Optimization of ALD $$\hbox {Al}_{2}\hbox {O}_{3}$$ process parameters for passivation of c-silicon and its implementation on industrial monocrystalline silicon solar cell

Abstract

Effect of process parameters on \(\hbox {Al}_{2}\hbox {O}_{3}\) deposited using Atomic Layer Deposition (ALD) for the surface passivation of c-silicon surface has been investigated. Surface passivation properties of \(\hbox {Al}_{2}\hbox {O}_{3}\) have been measured by evaluating the minority carrier lifetime and interface charges at the \(\hbox {Si}/\hbox {Al}_{2}\hbox {O}_{3}\) interface. It has been observed that surface passivation properties of \(\hbox {Al}_{2}\hbox {O}_{3}\) are strongly dependent on process parameters such as substrate temperature, annealing temperature, and thickness of the deposited \(\hbox {Al}_{2}\hbox {O}_{3}\) film. Minority carrier lifetime, effective charge density (\(Q_{{\mathrm{eff}}}\)), and interface defect density (\(D _{{\mathrm{it}}}\)) were observed to vary from 180 to \(355\,\upmu \hbox {s}\), \(-\,2.3 \times 10^{12}\) to \(-1.46 \times 10^{13}\,\hbox {cm}^{-2}\) and \(1.2 \times 10^{9}\) to \(1.9\times 10^{10}\,\hbox {eV}^{-1}\,\hbox {cm}^{-2}\), respectively, for various process parameters. \(\hbox {Al}_{2}\hbox {O}_{3}\) film based on the optimized process parameters were then used as a passivation layer in fabricating industrial PERC solar cells. Effect of \(\hbox {Al}_{2}\hbox {O}_{3}\) passivation in PERC solar cells has been demonstrated by comparing the characteristics of the PERC solar cells with that of the standard Al BSF solar cells. An efficiency improvement of \(\sim 0.8\%\) has been observed in passivated emitter rear cells (PERC) solar cells as compared to the standard aluminum back surface field (Al BSF) solar cells.