This paper aims to investigate the role of sustainability factors in the diffusion of solar photovoltaic (PV) technologies. A combined economic innovation-diffusion model that accounts for additional sustainability aspects is proposed. Two and three-stage least square methods were used for the empirical estimation, and the results were compared to a maximum entropy econometric estimation. The findings indicate that sustainability characteristics (i.e., cell efficiency) have a statistically significant positive effect on installed capacity in all solar PV technologies under analysis. Results show that multijunction PV modules have a learning rate of 17.1%, while Monojunction and the global aggregate have similar learning rates of 19.5% and 19%, respectively. Thin film PV modules have learning rates of 17.9% for the period 1991–2019. Cost reductions in solar PV modules can be largely attributed to learning-by-doing activities, the effects of learning by searching are ambiguous and depend both on the estimation methodology and the period under analysis. The study recognizes the difficulty in measuring sustainability characteristics, such as social aspects of the SDGs or indirect environmental implications but suggest that qualitative research can complement the quantitative analysis.