Already, several technologies of polycrystalline thin-film photovoltaic materials have achieved certified record small-cell power conversion efficiencies exceeding 22%. They are CdTe, Cu(In,Ga)(S,Se)2 (CIGS), and metal halide perovskite (PSC), each named after the light-absorbing semiconductor material. Thin-film solar cells and modules require very little active material due to their very high absorption coefficient. Efficient production methods with low materials waste, moderate temperatures, attractive cost structures, and favorable energy payback times will play a strong role in market development as thin-film technologies reach full maturity, including mass production and the standardization of production machineries. In fact, the first two technologies have already been developed up to the industrial scale with a market share of several GW. In this review article, we outline similarities and differences between these high-efficiency thin-film technologies from both the materials and the industrial point of view. We address the materials characteristics and device concepts for each technology, including a description of recent developments that have led to very high efficiency achievements. We provide an overview of the CIGS industry players and their current status. The newcomer PSC has demonstrated its potential in the laboratory, and initial efforts in industrial production are underway. A large number of laboratories are experimenting through a wide range of options in order to optimize not only the efficiency but also stability, environmental aspects, and manufacturability of PSC. Its high efficiency and its high bandgap make PSC particularly attractive for tandem applications. An overview of all these topics is included here along with a list of materials configurations.

provide good solubility in organic solvents and processability, we attached branched alkyl substituents at the DTP-nitrogen (ethylhexyl (EH) 1 , 4 , octylnonyl (ON) 2 , 5 , hexyldecyl (HD) 3 , 6 ) and hexyl side chains to each thiophene unit in a regioregular fashion as a mimic of the well-known and frequently used regioregular poly(3-hexylthiophene). [ 26 ] Thereby, the hexyl chains were attached either at the outer ( 1 -3 ) or inner ( 4 -6 ) positions thus yielding three isomeric pairs, which only differ in the positioning of the side chains. As a result, excellent solubilities of ≥120 mg mL −1 in chloroform for molecules 5 and 6 have been obtained. First solar cell results of oligomer pair 1 and 4 have recently been published and we discovered a striking difference between the photovoltaic behavior of the two isomers. [ 16 ] Whereas the so far highest PCE of 4.8% for any DTP-based oligomer has been obtained for oligothiophene 1 and PC 61 BM in BHJSCs, isomer 4 showed a lower performance (0.8%), which we attributed to the different blend morphologies and phase separation probed by atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. [ 16 ] The detailed photovoltaic behavior, further optimization, and characterization of the photoactive layers of the whole series of soluble DTP-oligothiophenes 1 -6 is now described. Signifi cant improvement of the oligomer BHJSC performance was obtained by SVA, which was investigated by absorption spectroscopy, grazing incidence XRD (GI-XRD), and AFM. After extensive optimization, power conversion effi ciencies up to 6.1% and fi ll factors greater than 70% were achieved.

We describe the formation of charge-transfer complexes that feature electron-donating carbon nanodots (CND) and electron-accepting perylenediimides (PDI). The functionalities of PDIs have been selected to complement those of CNDs in terms of electrostatic and π-stacking interactions based on oppositely charged ionic head groups and extended π-systems, respectively. Importantly, the contributions from electrostatic interactions were confirmed in reference experiments, in which stronger interactions were found for PDIs that feature positively rather than negatively charged head groups. The electronic interactions between the components in the ground and excited state were characterized in complementary absorption and fluorescence titration assays that suggest charge-transfer interactions in both states with binding constants on the order of 8×10(4)  M(-1) (25 L g(-1) ). Selective excitation of the two components in ultrafast pump probe experiments gave a 210 ps lived charge-separated state.

Isomeric dicyanovinylene-terminated oligothiophenes 1 and 2 comprising a central dithienopyrrole (DTP) unit have been developed for solution-processed small molecule organic solar cells (SMOSCs) giving the highest power conversion efficiency of 4.8% for DTP-based oligomeric materials.

Solvent vapor annealing (SVA) can strongly influence the morphology of oligomer:fullerene based organic solar cells.