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Aerosol jet printing is a contactless deposition technique that is ideally suited to depositing features on very thin and fragile substrates such as Si wafers. It can also be used to optimize device geometries including the Al back contact of a Si wafer solar cell quickly. A printable Al ink is required for this process, and we report lines and solar cells prepared with such a material. The resistivities of the printed Al lines approach bulk after appropriate sintering. Al lines printed on Si wafers have been heated over a wide temperature range of 550 to 800 °C to form low resistance contacts suitable for current extraction. Aerosol jet printed Al contacts to industrially produced 21 cm 2 polycrystalline Si solar cells performed on par with all screen printed contacts on similar cells. These promising results demonstrate the potential for non-contact printed Al to contribute to the fabrication of low-cost photovoltaic devices and modules.

Films of gallium-doped zinc oxide (GZO) were deposited on glass substrates by radio-frequency magnetron sputtering using a ceramic target of Ga:ZnO (4 at.% Ga vs. Zn). Both the substrate temperature ( T s ) and the target–substrate distance ( d ts ) were varied and the effect on electrical, optical and structural properties of the resulting films were measured. The highest conductivity of 3200 S/cm was obtained at a deposition temperature of 250 °C, at a d ts of 51 mm. This sample had the highest carrier concentration in this study, 9.6 × 10 20 /cm 3 . Optical transmittance of all films was d ts = 51 mm was smaller than the grain size for films grown with a shorter d ts ; moreover, the films with d ts = 51 mm exhibited the smoothest surface, with a root mean square surface roughness of 2.7 nm. Changes in T s have a more pronounced effect on conductivity compared to changes in d ts ; however, variations in structure do not appear to be well-correlated with conductivity for samples in the 2000–3200 S/cm range. These results suggest that incorporation and activation of Ga is of key importance when attempting to obtain GZO films with conductivities greater than 2000 S/cm.

Thin film pi-conjugated poly(3,4ethylenedioxythiophene): poly(styrenesulphonate) (PEDOT:PSS) as a hole transport layer on indium tin oxide is a key element in some of the most efficient organic photovoltaic and light emitting devices to date. Films are typically deposited by spincoating, which is not readily scalable. In this paper we investigate the critical parameters for both inkjet and ultrasonic spray deposition of PEDOT:PSS thin films on commercial indium tin oxide as a potentially scalable approach to contact formation. Inkjet parameters investigated include drop spacing and substrate temperature. Ultrasonic spray coating parameters investigated include substrate temperature and solution flow rate. We also show that the ink viscosity has a Newtonian character, making it well suited for inkjet printing. Films were characterized via optical profilometry, sheet resistance and atomic force microscopy. Optimized inkjet printed and ultrasonic sprayed PEDOT:PSS films were then compared to spincast layers in a prototypical bulk heterojunction photovoltaic device employing a poly(3-hexylthiophene) and [6,6]-PCBM (6,6-phenylC61-butric acid-methyl ester) blend as the absorber. Practically all three approaches produced devices of comparable efficiency. Efficiencies were 3.6%, 3.5% and 3.3% for spin, spray and inkjet depositions respectively.

Nb doped TiO 2 (Nb:TiO 2 ) is a promising indium-free transparent conducting oxide. We have examined the growth of Nb:TiO 2 thin films by pulsed laser deposition (PLD) on SrTiO 3 , LaAlO 3 , and fused silica. For oriented anatase Nb:TiO 2 films grown on SrTiO 3 by PLD at 550 °C, the conductivity can be as high as 2500 S/cm. A nearly thickness independent conductivity for Nb:TiO 2 demonstrates that the conductivity is a bulk property and not a substrate interface effect. In addition, Nb:TiO 2 films deposited at room temperature were annealed at temperatures up to 750 °C in either vacuum or 1.3 × 10 − 3 Pa O 2 . For these films, conductivities as high as 3300 S/cm on SrTiO 3 and 85 S/cm on LaAlO 3 substrates were obtained for the highest temperature vacuum anneals, albeit with some loss in transparency.

The influence of semiconductor layer morphology on the performance of solution-processed ZnO/Cu2O photovoltaics has been examined. ZnO films were prepared using three highly scalable, cost-effective methods: electrodeposition, zinc acetate decomposition, and diethyl zinc decomposition. To optimize device performance, it is found that a low density of nano-scale pores in the ZnO layer and large grains in the Cu2O is necessary. Through optimizing the ZnO morphology, one of the highest fill factors observed to date (up to 54%) in solution-processed ZnO/Cu2O was achieved. This value is comparable with the fill factor of the record-efficiency ZnO/Cu2O device, which was prepared with much larger energy inputs.