The rhetoric of inquiry

In this chapter, the authors use the rapidly rising perovskite solar cells as a case to illustrate the rich facets of material interface engineering. Perovskite semiconductors are quite different from the organic semiconductors for photovoltaic applications whose recombination dynamics are usually dominated by excitons. The free-carrier model is more suitable than the exciton model for interpreting the properties of perovskite, wherein charge transport and separation take place more like in a heterojunction solar cell. Trap state at the perovskite surface and interfaces can lead to the charge accumulation and recombination losses in the device, and it had been observed that the passivation of trap states can eliminate the hysteresis phenomenon. In traditional metal electrode-based perovskite solar cells, solar light passing through the perovskite layer can be reflected by a smooth metal electrode, enabling a secondary absorption. Consequently, the thickness of perovskite layer is usually in the relatively low range.