Photovoltaic devices based on nanocomposites composed of conjugated polymers and inorganic nanocrystals show promise for the fabrication of low-cost third-generation thin film photovoltaics. In theory, hybrid solar cells can combine the advantages of the two classes of materials to potentially provide high power conversion efficiencies of up to 10%; however, certain limitations on the current within a hybrid solar cell must be overcome. Current limitations arise from incompatibilities among the various intradevice interfaces and the uncontrolled aggregation of nanocrystals during the step in which the nanocrystals are mixed into the polymer matrix. Both effects can lead to charge transfer and transport inefficiencies. This paper highlights potential strategies for resolving these obstacles and presents an outlook on the future directions of this field. 1. Introduction Hybrid solar cells combine both organic and inorganic semiconductors in an active layer such that the organic or polymer semiconductor serves as the electron donor and transports photogenerated holes, whereas the inorganic semiconductor accepts and transports electrons [1–6]. Theoretically, the hybrid photovoltaic devices (HPVs) are expected to achieve a high power conversion efficiency (PCE) because they combine the advantageous characteristics of polymers and nanocrystals (NCs), including the flexibility, light weight, and low fabrication costs of polymer materials [7–9] and the high electron mobility, size-dependent optical properties [10, 11], and physical and chemical stability of inorganic NCs [12]. Unfortunately, the PCE values obtained thus far in hybrid devices have not exceeded 4% under simulated air mass (AM) 1.5 illumination [13]. The main barriers to a higher PCE are thought to be an inefficient exciton dissociation at the donor/acceptor (D/A) interface [14–16], inhibition of recombination [17, 18], and poor charge transport to the electrodes [19–21]. Therefore, the design of compatible surfaces, accounting for the different chemical properties of the organic and inorganic materials, and control over the phase separation of the composites are crucial for achieving rapid and high-yield charge separation at the D/A interface and for promoting charge transport and collection at the electrodes. Three distinct strategies have been explored toward improving the interface design in the nanocomposite materials to enable hybrid solar cells to achieve high PCE. The first approach, ligand exchange, uses a mix of polymers and inorganic NCs prepared via colloidal synthesis approaches. The
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