## 6 Conclusions  
In this research, a p-type micro-Si thin film was fabricated by MS and CuIC techniques, and its characteristics were measured and analyzed in order to evaluate its suitability for photovoltaic applications. The micro-Si film was created by the deposition of a-Si/a-Cu tandem layers by the DC sputtering method. The prepared samples were annealed at different temperatures, wherein the Cu atoms acted as the inducing metal to reduce the crystallization temperature. The material and crystal properties of the fabricated samples were studied by Raman and XRD spectroscopies. It was confirmed that micro-Si films were formed in the \(<\)111\(>\) plane with a grain size of \(\sim\)20 nm and crystallization ratio of \(\approx\) 93%. The morphology of the micro-Si films was observed to evaluate the quality of the thin film and to understand the mechanism of a-Si crystallization by CuIC. Measurement of the Hall effect showed that Cu can act as a p-dopant, and the hole concentration and mobility of the created micro-Si film may be controlled by the thermal annealing time and temperature. Then, the prepared micro-Si film was used as the emitter layer of a solar cell when it was deposited on a heavily doped n-type Si wafer. The fabricated p-n junction possessed good rectification characteristics under dark conditions, i.e., \(RR=4100\) and \(J_{0}\approx 85\) nA.cm\({}^{-2}\). Under AM1.5 G standard irradiation, the fabricated solar cell showed a noticeable PV effect, with an efficiency of \(\eta=2.7\%\), an open circuit voltage of \(V_{oc}=440\) mV and a short circuit current density of \(J_{sc}=16.7\) mA/cm\({}^{2}\). To our knowledge, this is the most comprehensive demonstration of solar cell fabrication by the CuIC method. Therefore, the proposed method is expected to open up a new path for the fabrication of low-cost, eco-friendly, thin-film Si solar cells. However, the use of such a micro-Si thin film as the emitter layer of a p\({}^{+}\)-n junction solar cell, and the observation of promising PV performance, were only possible after annealing the samples at high temperatures (\(>\)750 \({}^{\circ}\)C); their PV efficiency was not comparable to that of the solar cells made by AIC, for example. Indeed, a big difference between the temperature at which the CuIC started and the temperature where the PV effect became noticeable was observed. The need for high temperature annealing indicates that Cu does not act as a p-dopant well enough at temperatures lower than 750 \({}^{\circ}\)C. This high annealing temperature limits the potential of such a micro-Si layer for the fabrication of thin film solar cells on low-cost substrates. The main drawbacks of these CuIC solar cells are their low \(R_{S}\), \(FF\) and \(J_{sc}\), which were probably due to the high rate of carrier recombination in the p-type micro-Si (the emitter layer of the solar cell). Accordingly, it is necessary to look for a better metal that can be used for the MIC. However, considering that the whole fabrication process can be done in just three steps, we believe that it is interesting and has some potential for further development and optimization. In summary, the highlights of this research are as follows:  
* P-type, micro-Si, thin film preparation by MS and CuIC techniques, as a simple, low-cost, scalable and eco-friendly method for the fabrication of polycrystalline silicon. * Demonstration of p\({}^{+}\)-n junction thin film solar cell fabrication in only three steps, with an emitter layer made by MS and CuIC without any chemical process. * Measuring a photovoltaic conversion efficiency of \(\eta=2.7\%\), an open circuit voltage of \(V_{oc}=440\) mV and a short circuit current density of \(J_{sc}=16.7\) mA/cm\({}^{2}\). * Presenting a simple model for the CuIC principle, and illustrating the mechanism of micro-Si thin film growth during thermal annealing. Conceptualization, D.L. and J.W. ; methodology, D.L., J.W. and O.S. ; validation, O.S., J.W. and D.L. ; formal analysis, O.S. and J.W. ; investigation, O.S. and J.W. ; resources, J.W. and Y.L.