We report a new system for measurement of the spatially resolved quantum efficiency (QE) of the semiconductor solarcells. In our method solar-cell is illuminated by modified liquid crystal display projector scanner. System allows to measure photo-current, and optical properties of the illuminated surface. The same system can be also used to measure surface topography of the wafer, its bow, and warp, and calculate lateral stress in the structure if structure cross-section is known.
I TRODUCTIOFast characterization of solar cell photo-response attracted recently some attention [1]. In one of the approaches [1] the laser beams are moved on the wafer surfaces using a galvanometer xy scanner system and the beam size on the focus has a diameter of about 65 um. This approach allows to obtain quantitative information about the cell quality in time of 3 s using the photo-current maps with a good correlation with the efficiency data.In this paper we present alternative approach where light beam impinging surface of the photocell is defined by means of the modified liquid crystal (LCD) display projector. Recently we developed structured light projection based profilometer for rapid characterization of silicon solar cell wafers described in our earlier paper [2], and subsequent advances in its calibration algorithms [3]. In our earlier paper we demonstrated that structured light projection metrology is capable in meeting throughput requirements for solar cell manufacturing [2]. In this paper we report further advancements in the integration of spectrally, and spatially resolved quantum efficiency measurement. In our approach the quantum efficiency (QE) measurement is accomplished by using the same projector which is used for solar cell topography measurement as a source of illumination. It is possible to use projector to define a light spot on the surface of the sample and to use such spot for investigation of local characteristics of the measured wafer. We demonstrated that the very same hardware as used in profilometer [2], with new modified software application can be used to measure diffused spectrally resolved reflectance. This approach does not only eliminate costly motion stages, but also increases speed of data acquisition. We show that using our system it is possible to vary lateral spot size of the impinging light beam in order to identify and study in detail solar cell anomalies.If the light excitation has known spectrum, and intensity then photo-current can be expressed in terms of quantum efficiency. Therefore we will focus in this paper on photo-current measurement and relative photo-current measurements. The results can be always expressed in terms of QE or relative QE respectively. Measurement technique described here is a variation of LBIC (Light Beam Induced Current) which is a well known and well accepted technique for mapping of the spatial distribution of the photo current of a solar cell [5]- [11]. Just like in the case of LBIC we can use our tool both under short-circuit current conditions or open circ...