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A large amount of external overpotential is normally required to split water using p-type silicon (p-Si) due to the insufficient driving force between the conduction band-edge and the hydrogen evolution level. We demonstrate how inserting an Al2O3 interlayer between p-Si and the electrolyte mitigates the requirement of overpotentials. Since the Al2O3 film decreased the number of interface defect states, electrons were observed to migrate into the Si surface so that negative charges accumulated at the band-edge of silicon. This resulted in band bending enhancement and a reduction of the overpotential requirement. In our result, the overpotential of ~ 150 mV was reduced at a current density of 20 mA/cm2, and the onset voltage of ~ 70 mV was also reduced at the 1.4 nm thickness of Al2O3 interlayer.

In the solution-based preparation of CZTS (Cu 2 ZnSnS 4 ) thin films followed by a sulfurization process, a layer of MoS 2 is formed at the CZTS–Mo interface. Formation of this MoS 2 layer is mainly governed by the sulfurization process in H 2 S ambient gas rather than diffusion of a sulfur source in the CZTS film. Growth of CZTS grain and grain boundaries facilitates the formation of a MoS 2 layer in any sulfurization process. A decrease in the series resistance and an increase in the current density and solar cell efficiency were achieved through an increase in the temperature of the second sulfurization sequence in a two-step sulfurization sequence. The formation of a CZTS grain dominates the performance of CZTS thin film solar cells with a relatively thin MoS 2 layer, but the performance is degraded by an increase in recombination rate and the hole barrier effect between CZTS and Mo when the MoS 2 is sufficiently thick.

Binary bilayer glass/Mo/In2Se3/Cu2Se precursors have been used to rapidly form CuInSe2. Considering their possible application to large-area deposition processes, bilayer precursors were deposited by sequential radiofrequency sputtering of In2Se3 and direct current sputtering of Cu2Se onto unheated, Mo-coated glass substrates. High-temperature X-ray diffraction analysis of the glass/Mo/Cu2Se sample confirmed that the as-deposited polycrystalline Cu2 − xSe phase is likely transformed to CuSe at approximately 210 °C, and then to CuSe2 at 260 °C. Further increase in temperature resulted in the peritectic decomposition of CuSe2 to CuSe (+ liquid) at approximately 330 °C, and then to Cu2 − xSe (+ liquid) at around 380 °C with the release of Se. Pre-annealing of In2Se3/Cu2Se precursors in Se environment resulted in the formation of a liquid phase, which is in equilibrium with CuSe. Rapid, thermal annealing of pre-annealed samples between 500 and 550 °C apparently enhanced grain growth and reduced the reaction time to about 3 min; this can be explained by a liquid phase-assisted grain growth mechanism.

CuInSe2 (CIS) films on Mo/soda-lime glass were prepared by selenization of sputtered precursors from Cu2Se and In2Se3 binary targets. Cu–In–Se precursors were sequentially sputtered with double-layered structure of both Cu2Se/In2Se3 and In2Se3/Cu2Se. The structural, compositional and electrical properties of annealed Cu–In–Se precursors were investigated for solar cell applications. Better adhesion between CIS and Mo back contact was observed in the double-layered structure of Cu2Se/In2Se3 at all working pressures. Less MoSe2 phase on both structures was generated at a lower working pressure of 0.67 Pa. A CIS solar cell with Al/Al-doped ZnO/i-ZnO/CdS/CIS (900 nm, Cu2Se/In2Se3 at 0.67 Pa)/Mo/soda-lime glass was continuously fabricated, and its conversion efficiency was 4.6%, with 346 mV of open circuit voltage, 30.5 mA/cm2 of short circuit current density and 43.5% fill factor.

Undoped and Al-doped ZnO thin films were prepared by a sol–gel spin coating method. The films were exposed to the electron beam at different energies to improve their electrical properties by modifying their film crystallinity. For both the undoped and Al-doped ZnO thin films, the carrier concentration significantly increased and the resistivity decreased after the introduction of the energetic electron beam. Since band gap widening of the undoped and Al-doped ZnO thin films was also observed with exposure to the electron beam, the behaviors and tendencies can be explained by the Burstein–Moss effect. The effects of the electron beam on ZnO thin film properties, including band gap widening, increasing carrier concentration, and significantly decreased resistivity, were similar to the effects of Al doping in ZnO. Finally, by combining electron beam treatment and Al doping of ZnO thin films prepared by a sol–gel method, the resistivity of the sol–gel synthesized ZnO thin film decreased from 5.8 × 10 2 Ω cm to 8.2 × 10 − 2 Ω cm. According to the Monte Carlo simulation of electron penetration in the ZnO thin film, the penetration depth increased with electron beam energy, which induced lattice heating and atomic rearrangement by electronic excitation in a collision cascade.