This section introduces some variations to the basic process described above that aim at improving the efficiency, the throughput or the cost. While some modifications are already in production, others are still being developed at the laboratory.
Wafering and sheet-growth techniques improve and produce thinner substrates, with wafer thickness around 150|im or below being envisaged for the near term [140, 141]. When processing these thin cells several relevant issues appear.
The probability of fracture during handling increases, especially in conjunction with a larger size. Adequate handling tools must be designed. Some steps appear to be critical: for instance, in chemical baths convection can exert significant torque on the wafers. This issue is fostering the study of the mechanical properties of silicon [142-144] and even the development of new crystallization procedures.
The behavior during heat treatments is modified due to a decreased thermal mass. On the other hand, wafers can more easily become bowed [145]. Processes need to be specifically optimized for thin cells [146-148].
Thin cells largely depend on surface passivation and optical confinement. If attained to reasonable degrees, efficiency improvement comes as a bonus for thin cells, but otherwise the performance is degraded. New optimal structures must be developed.
