Characteristics and value enhancement of cast silicon ingots

Casting technologies of multi-crystalline (mc) silicon ingots in photovoltaic industry are reviewed in this paper and three main types of cast ingots are introduced. Cell efficiency distribution of the three types of ingots, i.e. common mc-silicon ingots, mono-like silicon ingots and super high efficiency mc (S-mc) silicon ingots, is examined, calculated and compared. It is found that the cell efficiency distribution of the three types of ingots is different because of their different defect characteristics. Common mc-silicon is used as the study baseline. Both mono-like and S-mc wafers have significantly better cell performance. Solar cells made from mono-like wafers have high efficiency close to mono-crystalline CZ wafers, however, the efficiency distribution is wide. Meanwhile, S-mc silicon wafers have much narrower cell efficiency distribution than mc-silicon wafers and mono-like silicon wafers in the experiments. Main defects affecting cell performance are studied and the theories of how grain size affects cell performance are discussed in the paper too. Moreover, several casting technologies which can be used to achieve even higher quality cast ingots to further increase solar cell efficiency are proposed. These new casting technologies only increase the manufacturing cost on a small scale, however, they will greatly boost the wafers value in the solar market and accelerate the progress of Grid Parity. •Three main types of casting ingots for photovoltaic industry are introduced.•Cell efficiency distribution of the three ingots is calculated and compared.•Cell performance of the three ingots varies with their defect characteristics.•Main defects in the three types of wafers affecting cell performance are studied.•The theories of how grain size affects mc-silicon cell performance are discussed.