Evaluation of the conversion efficiency of thin-film single-junction ($a$-Si:H) and tandem ($\mu c$-Si:H + $a$-Si:H) solar cells by analysis of the experimental dark and load current-voltage (I–V) characteristics

The aim of the study is to apply a method commonly used to determine the efficiency of multi-junction nanoheterostructure III–V solar cells by analysis of the dark current-voltage (I–V) characteristics to such an unconventional semiconducting material as amorphous silicon. $a$-Si:H and $a$-Si:H/$\mu c$-Si:H $p$–$i$–$n$ structures without a light-scattering sublayer or an antireflection coating are studied. The results of measurements of the dark I–V characteristics demonstrate that the voltage dependence of the current has several exponential portions. The conversion efficiency of solar cells (SCs) is calculated for each portion of the dark I–V characteristic. This yields a dependence of the potential SC efficiency on the generation current density or on the photon flux. The observed agreement between the data derived from the experimental characteristics and results of calculations can be considered satisfactory and acceptable, thus the method suggested for measurement and analysis of dark I–V characteristics and tested earlier on SCs based on crystalline III–V compounds acquires a universal nature. The analysis of the characteristics of $p$–$i$–$n$ amorphous silicon structures and the calculation of potential efficiencies, based on this analysis, extend the authors’ understanding of this class of devices and make it possible to improve the technology and photoconversion efficiency of SCs of this kind.