearest neighbors is used to identify and visualize the dislocations and stacking faults

Monolithic Perovskite Silicon Tandem Solar Cells Fabricated Using Industrial p Type Polycrystalline Silicon on Oxide Passivated Emitter and Rear Cell Silicon Bottom Cell Technology

Combining a perovskite top cell with a conventional passivated emitter and rear cell PERC silicon bottom cell in a monolithically integrated tandem device is an economically attractive solution to boost the power conversion efficiency PCE of silicon single junction technology. Proof of concept perovskite silicon tandem solar cells using high temperature stable bottom cells featuring a polycrystalline silicon on oxide POLO front junction and a PERC type passivated rear side with local aluminum p contacts are reported. For this PERC POLO cell, a process flow that is compatible with industrial, mainstream PERC technology is implemented. Top and bottom cells are connected via a tin doped indium oxide recombination layer. The recombination layer formation on the POLO front junction of the bottom cell is optimized by postdeposition annealing and mitigation of sputter damage. The perovskite top cell is monolithically integrated in a p amp; 8722;i amp; 8722;n junction device architecture. Proof of concept tandem cells demonstrate a PCE of up to 21.3 . Based on the experimental findings and supporting optical simulations, major performance enhancements by process and layer optimization are identified and a PCE potential of 29.5 for these perovskite silicon tandem solar cells with PERC like bottom cell technology is estimate

Social Assistance in Developing Countries Database Version 5.0

The Social Assistance in Developing Countries Database is a user-friendly tool that provides summary information on social assistance interventions in developing countries. It provides a summary of the evidence available on the effectiveness of social assistance interventions in developing countries. It focuses on programmes seeking to combine the reduction and mitigation of poverty, with strengthening and facilitating household investments capable of preventing poverty and securing development in the longer term. The inclusion of programmes is on the basis of the availability of information on design features, evaluation, size, scope, or significance. Version 5 of the database updates information on existing programmes and incorporates information on pilot social assistance programmes in Latin America, Asia and Africa. It also adopts a new typology that distinguishes between social assistance programmes providing pure income transfers; programmes that provide transfers plus interventions aimed at human, financial, or physical asset accumulation; and integrated poverty reduction programmes. This new typology has, in our view, several advantages. It is a more flexible, and more accurate, template with which to identify key programme features. It provides a good entry point into the conceptual underpinnings of social assistance programmes

ZnO Al a SiOx front contact for polycrystalline silicon on oxide POLO solar cells

Polycrystalline silicon on oxide POLO junctions and related contacting schemes have shown their capability to facilitate high efficiencies for solar cells with passivating selective contacts [1 3]. In this work the front contacting of two side contacted POLO cells with sputtered aluminum doped zinc oxide ZnO Al has been investigated. Different approaches were followed to obtain good lifetimes in cell precursors and keep high Voc values in finished cells. Degradation in minority carrier lifetime and implied Voc iVoc was observed after the ZnO Al sputtering deposition. In order to recover the passivation, various thermal treatments were applied. The necessity to implement a protecting layer to cap the ZnO Al poly Si structures during the annealing treatment to prevent a fill factor degradation in finished cells was observed. Initially an intrinsic a Si H layer was used as a temporary protecting layer. However, during the decapping process, to remove the amorphous layer, lifetime and iVoc are significantly degraded. Therefore a permanent a SiOx protecting layer was implemented for maintaining good passivation Voc 710 amp; 8197;mV . This layer has the additional benefit of improving the optical AR behaviour on finished cells increasing Jsc by 1.5 . The best cell reached a conversion efficiency of 21.