Green technology innovations propel both economic development and environmental sustainability. Exploring the contributing factors to green technology innovations carries important policy implications, but research from the perspective of supply chain relationships has been rare. This paper examines the impact of corporate customer concentration on green technology innovations and explores its influencing mechanisms using the data of Chinese A-share listed companies. The results show that a high customer concentration inhibits the quantity and quality of green technology innovations, a finding that is robust when endogeneity is addressed and when alternative measures and an alternative estimation model are employed. Financing constraints and social responsibility play intermediary roles in the impact of customer concentration on green technology innovations. A high customer concentration tends to increase corporate financing constraints and reduce corporate social responsibility performance, which hinder green technology innovations. The heterogeneity analysis reveals that the inhibitory effect of customer concentration on green technology innovations is less severe in digitally transformed enterprises, mature enterprises, or enterprises with a high level of market power. As this study provides a novel perspective on the contributing factors to corporate green innovations, it offers important policy recommendations.