Reactively sputtered tungsten oxide (WOx) was investigated as hole contact on n-type crystalline silicon. Varying the oxygen gas flow during sputtering enables variation of the WOx conductivity from 0.01 to 1000 Ω/cm, while the band bending at the interface and the implied fill factor (FF) change by 70 meV and 1.5 %. Sputtered WOx shows higher resistivity and higher absorption in the visible range compared to ITO. Therefore stacks of WOx and ITO are used in solar cells. It was found that at least 20 nm thick WOx is needed to prevent detrimental effects of the ITO work function on the band bending at the junction, the implied FF and real FF of solar cells. WOx hole contacts of different thicknesses and conductivity were applied in solar cells and it was found that the highest FF is achieved using about 20 nm thick interlayers of WOx with the highest possible conductivity. It was found that sputtering enables a drastic improvement of WOx/silicon solar cells compared to thermal evaporation, due to the precise control of the WOx conductivity. Unfortunately the resistivity of sputtered WOx is still limiting the FF of these devices.

Open-Circuit Voltage Decay (OCVD) method was investigated for few decades as a simple and convenient method to characterize effective lifetime into Ge and Si p-n homojunctions. Minority carrier lifetime (MCL) is an important parameter to optimize device design where being able to investigate one type of carriers is an important goal. The p-n homojunction design is of major importance to reach that purpose by OCVD. We carried out Technology Computer Aided-Design simulations of the OCVD signal. The study focused on Si and GaAs p-n homojunctions. We looked into bulk thickness and doping level influences on bulk lifetime extraction. Previously, those influences have not been quantified for Si and never investigated for GaAs. MCL accurate extraction from bulk required a bulk thickness at least 4 times higher than diffusion length and emitter doping levels at least 2 orders of magnitude higher than bulk. Likewise, the paper shows different accuracy of extraction between GaAs/Si and p-type/n-type bulk in p-n homojunction.

Open-Circuit Voltage Decay is a method to characterize minority carrier effective lifetime (τ ef f). It is non-destructive, simple and low-cost. It has been mainly used in silicon p-n junctions. τ ef f is a very important parameter to optimize device design but also to supervise process steps. Actually, it is not the only parameter we can obtain by OCVD. Due to the intrinsic space charge region (SCR) capacitance of a p-n junction, doping level of the lowest-doped region (N l) and built-in potential (V bi) are extractable. Moreover, it is also possible to obtain the shunt resistance (R sh) value when it has a significant effect on the p-n junction behaviour. We first applied the well-established one-diode model in transient regime to simulate OCVD signal. In a second step, we used an optimization algorithm to fit the experimental curve of a silicon diode in order to extract τ ef f , N l , V bi and R sh. These values were compared to those obtained from C-V and I-V. Results are promising and demonstrates for the first time, the flexibility of the OCVD method. It opens up the perspective for development of add-on features of the method and for measuring short lifetime.