An accurate electrical device characterization of hybrid organic-inorganic halide perovskite solar cells (PSCs) is an important prerequisite for further improvement and industrial transfer of this promising photovoltaic technology. In this work, we study the nonlinearity of current versus irradiance as well as the temperature dependence of PSCs in a spectrally resolved manner by highly accurate differential external quantum efficiency (EQE) measurements. We investigate three different types of PSCs fabricated by different research groups. The nonlinearity of all samples is found to be spectrally invariant, which significantly simplifies spectral mismatch corrections. We demonstrate that misinterpretation of EQE measurements can result in a more than 10% relative error in efficiency measurements, if solar simulators are adjusted to photocurrents determined from differential EQEs. For obtaining an accurate integrated photocurrent from EQEs, we introduce a new, convenient approach that accounts for cell nonlinearities but avoids the time-consuming full analysis of spectrally resolved nonlinearity. Moreover, for the samples investigated here, it is shown that the differential EQE measured at 0.35 suns bias irradiance represents a reasonably good estimate of the actual EQE at 1 sun. Furthermore, we determine spectrally resolved temperature coefficients (TCs) and show how the band gap blue shift varies with perovskite absorber and temperature.