Abstract In this chapter, we aim to present an overview of the development of the polymer/inorganic hybrid solar cells. In the first section, we introduce the basic concepts of hybrid solar cells including the device architecture and operation mechanism. Then we summarize the recent progress in this area classified by the nanomorphology of inorganic nanocrystals, including nanoparticles, nanorods, nanowires, and vertically aligned nanoarrays. The nanoscale morphology of the inorganic crystal could play a decisive role in determining the conversion efficiencies of the hybrid solar cells. Finally, we focus on the interface modifications involved in hybrid solar cells. It is noteworthy that an appropriate interface modification could not only facilitate the exciton dissociation but also suppress the backward recombination of carriers and therefore significantly boost the device performance.
To meet the urgent needs for cheap and clean energy, great efforts have been done on the development of the third generation of photovoltaics, including dye-sensitized solar cells (DSSCs)  and bulk heterojunction (BHJ) solar cells [2-4], which have the advantages of low cost, promising power conversion efficiency (PCE), facile fabrication by contact printing  or roll-to-roll process [6, 7] for large area devices, and so on. State-of-the-art BHJ solar cells are composed of conjugated
Q. Tai • F. Yan (H)
Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China e-mail: apafyan@polyu. edu. hk
W. C. H. Choy (ed.), Organic Solar Cells, Green Energy and Technology, DOI: 10.1007/978-1-4471-4823-4_9, © Springer-Verlag London 2013
polymers and fullerene derivatives, which are all organics, therefore, such devices are also called BHJ organic solar cells (OSCs). When the fullerene derivatives are replaced by their inorganic counterparts such as CdSe [8-12], CdS [13–15], TiO2 [16-22], ZnO [23-31], SnO2 , CuInS2  etc., the devices are then named hybrid solar cells (HSCs). Those inorganic materials have the advantages of high dielectric constant, high electron mobility and affinity, and good thermal stability and their optoelectronic properties can be tuned by changing their sizes and shapes, which could facilitate the design of high performance HSCs [34-38].
HSCs have been developed for years and insights of the underlying physics were gradually disclosed. Various inorganic nanocrystals with different morphologies, such as nanoparticle, nanorods, nanowires, and vertically aligned nanorod-, nanowire-, nanotube arrays, have been used together with many conjugated polymers. Both the materials and the nanofabrication techniques are critical issues to the HSCs, which have been developed by many research groups recently. Although the current PCEs of the HSCs are still much lower than the OSCs and DSSCs, higher PCEs are expected in the future when the device physics is further understood and new breakthroughs in synthesis of materials and device fabrication are achieved.
In this chapter, an overview of device structure and operation principle will be first introduced. Then, the developments of HSCs will be reviewed in view of the morphologies of the inorganic nanomaterials. Finally, the interface modification that would help to improve the device performance will be discussed. As there are hundreds of papers have been published in this area, we will not go through all of them but give a glance at the most representative and interesting results.