Characterization and optimization of indium tin oxide films for heterojunction solar cells

Well suited and reliable values of the optical and electrical properties of thin indium tin oxide (ITO) films are needed in order to choose the optimal deposition parameters and to perform reliable modeling for solar cells design. In this work, a new method will be presented to evaluate the ITO transparency directly on silicon substrates.The effects of each deposition parameter that influences the ITO transparency and conductivity force a trade-off in the frame of values useful for SHJ solar cells. The deposition of our optimized ITO film on a textured wafer yields a weighted average reflectance as low as 4.4±0.2%.The deposition of an MgF2/ITO double-layer anti-reflection coating (DL-ARC) on textured cells increases the efficiency from 17.9%, measured immediately after contacts have been added to the ITO, to 18.4% after the MgF2 deposition. An annealing step at 200 °C for 10 min proved to further increase the efficiency up to 18.9%, for a total gain of 1%.

Simulated current losses and current generated in the silicon wafer with different oxygen flows. The weight of the various current components is also reported for ITO with an oxygen flow of 0.5 sccm.Figure optionsDownload as PowerPoint slideHighlights
► We examine the effect of the deposition parameters on the properties of ITO.
► We present a new method to evaluate the transmittance of ITO on silicon substrates.
► The effects of a double-layer ARC are taken into consideration.
► The acquired knowledge is used for simulations of complete cells.
► Our optimized MgF2/ITO DL-ARC has a measured efficiency of 18.9%.