Hybrid solar cells (HSCs) based on conjugated polymers and inorganic nanocrystals (NCs) have attracted increased attention, owing to the combination of the solution processability of polymers and the adjustable absorption properties of NCs. In previous reports, the material preparation and device fabrication are based on organic solvents, which typically include chloroform, chlorobenzene, toluene. The organic solvents need careful handling and personal protective equipment and will inevitably give rise to environmental pollution.
Recently, using water-soluble materials for solar cells has seen increased attention, although the power conversion efficiency (PCE) is still less satisfactory than it is expected to be. Prof. Bai Yang and coworkers firstly demonstrated the fabrication of efficient polymer/NC hybrid solar cells completely from aqueous PPV precursor and CdTe nanocrystals. PEDOT:PSS and ZnO were selected as the hole transport layer and electron transport layer, respectively. A PCE of 2.14% was achieved, which was the highest value of solar cells from aqueous materials (Energy Environ. Sci., 2011, 4, 2831–2834). As the existence of PEDOT:PSS will decrease the stability of solar device and spin-coating the water-soluble active layer will lead to partly dissolution of PEDOT:PSS, solar devices with inverted structures were fabricated. Compared to the normal device, the PCE was increased to 3.61%, which was comparable to the HSCs based on organic solvent (Adv. Energy Mater. 2012, DOI: 10.1002/aenm.201200741). To increase the photocurrent, the n–i structure was constructed by introducing a CdTe buffer layer between the TiO2 and blend layer. Eventually, a record power conversion efficiency of 4.76% was achieved and the maximum Jsc can reach 16.08 mA/cm2 (Energy Environ. Sci., 2013, DOI: 10.1039/c3ee40481a).