Improving CNT-Si solar cells by metal chloride-to-oxide transformation

Transitional metal oxides(TMOs)are important functional materials in silicon-based and thin-film optoelectronics.Here,TMOs areapplied in carbon nanotube(CNT)-Si solar cells by spin-coating solutions of metal chlorides that undergo favorable transformation in ambient conditions.An unconventional change in solar cell behavior is observed after coating two particular chlorides(MoCl,and WCls,respectively),characterized by an initial severe degradation followed by gradual recovery and then well surpassing the original performance.Detailed analysis reveals that the formation of correspondina oxides(MoOa and WO.)enables two primary functions on both CNTs(p-type doping)and Si(inducing inversion layer),leading to significant improvement in open-circuit voltage and fill factor,with power conversion efficiencies up to 13.0%(MoOg)and 13.4%(WOg).Further combining with other chlorides to increase the short-circuit current,ultimate cells efficiencies achieve>16%with over 90%retention after 24 h,which are among the highes stable efficiencies reported for CNT-Si solar cells.The transformation of functional layers as demonstrated here has profoundinfluence on the device characteristics,and represents a potential strategy in low-cost manufacturing of next-generation high efficiency photovoltaics.