ZnO can be used as a transparent conducting oxide (TCO) for the front electrode of amorphous silicon solar cells, if it has low electric resistivity and high optical transmittance. We prepared undoped, Al-doped, and $H_2$-doped ZnO films by photo-MOCVD method using diethylzine and $H_2O$ as reactant sources, and characterized those films in order to apply them to amorphous silicon solar cells. The total transmittance at 550nm, haze ratio, and lowest resistivity of the undoped films are 92%, 7.6%, and $8.5×10^{-4} Ωcm$, respectively. The mobility of the Al-doped ZnO film increased and the electron concentration decreased. That is, no conventional doping effect was found. We tried to fabricate $H_2$-doped ZnO films for the first time. The mobility, electron concentration, and deposition rate of the $H_2$-doped films decreased compared to those of the undoped ZnO films. This is because $H_2$ helps oxygen defects to reduce from ZnO thin films. We found that the $H_2$ doped ZnO film was more stable than undoped ZnO films. Thus, we expect that the properties of the interface between the $H_2$-doped ZnO film and the p-layer of amorphous silicon solar cell will improve when it is used as a front electrode of glass/TCO/pin/metal structure. We found the optimized conditions for annealing ZnO films. Those are 160 torr, 150℃ and 1 hour. We prepared amorphous silicon solar cells by using the Al doped and undoped ZnO films which were annealed under the above mentioned conditions, and compared their characteristics. The cell with the Al-doped ZnO film showed improved fill factor, open circuit voltage, and energy conversion efficiency, compared to the cell with the undoped ZnO film.
