Elmira Ryabova

Novel Back Surface Field (BSF) structure formation by modified solution derived nanocomposite (SDN) method for low cost new cell concept implementation

A novel technology based on a modified hybrid sol-gel technology is presented with PV cell data showing improved performance capability. This “liquid” based approach is envisioned to replace standard Al-BSF with the novel solution based BSF. This latter method can be readily scaled up to the necessary industrial manufacturing levels for c-Si solar cells of virtually any design. Comparative PV test cells were processed and the data show a simultaneous 30% increase in Voc and Jsc accompanied with red shifted spectral IQE graphs using the solution approach. Improved surface passivation is also observed. These results provide the proof-of-concept data. The key advantage is that with this approach, high-quality films with tunable parameters can be generated using low cost, high throughput, non-vacuum processing. Further, various aspects of the materials generated by this approach will enable higher cell performance by providing flexibility in the range of thin film deposition and for extended interface engineering. The approach assists in the progression of the PV roadmap for advanced cell designs envisioned for improved conversion efficiency, as well as for thinner wafers, both of which will impose significant demands and constraints on processing conditions.

PV dispatchability and intermittency: Potential limitations to PV growth, and critical strategies

The level of PV installations is rapidly approaching >35GW worldwide. Conventional wisdom is that the need for renewables will continue the drive to increased PV implementation. However, there are several key points of concern which are now developing which may limit the expansion of PV and need to be addressed. The following issues may begin to limit the sustained PV growth: (1) as PV and renewables reach a significant level of energy generation, at what point will the Utilities not be accepting the inputs for various reasons, (2) if the grid is not accepting the PV power input then what is the impact on the FIT models of revenue generation, (3) at what level is the “dispatchability” requirement a major factor in determination of the PV choice, (4) what are the best strategies for storage and what are the current developments particularly for CSP (Concentrated Solar Power), as well as more standard approaches more suitable to PV. This paper examines key developing trends across the globe where the issues of PV supply may be impacted by larger considerations such as the grid availability. The ultimate goal of baseline energy from PV requires addressing intermittency, dispatchability and storage. A survey of storage is provided with a focus on CSP options. The relative cost considerations of the different solar approaches are examined. The aspect of grid “readiness” for acceptance is also examined with case studies. Market research analysis is developed looking at the specifics of dispatchability, regional grid issues, and storage. Quantitative comparisons for different solar approaches and wind are presented. Learning from the wind sector is highlighted as it is ∼10× that of PV. Specific strategies are developed and discussed in the context of preparation for acceleration of solar as a power source.

Materials considerations for PV markets: Guideposts for technology directions

The primary metrics for PV systems are cost and efficiency. We propose to put more emphasis on additional metrics representing materials properties related to their availability and toxicity. While toxicity and availability have been discussed in recent years within the PV community and identified as recurrent concerns, they are not yet an integral part of the decision-making process about new PV projects. This paper outlines specific materials of concern and provides an analysis which is intended to enumerate important questions. We show that not only the actual material availability, but also geographic and political aspects of the supply chain, as well as chemical and environmental properties, and further processing requirements must all be addressed to minimize market restrictions during the product lifecycle. The value of this market analysis is to provide a broader perspective of the market conditions to help guide scientific development paths.

PV technology roadmap: Market and manufacturing considerations

Technology roadmaps are an important tool for all technology arenas and there is increasing activity to develop an ITRS equivalent for PV. This paper makes the following key points: (1) the PV industry has 2 essential differences from the semiconductor industry which must be reflected in the roadmap (2) there are several types of PV roadmaps which provide different perspectives, and (3) this paper suggests that for PV, production volume instead of time is the preferred variable and may lead to better technology forecasts. The example of PV wafer thickness is used to illustrate these points.

Methodology for defect impact studies under conditions of low sampling statistics

A methodology is described which determines the kill rate of defects based on electrical testing using a short loop yield monitoring under conditions of low statistics. The results provide a quantitative means to rank the importance of defects as well as the effectiveness of the inspection strategy. Electrical test results form specifically designed test patterns for interconnect structures and correlated with optical defect inspection data to quantify the kill rates of various defects. A unique and important features of the approach is the use of deliberately introduced defects to study the impact at specific process points. The use of controlled defect inspection at each process step allows an improved statical analysis for low coverage inspection plans. The wafers are optically process step allows an improved statistical analysis for low coverage inspection plans. The wafers are optically inspected at all process steps and reviewed with an automated SEM. The defects are tracked and a defect Pareto is established. The defect management system provides direct correlations between electrical fails and optical defects. It appears that particles that occur at early stages in the process have an enhanced impact because of a potential size amplification effect. With the impact quantified, optimized inspection and defect reduction plans can be implemented.

Methodology of a short-loop yield analysis for defect impact studies

A methodology is described which establishes the prioritization of defects based on electrical impact of the different defect types using a Short Loop Yield Monitor under conditions of low statistics. Probe results from specifically designed test patterns for interconnect structures are correlated with optical defect inspection data to determine the kill rates of various defects. The results provide quantitative means to rank the importance of defects as well as the effectiveness of the inspection strategy. The wafers are optically inspected at each process step and reviewed with an automated SEM (SEMVision). The defects are tracked and a defect Pareto is established. After final processing, the electrical testing is performed and correlations are established. The defects are ranked by a quantitative approach based on the kill rate. A unique and important feature of the approach is to use deliberately introduced defects to study the impact at specific process points. The use of controlled defect introduction allows an improved statistical analysis for low coverage inspection plans. It appears that particles that occur at early stages in the process have an enhanced impact because of a potential size amplification effect. With the impact quantified, effective inspection and defect reduction plans can be implemented.