# Overview on Different Types of Solar Cells: An Update
## 2 Organic Solar Cells
### Efficiency Highlights  
Generally, organic compounds are considered to be non-conductors. The discovery of conducting polymers was a breakthrough in this context. Recently, conjugated polymers have gained significant attention is OSC technology since they can act as electron donors in the active layer of OSC. Tandem solar cells prepared by a bulk heterojunction possessing complementary absorbing materials have achieved better performance compared with single cells. Easy processing, low entropy of mixing, and efficient exciton dissociation are the major advantages associated with polymer solar cells compared with small-molecule  
Figure 4: Current voltage (IV) curve of organic solar cells. solar cells. In this section, we briefly discuss the important highlights of the maximum efficiency achieved by OSC. P3 HT is a classical donor conjugated polymer which show comparatively low PCE. A significant improvement in the PCE and other performance parameters for a P3 HT-based OSC was recently reported as the introduction of additives [99]. P3 HT was used as the donor with 2,2'-(2Z,2'Z)-((12,13-bis(2-butyloctyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]-thiadiaizolo [3,4-e]thieno [2',3\":4',5']thieno [2',3':4,5]pyrro [3,2-g]thieno [2',3':4,5]thieno [3,2-b]indole-2,10-diyl)bis(methane-lyidene))bis(5,6-dichloro-1H-indene-1,3(2H)-dione) (ZY-4 CI) as the acceptor while using SA4 as a solid additive. The additive caused enhanced molecular packing and phase separation, which ultimately resulted in an augmented charge transport and the reduced recombination of carriers. The V\({}_{\rm OC}\), I\({}_{\rm SC}\), FF, and PCE of the manufactured dev ice were found to be 0.90 V, 17.0 mA/cm\({}^{2}\), 0.67, and 10.24%, respectively. The OSC composed of bithienyl-benzodithiophene-_all_-fluorobenzzotriazole copolymers/ITIC indicated remarkably high I\({}_{\rm SC}\), \(V_{\rm OC}\), FF, and PCE of 17.43 mA/cm, 0.89 V, 0.64, and 9.53%, respectively [100]. The same group demonstrated an improvement in the OSC performance by changing the acceptor material [101]. Herein, the authors introduced meta-alkyl-phenyl substitution on ITIC. While using bithienyl-benzodithiophene-_all_-fluorobenzzotriazole copolymers as the donor and substituted ITIC (m-ITIC) as the acceptor, a significant improvement in the performance parameters was achieved. A higher PCE of 11.7% along with a V\({}_{\rm OC}\) of 0.912 V, FF of 0.70, and I\({}_{\rm SC}\) of 18.31 mA/cm\({}^{2}\) was shown by the reported OSC device. In this context, a new conjugated polymer donor and small molecule acceptor were synthesized, namely, Poly[(2,6-(4,8-bis(5-(2-ethylhexylthio)-4-fluorothiophen-2-yl)-benzo [1,2-b:4,5-b']dithiophene)-alt-(5,5-(1',3'-di-2-thienylyl-5,7'-bis(2-ethylhexyl)benzo [1',2'-c-4',5']-c']dithiiophene-4,8-dione)) (PBDB-T-SF) and 3,9-bis(2-methylene-((3-(1,1-dicyanomethylhene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno [2,3-d:2',3'-d']-s-indaceno [1,2-b:5,6-b']dithiophene (ITIC-4F) by [PERSON] and co-workers [102]. The OSC based on PBDBT-SF:IT-4F possessed significantly higher I\({}_{\rm SC}\) (20.50 mA/cm\({}^{2}\)), V\({}_{\rm OC}\) (0.88 V), FF (0.719), and PCE (13%). Moreover, a single-junction OSC made of poly[(2,6-(4,8-bis(5-(2-ethylhexyl))thiophen-2-yl)benzo [1,2-b:4,5b']dithiiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)]benzo [1,2-c:4,5-c']dithiiophene-4,8-dione)] (PBDB-T) as the donor and 3,9-bis(2-methylene-((3-(1,1-dicyanomethylhene)-6/7-methyl)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno [2,3-d:2',3'-d']-s-indaceno [1,2-b:5,6-b']dithiiophene (ITIC-M) as the acceptor achieved a PCE of 12.05% [103]. The values of V\({}_{\rm OC}\), I\({}_{\rm SC}\), and FF of the fabricated OSC were found to be 0.94 V, 17.44 mA/cm\({}^{2}\), and 0.735, respectively. Possibilities of improvements in the multijunction efficiency based on the design principles were demonstrated by combining tandem with a solution-processed non-fullerene-acceptor-based infrared-absorbing subcell on a visible-absorbing fullerene-based subcell [104].