This article presents Solis, a new modular, fast, and portable one-dimensional (1D) semiconductor device simulator designed and developed particularly for photovoltaic solar cells. Solis is coded in standard C++, runs natively on Windows and Linux, and is freely available to download. All the physical models and excitation parameters can be fully controlled using the fast embedded Lua scripting engine. Solis includes a useful set of tools coded in C, such as a code editor, graphical device editor, and data plotter. A material parameters database including well-known semiconductors and their alloys is also included. The Solis calculation engine implements the drift–diffusion transport model and takes into account indirect recombination processes (with user-defined deep or shallow levels) as well as radiative and Auger recombination. The anode and cathode parameters, including the refractive index, extinction coefficient, recombination speed, and barrier height for the Schottky contact, are fully included. It natively handles spontaneous and piezoelectric polarization, which is key for the development of devices based on wurtzite materials. The values of all the material parameters can be graded arbitrarily in position, offering flexibility for the simulation of heterostructure solar cells. In addition, Solis offers functionality needed by researchers to analyze the simulation results, including graphing (of the band diagram, carrier concentration, ionized dopant and trap concentrations, current–voltage and capacitance–voltage characteristics, quantum efficiency, etc.) with complete control of the graph and a useful mathematical console. Solis simulation results for a solar cell using Earth-abundant elements are presented herein. One of the main issues in the development of such solar cells, viz. the inhomogeneity due to phase separation in the absorber, is highlighted.