Solar Photovoltaic Technologies

Transcription

1 Sola Photovoltaic Technologies Pof. C.S. Solanki Enegy Systems Engineeing IIT Bombay

2 Contents Bief summay of the pevious lectue esistive losses Emitte loss Effect of esistive losses on Fill Facto Summey of losses in semiconducto 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-2

3 esistive osses: Seies esistance, s Contibuting factos to s : Finges 1. the movement of cuent though the emitte and base of the sola cell Bus ba M-S contact emitte Base p-laye N-laye 2. the contact esistance between the metal contact and the silicon 3. esistance of the top and ea metal contacts 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-3

4 esistive losses , 5, and 6 ould be minimized 1, 2 and 4 ae usually negligible, if coect metal is chosen fo ohmic contact 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-4

5 Contact esistance Heavy doping unde contact to minimize contact N esistance Metal to semiconducto contact Contact esistance losses occu at the inteface between the silicon sola cell and the metal contact. To keep top contact losses low, the top N+ laye must be as heavily doped as possible. c exp( Cont. N bn A high doping ceates a "dead laye. D Ohmic contact, High doping, tunneling contact 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-5

6 Sheet esistance In diffused semiconducto layes, esistivity is a stong function of depth. It is convenient to a paamete called the "eet esistance" (s. W t t A W 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-6 s W s is called eet esistance with unit of ohms/squae o Ω/ (actual unit is Ohms The /W atio can be thought of as the numbe of unit squaes (of any size Sheet esistance of a sola cell emitte is in the ange of 30 to 100 Ω/

7 Emitte esistance: Powe loss N t d d/2 P Zeo cuent flow exactly at midpoint of finges 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-7 x Maximum cuent density at I the finge edge max J 2 esistance d in infinitesimally thin laye of d d t

8 Emitte esistance: Powe loss d t d t eet incemental powe loss dp I 2 ( J x 2 ( eet Integation of the powe fom 0 to d/2 will give the total powe loss P J 3 2 d eet 24 Finge spacing is a citical paamete of design it ould be caefully chosen such that adowing losses ae also not high 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-8

9 Top contact design Design citeia: minimize losses (esistive, adow h w d w h Emitte finge and busba spacing, the metal height-to-width, aspect atio, the minimum metal line width and the esistivity of the metal One example of top metal contact design 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies 27-9

10 Effect of s and FF I sc I Medium s age s Slope of the I-V cuve nea V oc gives indication about s P P0(1 V m, s s Chaacteistic esistance, ch V oc FF CH 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies s FF s (1 V I CH s 0 s max max Nomalized seies esistance, s Effect of seies esistance on the FF and maximum powe

11 Effect of on FF I sc I Medium Slope of the I-V cuve nea I sc gives indication about V Nomalized unt esistance, V oc 8/1/2008 IIT Bombay, C.S. Solanki Sola Photovoltaic Technologies m, CH Effect of seies esistance on the FF and maximum powe P FF P (1 0 FF0 (1 1 1