n-n Type Heterojunction Enabling Highly Efficient Carrier Separation in Inorganic Solar Cells

Carrier separation in a solar cell usually relies on the p-n junction. Here we show that n-n type inorganic semiconductor heterojunction is also able to separate the exciton for efficient solar cell applications. The n-n type heterojunction was formed by hydrothermal deposition of Sb2(S,Se)3 and thermal evaporation of Sb2Se3. We found that the n-n junction is able to enhance the carrier separation by the formation of an electric field, reduce the interfacial recombination and generate optimized band alignment. The device based on this n-n junction shows 2.89% net efficiency improvement to 7.75% when compared with the device consisted of semiconductor absorber-metal contact. The study in the n-n type solar cell is expected to bring about more versatile materials utility, new interfacial engineering strategy and fundamental findings in the photovoltaic energy conversion process.