Tax or subsidy? On the way that government supports green smartphone production and consumption

As the world's largest smartphone market, China faces the twin imperatives of tackling e-waste pollution and enabling a green technology transition to achieve its ''dual-carbon'' goals. We expand the analysis from a two-party (enterprise-consumer) model to a tripartite (government-enterprise-consumer) model. Numerical simulations and parameter sensitivity analyses are conducted using actual data from Guangdong Province and leading manufacturers including Xiaomi, Huawei, and TCL to validate the theoretical hypotheses. The results show that market mechanisms alone cannot drive the green transition of smartphone production and consumption, so government intervention is necessary. Furthermore, taxation and subsidies are the government's two principal policy instruments, which can raise the cost of conventional smartphones, improve the relative profitability of green smartphones, and stimulate green market demand. In addition, tax-based instruments outperform subsidies in overall effectiveness, and consumer subsidies stimulate demand faster than enterprise subsidies. Finally, combined tax and subsidy strategies generally outperform single-policy instruments. These findings offer theoretical and practical insights for policymakers and industry stakeholders seeking to accelerate the green transition of the smartphone industry.