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Flexible thin-film solar cells with high weight-specific power density are highly desired in the emerging portable/wearable electronic devices, solar-powered vehicles, etc. The conventional flexible metallic or plastic substrates are encountered either overweight or thermal and mechanical mismatch with deposited films. In this work, we proposed a novel substrate for flexible solar cells based on graphene paper, which possesses the advantages of being lightweight and having a high-temperature tolerance and high mechanical flexibility. Thin-film amorphous silicon (a-Si:H) solar cells were constructed on such graphene paper, whose power density is 4.5 times higher than that on plastic polyimide substrates. In addition, the a-Si:H solar cells present notable flexibility whose power conversion efficiencies show little degradation when the solar cells are bent to a radius as small as 14 mm for more than 100 times. The application of this unique flexible substrate can be extended to CuInGaSe and CdTe solar cells and other thin-film devices requiring high-temperature processing.

Owing to its large work function, MoOX has been widely used for hole-selective contact in both thin film and crystalline silicon solar cells. In this work, thermally evaporated MoOX films are employed on the rear sides of p-type crystalline silicon (p-Si) solar cells, where the optical and electronic properties of the MoOX films as well as the corresponding device performances are investigated as a function of post-annealing treatment. The MoOX film annealed at 100oC shows the highest work function and proves the best hole selectivity based on the results of energy band simulation and contact resistivity measurements. The full rear p-Si/MoOX/Ag contacted solar cells demonstrate the best performance with an efficiency of 19.19%, which is the result of the combined influence of MoOX’s hole selectivity and passivation ability.

Additional file 1: Figure S1. Atomic force microscopy images of the MoOX thin films at different post-annealing temperatures. Figure S2. Green light (532 nm) Raman scattering intensity of polished Si surface and MoOX films. Figure S3. Si 2p XPS spectra of the MoOX films on Si wafers at different post-annealing temperatures. Figure S4. Schematic diagram of the test sample, electrode contact pattern, and test circuit for a specific contact resistivity measurement. Figure S5. Injection-level-dependent effective minority carrier lifetime of bare Si and MoOX films at different post-annealing temperatures

Molybdenum oxide (MoO

Nanostructured metal back reflectors (BRs) are playing an important role in thin-film solar cells, which facilitates an increased optical path length within a relatively thin absorbing layer. In this study, three nanotextured plasmonic metal (copper, gold, and silver) BRs underneath flexible thin-film amorphous silicon solar cells are systematically investigated. The solar cells with BRs demonstrate an excellent light harvesting capability in the long-wavelength region. With the combination of hybrid cavity resonances, horizontal modes, and surface plasmonic resonances, more incident light is coupled into the photoactive layer. Compared to the reference cells, the three devices with plasmonic BRs show lower parasitic absorptions with different individual absorption distributions. Both experimental and simulated results indicate that the silver BR cells delivered the best performance with a promising power conversion efficiency of 7.26%. These rational designs of light harvesting nanostructures provide guidelines for high-performance thin-film solar cells and other optoelectronic devices.