# Status of BIPV and BAPV System for Less Energy-Hungry Building in India--A Review
## 2 PV Technologies for BIPV/BAPV  
Presently PV technologies include first-generation opaque silicon type, second-generation transparent or semitransparent thin film and third or emerging types [12]. Until now, the first generations are employed for BIPV and BAPV applications, whereas second and third generations are primarily considered for BIPV application. Crystalline silicon (c-Si) PV cells are the most widely used and predominant technology in the market due to their mature and long-term durability. Monocrystalline PV cells are made from a single crystal, developed using the Czochralski process with the best-reported efficiency of nearly 22%. Polycrystalline solar cells are developed by melting several fragments of silicon together to form a wafer. Typical efficiency is in the range of 14-18% for polycrystalline PV cells, which is less efficient than the monocrystalline counterparts, since electrons have less freedom of movement due to grain boundaries of many crystals in each cell. However various anti-reflective coatings can be applied onto the surface to change the color of the PV cells. Presently colored silicon PV is also under investigation [13; 14]. The major constraints of crystalline silicon PV cells are power losses due to the shading and at elevated temperature [15; 16; 17; 18; 19; 20; 21; 22]. Thin films include (i) amorphous silicon (a-Si) (ii) Copper - Indium Selenide (CIS) or Copper-Indium-Gallium- Selenide (CIGS), (iii) Cadmium-Telluride (CdTe). The thickness of the film could be a few nanometers to micrometers. These technologies have meager efficiencies in comparison to c-Si, typically 11-12%. However, they have several advantages such as (a) less loss in performance under overcast cloudy climatic conditions and partial shading from obstacles [23; 24] (b) employ lower semiconductor material and hence lower production cost (c) manufacture of transparent or translucent modules using laser scribing [25; 26; 27]. Amorphous silicon is the non-crystalline form of silicon, with atoms disoriented in a random network structure. The major advantage of it is being able to be deposited as thin films on to a moldable substrate like plastic at less than 300 \({}^{\circ}\)C of manufacturing temperature. Moreover, its absorptivity is higher (\(\sim\)40 times) and needs only 1% (about 1 \(\upmu\)m) of material of crystalline silicon, which results in lower making cost/unit-area. Due to its flexible nature, it can be molded into any suitable complex shape for building integration. Although it has high efficiency in comparison to other thin-film technologies, it suffers from degradation due to hydrogenation (Staebler-Wronski effect) [28; 29; 30; 31; 32; 33]. Cadmium telluride (CdTe) is a single-junction solar cell having 1.45 eV bandgap energy. It is a direct bandgap semiconductor nearly ideal for optimal conversion of solar radiation into electricity. An efficiency exceeding 20% has been reported CdTe PV. The major limitations of CdTe cells are its instability and toxicity of cadmium which makes it less suitable for PV application. Copper Indium Gallium Diselenide (CIS) is a polycrystalline compound consisting of copper, indium, gallium, sulphur and selenide elements, with the highest reported conversion efficiency of about 25% in combination with perovskites [34] CIS has high light absorptivity and 0.5 \(\upmu\)m of CIS can absorb 90% of the solar spectrum [35]. Similar to other thin-film technology, CIGSs are semi-transparent and flexible. Emerging third generations are gaining importance due to their low fabrication cost, and transparent and semitransparent makes them a potential candidate for aesthetic building integration. Organic photovoltaics uses organic polymer as the light-absorbing layer. Organic PVs are lightweight, and flexible which allows them to be applied in building as a BIPV system [36; 37; 38]. [PERSON] and [PERSON] carried out seminal work on dye-sensitized solar cells (DSSC) [39]. Since its inception, extensive research was carried out to improve the efficiency and stability of DSSC.