Only a small part of the incident solar energy converts to the electrical power in photovoltaic devices. The majority of the energy loss contributes to the heat generation in devices and thus leads to a temperature rise, causing an inevitable impact on the performance of photovoltaic devices. Hence, loss processes in solar cells play very important roles in solar-electric conversion process. This paper systematically studies both the intrinsic and extrin. Only a small part of the incident solar energy converts to the electrical power in photovoltaic devices. The majority of the energy loss contributes to the heat generation in devices and thus leads to a temperature rise, causing an inevitable impact on the performance of photovoltaic devices. Hence, loss processes in solar cells play very important roles in solar-electric conversion process. This paper systematically studies both the intrinsic and extrinsic losses in solar cells. Energy distributions of solar cells with different kinds of parameters are presented to characterize the different kinds of loss processes in detail. The sensitivities of loss processes to the structural and operating parameters of solar cells such as external radiative efficiency, solid angle of absorption and operating temperature are discussed, for the parameters have significant impact on the loss processes. The external radiative efficiency, solid angle of absorption (e.g., the concentrator photovoltaic system), series resistance and operating temperature are demonstrated to greatly affect the loss processes. Furthermore, based on the calculated thermal equilibrium states, the temperature coefficients of solar cells versus the bandgap Eg are plotted.••••Dominant losses and parameters of affecting the solar cell efficiency are discussed.••Non-radiative recombination loss is remarkable in high-concentration-ratio solar cells.••Series resistance plays a key role in limiting non-radiative recombination loss.Solar cellLoss processSensitivityEfficiencySolar energy photovoltaic technology has developed rapidly for the past years and researchers over the world have been working hard on improving the efficiency and reducing the cost of photovoltaic devices. However, the efficiency of photovoltaic devices grows slowly in recent years. Many groups have been studying the limiting efficiency and the factors that limit the efficiency of photovoltaic devices, trying to find effective ways to reduce the energy loss in the process of photovoltaic energy conversion and increase the final output efficiency [,,,,,,,, ].Shockley and Queisser developed the detailed balance approach with generalized Planck function to derive the maximum power point and give the elementary detailed balance limit of efficiency, which only involved the fundamental loss processes. Henry published a graphical method, which clearly demonstrated the distribution of various intrinsic losses for both single and multiple energy gap ideal solar cells and gave the maximum work done by per absorbed photon. Wurfel published the thermodynamic limitations to solar energy conversion based on the second principle of thermodynamics, which is the highest efficiency of photovoltaic devices theoretically. Hirst and Ekins-Daukes studied the mechanisms of five intrinsic loss processes quantitatively and provided a mathematical and graphical demonstration. 2.1. Intrinsic losses in solar cellsLoss processes in solar cells consist of two parts: intrinsic losses (fundamental losses) and extrinsic losses. Intrinsic losses are unavoidable in single bandgap solar cells, even if in the idealized solar cells. In this paper, intrinsic losses are divided into six processes: the optical loss, the below Eg loss, the thermalization loss, the emission loss, the Carnot loss and the angle mismatch loss, and the model in this paper is based on the model presented by Dupré et al. [11,12,14].The optical loss corresponds to the fraction of incident energy of the Sun's radiation that is reflected or transmits through the cells.(1)POptical=n∫0∞(Rc+Tc)PFD(E)·EdEwhere n is the concentration ratio of the cells (n suns), Rc and Tc are the reflectance and transmittance of the cells, respectively. PFD(E) is the AM1.5 photon flux density as a function of photon energy E.The below Eg loss corresponds to the fraction of the photons transmit into the cells that have the energy below the bandgap Eg. These photons don't have enough energy to excite free electrons across the bandgap and finally their energy is transferred to phonons in the device, contributing to heat generation instead of electricity.(2)PBelow=n∫0Eg(1−Rc−Tc)PFD(E)·EdEThe thermalization loss originates from the fraction of the photons transmit into the cells that have the.
