Optical Characteristics and Operational Principles of Hybrid Perovskite Solar Cells

In this article, the optical properties of various APbX(3)-type hybrid perovskites (A: center cation; X: halogen atom) and operational principles of hybrid perovskite solar cells are reviewed and discussed. In particular, controversy observed for the absorption coefficient () of CH3NH3PbI3 is found to originate from large surface roughness of the solution-processed perovskite layers. The comparison of the accurate experimental with the theoretical results indicates clearly that the hybrid perovskite has a direct band gap with negligible indirect nature. Moreover, the A-site cation plays a critical role in determining the absorption strength of hybrid perovskites through hydrogen bonding interaction. In contrast to general understanding that hybrid perovskite solar cells operate in p-i-n type solar cells, a simple p-n junction formation explains the observed solar cell characteristics well. The high short-circuit current observed in the solar cells is further interpreted by the suppressed parasitic light absorption and efficient optical confinement in the solar cells, rather than the high of hybrid perovskite materials. This article provides renewed principles for the optical processes and operation of hybrid perovskite solar cells.