Pvi20 Front Cover indd

Bram Hoex
, 
Armin Aberle
, 
Rolf Stangl 
&
 Marius Peters
, Solar Energy Research Institute of Singapore (SERIS), National University of 
Singapore, Singapore
ABSTRACT
In principle solar cells are very simple: they convert sunlight to electricity and can be characterized by a single number 
– the solar cell efficiency. Manufacturers obviously want to achieve this efficiency at the lowest possible cost, so it is 
critical that the efficiency/cost ratio be optimized. To this end, knowledge of where the biggest gains can be achieved is 
key. This paper presents an in-depth loss analysis method developed at the Solar Energy Research Institute of Singapore 
(SERIS) and details how various losses in a silicon wafer solar cell can be quantified, which is not done in the case of 
a conventional solar cell measurement. Through a combination of high-precision measurements, it is shown that 
it is possible to fully quantify the various loss mechanisms which reduce short-circuit current, open-circuit voltage 
and fill factor. This extensive quantitative analysis, which is not limited to silicon wafer solar cells, provides solar cell 
researchers and production line engineers with a ‘health check’ for their solar cells – something that can be used to 
further improve the efficiency of their devices.
Figure 1. Current–voltage curve of a standard industrial p-type Al-BSF silicon wafer solar cell: (a) subjected to a one-sun 
illumination; (b) measurements taken in the dark.
(a)
(b)

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Cell
Processing
using the method of Aberle et al. [2]. The 
experimentally determined full-area 
quantum efficiencies are then active-area 
corrected as shown in Fig. 2 (the correction 
is for reflection from the metallized areas as 
schematically depicted in Fig. 3).
In the following, the corresponding 
measurement results for a standard Al-BSF 
solar cell fabricated at SERIS (schematic 
shown in Fig. 6) are given.
Current losses 
Quantification of the losses in the 
maximum power point current density 
(
J
mpp
) is carried out by applying a bottom-
up loss analysis [1] that quantifies the seven 
most important current loss mechanisms, 
i.e. (1) front metal grid shading; (2) front-
surface reflectance in the active area; (3) 
front-surface escape; (4) shunt resistance; (5) 
non-perfect active-area quantum efficiency; 
(6) forward bias current at the maximum 
power point (‘diode recombination’); and 
(7) photon absorption within the front-side 
dielectric passivation/anti-reflective (AR) 
layer (i.e. silicon nitride SiN
x
).