1 Key Laboratory of Novel Thin Film Solar Cells, Institute of Applied Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230088, China 2 University of Science and Technology of China, Hefei 230026, China 3 Beijing Key Laboratory of Novel Thin Film Solar Cells, North China Electric Power University, Beijing 102206, China
Owing to their special three-dimensional network structure and high specific
surface area, TiO2 submicrospheres have been widely used as electron conductors
in photoanodes for solar cells. In recent years, utilization of TiO2 submicrospheres
in solar cells has greatly boosted the photovoltaic performance. Inevitably,
however, numerous surface states in the TiO2 network affect electron transport.
In this work, the surface states in TiO2 submicrospheres were thoroughly
investigated by charge extraction methods, and the results were confirmed by
the cyclic voltammetry method. The results showed that ammonia can effectively
reduce the number of surface states in TiO2 submicrospheres. Furthermore,
in-depth characterizations indicate that ammonia shifts the conduction band
toward a more positive potential and improves the interfacial charge transfer.
Moreover, charge recombination is effectively prevented. Overall, the cell
performance is essentially dependent on the effect of the surface states, which
affects the electron transfer and recombination process.