High-efficiency Both-sides-contacted Silicon Solar Cells. Requirements and Options

The photovoltaic industry is dominated by crystalline silicon solar cells. While interdigitated back contact cells have yielded the highest efficiency, both sides-contacted cells are the preferred choice in industrial production due to their lower processing complexity. Typically, such industrial cells feature a pn junction at the front surface. In order to identify an ultimate design for both-sides-contacted cells, we have studied here different cell designs at a very high performance level. We demonstrate a very conversion efficiency of 26.0% for a both-sides-contacted silicon solar cell, which exhibits the pn junction at the back surface in form of a full area passivating contact based on poly crystalline silicon. One key feature of this advanced cell structure is the highly transparent front surface based on dielectric passivation layers without any lateral conductivity. A detailed power loss analysis reveals that this cell balances electron and hole transport losses as well as transport and recombination losses in general. On the base of this analysis we performed a systematic simulation study for a variety of different solar cell designs, which led to some fundamental design rules for future >26% efficiency silicon solar cells. We discuss further requirements and design options for these solar cells to improve the device performance even further.